Even Albert Einstein Had His Doubts About Black Holes

Even Albert Einstein Had His Doubts About Black Holes

More than a century ago, Albert Einstein stunned the world when he explained the universe through his theory of general relativity. The theory not only described the relationship between space, time, gravity and matter, it opened the door to the theoretical possibility of a particularly mind-boggling phenomenon that would eventually be called black holes.

The concept that explains black holes was so radical, in fact, that Einstein, himself, had strong misgivings. He concluded in a 1939 paper in the Annals of Mathematics that the idea was “not convincing” and the phenomena did not exist “in the real world.”

The unveiling of the first-ever picture of a black hole by the Event Horizon Telescope in April 2019, however, not only confirmed Einstein’s original theory, but also provided indisputable proof that the gravitational monsters are, in fact, real.

The Space-Time Theory

As described by American physicist John A. Wheeler, general relativity governs the nature of space-time, particularly how it reacts in the presence of matter: “matter tells space-time how to curve, and space-time tells matter how to move.”

Picture a flat rubber sheet (space-time) suspended above the ground. Place a bowling ball in the middle of the sheet (matter) and the sheet will distort around the mass, bending half way to the floor— this is matter telling space-time how to curve. Now roll a marble (matter) around the rubber sheet (space-time) and the marble’s trajectory will change, being deflected by the warped sheet— this is space-time telling matter how to move. Matter and space-time are inextricably linked, with gravity mediating their interaction.

Now, place a singularity—a theoretical point of infinite density—onto the sheet, what would happen to space-time? It was German theoretical physicist Karl Schwarzschild, not Einstein, who used general relativity to describe this hypothetical situation, a situation that would become the most extreme test of general relativity.

At a certain threshold, Schwarzschild found that the hypothetical singularity would literally punch through space-time. In mathematics, singularities are interesting numerical solutions, but astrophysical singularities were, at the time, thought to be an abomination— there was no known mechanism that could produce them.

Schwarzschild, however, persisted until his death in 1916, realizing that an astrophysical singularity would warp space-time so severely that even light would not be fast enough to get out of the space-time hole that the singularity would create. The point of no return, a spherical region surrounding the singularity, would become known as the “event horizon.”

Known physics breaks down beyond the event horizon and, as no information can escape, we can have no experience as to what lies inside. Though this was an interesting concept, there was no known mechanism that could create a singularity in nature, so the idea was largely overlooked.

Concept of Black Holes Are Born

That was until 1935, when Indian astrophysicist Subrahmanyan Chandrasekhar realized that, should a massive star run out of fuel, the sheer gravitational pressure of that mass would be concentrated to a point, causing space-time to collapse in on itself. Chandrasekhar had bridged the gap between mathematical curiosity and a scientific possibility, seeding the theory behind the formation of a real singularity with extreme consequences for the fabric of space-time.

Even with Chandrasekhar’s contributions toward the modern understanding of the nature of black holes, astrophysical singularities were assumed to be, at best, extremely rare. It stayed that way until the 1960s when British theoretical physicists Stephen Hawking and Roger Penrose proved that, far from being rare, singularities were a part of the cosmic ecosystem, and are a part of the natural evolution of massive stars after they run out of fuel and die.

And it wasn’t until 1967, 12 years after Einstein’s death in 1955, that these astrophysical singularities became known as “black holes”—a term coined by American physicist John A. Wheeler during a conference in New York to describe the grim fate of a massive star after it runs out of fuel and collapses in on itself.

The black hole “teaches us that space can be crumpled like a piece of paper into an infinitesimal dot, that time can be extinguished like a blown-out flame, and that the laws of physics that we regard as ‘sacred,’ as immutable, are anything but,” Wheeler wrote in his 1999 autobiography.

Thanks to astronomers and computer scientists working with the Event Horizon Telescope (EHT), a network of eight linked telescopes, humanity was finally able to visualize these "infinitesimal dots." Although Einstein wasn’t alive to see evidence of black holes—the result of real singularities about which he remained doubtful—his theory of relativity made their discovery possible.

And, no doubt he also would have marveled at the ghostly crescent surrounding a near-perfect dark disk: proof that even the most outrageous theories can turn out to be true.

Ian O'Neill is an astrophysicist and science writer.


When Black Holes Collide: Einstein Was Right All Along

One hundred years ago, Albert Einstein published his general theory of relativity, which described how gravity warps and distorts space-time.

While this theory triggered a revolution in our understanding of the universe, it made one prediction that even Einstein doubted could be confirmed: the existence of gravitational waves.

Today, a century later, we have that confirmation, with the detection of gravitational waves by the Advanced Laser Interferometer Gravitational-Wave Observatory (aLIGO) detectors.

Here we collect reactions and analysis from some of the leading astronomers and astrophysicists from around the world.

Keith Riles, University of Michigan

Keith Riles explains gravitational waves.

Einstein was skeptical that gravitational waves would ever be detected because the predicted waves were so weak. Einstein was right to wonder&mdashthe signal detected on September 14, 2015 by the aLIGO interferometers caused each arm of each L-shaped detector to change by only 2 billionths of a billionth of a meter, about 400 times smaller than the radius of a proton.

It may seem inconceivable to measure such tiny changes, especially with a giant apparatus like aLIGO. But the secret lies in the lasers (the real "L" in LIGO) that are projected down each arm.

Fittingly, Einstein himself indirectly helped make those lasers happen, first by explaining the photoelectric effect in terms of photons (for which he earned the Nobel Prize), and second, by creating (along with Bose) the theoretical foundation of lasers, which create coherent beams of photons, all with the same frequency and direction.

In the aLIGO arms there are nearly a trillion trillion photons per second impinging on the mirrors, all sensing the precise positions of the interferometer mirrors. It is this collective, coherent sensing that makes it possible to determine that one mirror has moved in one direction, while a mirror in the other arm has moved in a different direction. This distinctive, differential motion is what characterizes a gravitational wave, a momentary differential warp of space itself.

By normally operating aLIGO in a mode of nearly perfect cancellation of the light returning from the two arms (destructive interference), scientists can therefore detect the passage of a gravitational wave by looking for a momentary brightening of the output beam.

The particular pattern of brightening observed on September 14 agrees remarkably well with what Einstein's General Theory of Relativity predicts for two massive black holes in the final moments of a death spiral. Fittingly, Einstein's theory of photons has helped to verify Einstein's theory of gravity, a century after its creation.

Amanda Weltman, University of Cape Town

The results are in and they are breathtaking. Almost exactly 100 years ago Einstein published "Die Feldgleichungen der Gravitation" in which he laid out a new theory of gravity, his General Theory of Relativity. Einstein not only improved on his predecessor, Newton, by explaining the unexpected orbit of the planet Mercury, but he went beyond and laid out a set of predictions that have shaken the very foundations of our understanding of the universe and our place in it. These predictions include the bending of light leading to lensed objects in the sky, the existence of black holes from which no light can escape as well as the entire framework for our modern understanding of cosmology.

Einstein's predictions have so far all proven true, and today, the final prediction has been directly detected, that of gravitational waves, the tiniest ripples through space the energy radiated away by two massive heavenly bodies spiralling into each other. This is the discovery of the century, and it is perhaps poetic that one of the places it is being announced is Pisa, the very place where, according to legend, 500 years ago, Galileo dropped two massive objects to test how matter reacts to gravity.

As we bathe in the glory of this moment it is appropriate to ask, what is next for astronomy and physics and who will bring about the next revolution? Today's discovery will become tomorrow's history. Advanced LIGO brings a new way of testing gravity, of explaining the universe, but it also brings about the end of an era of sorts. It is time for the next frontier, with the Square Kilometre Array project finally afoot across Africa and Australia, the global South and indeed Africa itself is poised to provide the next pulse of gravity research.

Stephen Smartt, Queen's University Belfast

Not only is this remarkable discovery of gravitational waves an extraordinary breakthrough in physics, it is a very surprising glimpse of a massive black hole binary system, meaning two black holes that are merging together.

Black holes are dark objects with a mass beyond what is possible for neutron stars, which are a type of very compact stars&mdashabout 10 km across and weighing up to two solar masses. To imagine this kind of density, think of the entire human population squeezed onto a tea spoon. Black holes are even more extreme than that. We've known about binary neutron stars for years and the first detection of gravitational waves were expected to be two neutron stars colliding.

What we know about black hole pairs so far comes from the study of the stars orbiting around them. These binary systems typically have black holes with masses five to 20 times that of the sun. But LIGO has seen two black holes with about 30 times the mass of the sun in a binary system that has finally merged. This is remarkable for several reasons. It is the first detection of two merging black holes, it is at a much greater distance than LIGO expected to find sources, and the total mass in the system is also much larger than expected.

This raises interesting questions about the stars that could have produced this system. We know massive stars die in supernovae, and most of these supernovae (probably at least 60%) produce neutron stars. The more massive stars have very large cores that collapse and are too massive to be stable neutron stars so they collapse all the way to black holes.

But a binary system with two black holes of around 30 solar masses is puzzling. We know of massive binary star systems in our own and nearby galaxies, and they have initial masses well in excess of 100 suns. But we see them losing mass through enormous radiation pressure and they are predicted, and often observed, to end their lives with masses much smaller&mdashtypically about 10 times the sun.

If the LIGO object is a pair of 30 solar mass black holes, then the stars that formed it must have been at least as massive. Astronomers will be asking'&mdashhow can massive stars end their lives so big and how can they create black holes so massive? As well as the gravitational wave discovery, this remarkable result will affect the rest of astronomy for some time.

Alan Duffy, Swinburne University

The detection of gravitational waves is the confirmation of Albert Einstein's final prediction and ends a century-long search for something that even he believed would remain forever untested.

This discovery marks not the end, but rather the beginning, of an era in which we explore the universe around us with a fundamentally new sense. Touch, smell, sight and sound all use ripples in an electromagnetic field, which we call light, but now we can make use of ripples in the background field of space-time itself to "see" our surroundings. That is why this discovery is so exciting.

The Advanced Laser Interferometer Gravitational-Wave Observatory (aLIGO) measured the tiny stretching of space-time by distant colliding black holes, giving them a unique view into the most extreme objects in general relativity.

The exact "ringing" of space-time as the ripples pass through the detector test this theory and our understanding of gravity in ways no other experiment can.

We can even probe the way galaxies grow and collide by trying to measure the gravitational waves from the even larger collisions of supermassive black holes as the galaxies they are contained in smash together.

Australia in particular is a leading nation in this search, using distant pulsars as the ruler at the Parkes telescope.

Tara Murphy, University of Sydney

In addition to binary black holes, aLIGO will detect gravitational waves from other events such as the collision of neutron stars, which are the dense remnants left over when a massive stars collapse.

Astronomers think that two neutron stars colliding may trigger a gamma-ray burst, which we can detect with "regular" telescopes.

Simulation of neutron stars colliding. Credit: NASA

In Australia, we have been using the Murchison Widefield Array and the Australian Square Kilometre Array Pathfinder) to follow-up aLIGO candidates.

aLIGO is an incredibly sensitive instrument but it has very poor ability to determine where the gravitational waves are coming from. Our radio telescopes can scan large areas of sky extremely quickly, so can play a critical part in identifying the event.

This project has been like no other one I have worked on. When aLIGO identifies a candidate, it sends out a private alert to an international network of astronomers. We respond as quickly as possible with our telescopes, scanning the region the event is thought to have occurred in, to see if we can detect any electromagnetic radiation.

Everything is kept top secret&mdasheven the other people using our telescopes are not allowed to know where we are pointing them.

To make sure their complex processing pipeline was working correctly, someone in the aLIGO team inserted fake events into the process. Nobody on the team, or those of us doing follow-up, had any idea whether what we were responding to was real or one of these fake events.

We are truly in an era of big science. This incredible result has been the work of not only hundreds of aLIGO researchers and engineers, but hundreds more astronomers collaborating around the globe. We are eagerly awaiting the next aLIGO observing run, to see what else we can find.

Tamara Davis, University of Queensland

Rarely has a discovery been so eagerly anticipated.

When I was a university undergraduate, almost 20 years ago, I remember a physics lecturer telling us about the experiments trying to detect gravitational waves. It felt like the discovery was imminent, and it was one of the most exciting discoveries that could be made in physics.

Mass and energy warping the fabric of space is one of the pieces of general relativity that most captures the imagination. However, while it has enormous explanatory power, the reality of that curvature is hard to grasp or confirm.

For the last few months I've had to sit quietly and watch as colleagues followed up the potential gravitational wave signal. This is the one and only time in my scientific career that I wasn't allowed to talk about a scientific discovery in progress.

But that's because it is such a big discovery that we had to be absolutely sure about it before announcing it, lest we risk "crying wolf."

Every last check had to be done, and of course, we didn't know whether it was a real signal, or a signal injected by the experimenters to keep us on our toes, test the analysis and follow-up.

I work with a project called the Dark Energy Survey, and with our massive, wide-field, half-billion pixel camera on a four metre telescope in Chile, my colleagues took images trying to find the source of the gravitational waves.

The wide-field is important, because the gravitational wave detectors aren't very good at pinpointing the exact location of the source.

Unfortunately if it was a black hole merger, we wouldn't expect to see any visible light.

Now that we're in the era of detecting gravitational waves, though, we'll be able to try again with the next one.

Maria Womack, University of South Florida

This is a momentous change for astronomy. Gravitational-wave astronomy can now truly begin, opening a new window to the universe. Normal telescopes collect light at different wavelengths, such as Xray, ultraviolet, visible, infrared and radio, collectively referred to as electromagnetic radiation (EM). Gravitational waves are emitted from accelerating mass analogous to the way electromagnetic waves are emitted from accelerating charge both are emitted from accelerating matter.

The most massive objects with the highest accelerations will be the first events detected. For example, Advanced LIGO, funded by the U.S. National Science Foundation, can detect binary black holes in tight, fast orbits. GWs carry away energy from the orbiting pair, which in turn causes the black holes to shrink their orbit and accelerate even more, until they merge in a violent event, which is now detectable on Earth as a whistling "chirp."

An example signal from an inspired gravitational wave source. A. Stuver/LIGO, CC BY-ND

The gravitational-wave sky is completely uncharted, and new maps will be drawn that will change how we think of the universe. GWs might be detected coming from cosmic strings, hypothetical defects in the curvature of space-time. They will also be used to study what makes some massive stars explode into supernovae, and how fast the universe is expanding. Moreover, GW and traditional telescopic observing techniques can be combined to explore important questions, such as whether the graviton, the presumed particle that transmits gravity, actually have mass? If massless, they will arrive at the same time as photons from a strong event. If gravitons have even a small mass, they will arrive second.

Daniel Kennefick, University of Arkansas

Almost 100 years ago, in February 1916, Einstein first mentioned gravitational waves in writing. Ironically it was to say that he thought they did not exist! Within a few months he changed his mind and by 1918 had published the basis of our modern theory of gravitational waves, adequate to describe them as they pass by the Earth. However his calculation does not apply to strongly gravitating systems like a binary black hole.

It was not until 1936 that Einstein returned to the problem, eventually publishing one of the earliest exact solutions describing gravitational waves. But his original sceptical attitude was carried forward by some of his former assistants into the postwar rebirth of General Relativity. In the 1950s, doubts were expressed as to whether gravitational waves could carry energy and whether binary star systems could even generate them.

One way to settle these disputes was to carry out painstaking calculations showing how the emission of gravitational waves affected the motion of the binary system. This proved a daunting challenge. Not only were the calculations long and tedious, but theorists found they needed a much more sophisticated understanding of the structure of space-time itself. Major breakthroughs included the detailed picture of the asymptotic structure of space-time, and the introduction of the concept of matched asymptotic expansions. Prior to breakthroughs such as these, many calculations got contradictory results. Some theorists even got answers that the binary system should gain, not lose, energy as a result of emitting gravitational waves!

While the work of the 1960s convinced theorists that binary star systems did emit gravitational waves, debate persisted as to whether Einstein's 1918 formula, known as the quadrupole formula, correctly predicted the amount of energy they would radiate. This controversy lasted into the early 1980s and coincided with the discovery of the binary pulsar which was a real-life system whose orbit was decaying in line with the predictions of Einstein's formula.

In the 1990s, with the beginnings of LIGO, theorists' focus shifted to providing even more detailed corrections to formulas such as these. Researchers use descriptions of the expected signal as templates which facilitate the extraction of the signal from LIGO's noisy data. Since no gravitational wave signals had ever been seen before, theorists found themselves unusually relevant to the detection project &ndash only they could provide such data analysis templates.

David Parkinson, University of Queensland

Gravitational waves can be used to provide a direct probe of the very early universe. The further away we look, the further back in time we can see. But there is a limit to how far back we can see, as the universe was initially an opaque plasma, and remained so even as late as 300,000 years after the Big Bang.

This surface, from which the cosmic microwave background is emitted, represents the furthest back any measurement of electromagnetic radiation can directly investigate.

But this plasma is no impediment for gravitational waves, which will not be absorbed by any intervening matter, but come to us directly. Gravitational waves are predicted to be generated by a number of different mechanisms in the early universe.

For example, the theory of cosmic inflation, which suggests a period of accelerated expansion moments after the Big Bang, goes on to predict not just the creation of all structure that we see in the universe, but also a spectrum of primordial gravitational waves.

It is these primordial gravitational waves that the BICEP2 experiment believed it had detected in March 2014.

BICEP2 measured the polarisation pattern of the cosmic microwave background, and reported a strong detection of the imprint of primordial gravitational waves. These results turned out in fact to be contamination by galactic dust, and not primordial gravitational waves.

But there is every reason to believe that future experiments may be able detect these primordial gravitational waves, either directly or indirectly, and so provide a new and complementary way to understand the physics of the Big Bang.

This article was originally published on The Conversation. Read the original article.


Did Einstein Prematurely Reject Gödel’s Universe?

Artist’s impression of time travel. Mathematically, some forms of time travel are logically self-consistent. (Image: Andrey_l/Shutterstock)

Interestingly, Einstein did publicly endorse and promote Gödel’s essay on time. He hailed it as, ‘an important contribution to the general theory of relativity’ and ‘especially to the concept of time’.

Not All Time Travel Is Illogical

Gödel hoped that the logical inconsistency he had found in the theory of general relativity would force us to revisit, and perhaps radically revise, our concept of time.

Einstein and Gödel did agree about the questions raised by Gödel’s essay. In particular, they both recognized and agreed that the existence of closed timelike curves would make it impossible for one to distinguish the past from the future. They also agreed that the lack of a well-defined direction of causality in such a system could lead to paradoxes, and oftentimes to illogical nonsense.

This, however, doesn’t mean that all kinds of time travel are problematic. In some cases, they’re not. Some kinds of time travel are entirely logically self-consistent.

Let’s take the example involving a pair of twins. One twin travels through space at nearly the speed of light and returns to Earth. To the moving twin, only a few years of time passed during the trip. But on Earth—and to the stationary twin—a full century of time and history had played out.

By moving at nearly the speed of light, the moving twin traveled not only through space, but also through time, and into the future. There are no logical problems with this. In principle, if you can move fast enough, you can move arbitrarily far into the future. A thousand years. A million years. A billion years. Or more.

The Grandfather Paradox

The serious logical problems start to appear with backward time travel. The most famous illustration of these kinds of problems is known as the ‘grandfather paradox’.

Explanation of the Grandfather Paradox using a billiard ball. The original ball enters the time machine, it then emerges from the future and strikes the original ball, preventing it from entering the time machine. So, the paradox is if the original ball never entered the time machine, how did it emerge from the future to divert its path? (Image: BrightRoundCircle/CC BY-SA 4.0)

Imagine that you follow a closed timelike curve to a point in the past. At this point, you encounter and kill your own grandfather while he’s still a child. As a consequence of these actions, your grandfather never grows up. He never meets your grandmother, and he never has any children or grandchildren. This means you’re never born. Therefore, you never exist, and that means that you never travel backward through time to kill your grandfather.

So, since he was never killed, your grandfather survives to meet your grandmother, and they do have children and grandchildren together. So once again, you do exist. And then you do travel through time to kill your grandfather.

Backward time travel makes it impossible for there to be a self-consistent timeline.

This is a transcript from the video series What Einstein Got Wrong. Watch it now, Wondrium.

The grandfather paradox has been a staple of science fiction since the 1930s. In addition to producing some very entertaining storytelling, it also serves to illustrate the logical hazards that can come with unrestricted time travel.

Any system in which it is possible to change the past suffers from these kinds of problems, which means that any system containing closed timelike curves seems sure to lead to paradoxical nonsense.

You should also keep in mind that this conclusion doesn’t only apply to people or other living things that might travel through time. An electron, for example, might travel through a closed timelike curve only to prevent it from ever coming into existence. On fairly general grounds, the existence of closed timelike curves seems to break the very logical self-consistency of a universe.

For these and other reasons, Einstein doubted that Gödel’s result could have any real physical meaning or other physical implications. He didn’t doubt that Gödel’s math was correct because it was perfect. However, Einstein didn’t think that all mathematically valid solutions to the equations of general relativity were necessarily physically valid solutions.

Einstein Prematurely Dismissed Many Valid Solutions

There are a number of cases where Einstein applied his intuition in order to decide whether or not a given solution to his field equations was physically meaningful.

Take black holes, for example. Black holes are described by a valid solution to the field equations, first identified in 1915. Einstein had refused to believe that objects like these could ever form. Only well after Einstein died, did astronomers begin to discover real black holes in our universe?

Albert Einstein delivering a lecture at Vienna in 1921. Einstein had dismissed several solutions to his field equations, only to be proven wrong later. (Image: F Schmutzer/Public Domain)

We now know that very massive stars inevitably become black holes, and supermassive black holes occupy the centers of most galaxies. However, throughout his entire life, Einstein refused to believe that such objects were, in fact, physically possible.

Another example would be the expansion of the universe. Until Edwin Hubble proved him wrong, Einstein rejected the possibility that the universe might be expanding or contracting. Instead, his intuition led him to insist that the universe must be static.

When we take examples such as these into account, we see that Einstein had a far from the perfect record when it came to deciding which solutions to his field equations were physically real and which were not.

This leads us back to the question at hand. Was Einstein correct to reject the physical significance of Gödel’s universe? And what, if anything, does Gödel’s work tell us about general relativity? Or about the nature of time itself?

At the time, it was probably impossible to know whether Einstein was right to disregard any physical significance of Gödel’s cosmological solution. Throughout his life, Einstein often played the role of the skeptic, and this was no exception. Gödel’s essay on time had identified what seemed to be a very surprising aspect of general relativity, but when faced with these surprising consequences, Einstein’s instincts told him that this result probably didn’t really matter.

Einstein did have some good reasons to support this choice. Gödel’s solution to the field equations doesn’t describe the universe that we actually live in. Gödel’s universe isn’t expanding, while ours definitely is. Also, there’s no evidence that our universe is rotating the way that Gödel’s is. So, the universe that we live in is clearly very different from the one described by Gödel’s solution.

So, someone with Einstein’s outlook could simultaneously acknowledge that Gödel’s universe seems to have some logical inconsistencies, but at the same time, he could argue that our universe—the real universe—doesn’t necessarily suffer from any of these problems. Maybe our universe doesn’t contain any closed timelike curves.

If there are no closed timelike curves in our universe, then maybe there aren’t any underlying problems with time either—at least not with the way that time seems to exist in our world.

However, in my opinion, this is where Einstein went wrong. Or at least where he seems to have reached these conclusions prematurely.

When Gödel pointed out that closed timelike curves could exist, even in a hypothetical universe, this gave us a deep and good reason to worry about the self-consistency of general relativity itself. Even though we don’t actually live in a universe like the one described by Gödel’s solution, it’s not clear that our universe is entirely safe from the kinds of logical inconsistencies that could be associated with the existence of closed timelike curves.

Common Questions about Kurt Gödel’s Universe

Time travel is not possible , as of now. However, mathematically, if one can move at the speed of light or faster, one can move arbitrarily far into the future. In the case of backward time travel, serious logical problems start to appear, even in a mathematical system.

The grandfather paradox is the most famous example of the types of problems that present themselves with backward time travel. This form of a time paradox has been written in science fiction stories as early as the 1930s. So, we don’t know who was the first to create the grandfather paradox, but one of the earliest examples can be found in a letter to the American science fiction magazine Amazing Stories.

A closed timelike curve is essentially a path through space and time that makes it possible for someone to be present for some event, and then to travel through space only to later encounter the same event again. Here the same event isn’t a recurrence of the original event. It is the original event. The observer has simply followed a path through their universe that has taken them from the future into the past.

In a mathematical sense, certain forms of time travel are entirely logically self-consistent. However, in the case of backward time travel, a number of time paradoxes appear. One of the most famous illustrations of such a time paradox is the grandfather paradox. The result of such a time paradox is that there’s no possibility of a self-consistent timeline.


In the special relativity paper, in 1905, Einstein noted that, given a specific definition of the word "force" (a definition which he later agreed was not advantageous), and if we choose to maintain (by convention) the equation mass x acceleration = force, then one arrives at m / ( 1 − v 2 / c 2 ) /c^<2>)> as the expression for the transverse mass of a fast moving particle. This differs from the accepted expression today, because, as noted in the footnotes to Einstein's paper added in the 1913 reprint, "it is more to the point to define force in such a way that the laws of energy and momentum assume the simplest form", as was done, for example, by Max Planck in 1906, who gave the now familiar expression m / 1 − v 2 / c 2 /c^<2>>>> for the transverse mass.

As Miller points out, this is equivalent to the transverse mass predictions of both Einstein and Lorentz. Einstein had commented already in the 1905 paper that "With a different definition of force and acceleration, we should naturally obtain other expressions for the masses. This shows that in comparing different theories. we must proceed very cautiously." [1]

Einstein published (in 1922) a qualitative theory of superconductivity based on the vague idea of electrons shared in orbits. This paper predated modern quantum mechanics, and today is regarded as being incorrect. The current theory of low temperature superconductivity was only worked out in 1957, thirty years after the establishing of modern quantum mechanics. However, even today, superconductivity is not well understood, and alternative theories continue to be put forward, especially to account for high-temperature superconductors. [ citation needed ]

Einstein denied several times that black holes could form. [ citation needed ] In 1939 he published a paper that argues that a star collapsing would spin faster and faster, spinning at the speed of light with infinite energy well before the point where it is about to collapse into a Schwarzchild singularity, or black hole.

The essential result of this investigation is a clear understanding as to why the "Schwarzschild singularities" do not exist in physical reality. Although the theory given here treats only clusters whose particles move along circular paths it does not seem to be subject to reasonable doubt that more general cases will have analogous results. The "Schwarzschild singularity" does not appear for the reason that matter cannot be concentrated arbitrarily. And this is due to the fact that otherwise the constituting particles would reach the velocity of light. [2]

This paper received no citations, and the conclusions are well understood to be wrong. [ citation needed ] Einstein's argument itself only shows that stable spinning objects have to spin faster and faster to stay stable before the point where they collapse. But it is well understood today (and was understood well by some even then) that collapse cannot happen through stationary states the way Einstein imagined. Nevertheless, the extent to which the models of black holes in classical general relativity correspond to physical reality remains unclear, and in particular the implications of the central singularity implicit in these models are still not understood.

Closely related to his rejection of black holes, Einstein believed that the exclusion of singularities might restrict the class of solutions of the field equations so as to force solutions compatible with quantum mechanics, but no such theory has ever been found. [ citation needed ]

In the early days of quantum mechanics, Einstein tried to show that the uncertainty principle was not valid. By 1927 he had become convinced of its utility, but he always opposed it. [ citation needed ]

In the EPR paper, Einstein argued that quantum mechanics cannot be a complete realistic and local representation of phenomena, given specific definitions of "realism", "locality", and "completeness". The modern consensus is that Einstein's concept of realism is too restrictive. [ citation needed ]

Einstein himself considered the introduction of the cosmological term in his 1917 paper founding cosmology as a "blunder". [3] The theory of general relativity predicted an expanding or contracting universe, but Einstein wanted a universe which is an unchanging three-dimensional sphere, like the surface of a three-dimensional ball in four dimensions.

He wanted this for philosophical reasons, so as to incorporate Mach's principle in a reasonable way. He stabilized his solution by introducing a cosmological constant, and when the universe was shown to be expanding, he retracted the constant as a blunder. This is not really much of a blunder – the cosmological constant is necessary within general relativity as it is currently understood, and it is widely believed to have a nonzero value today.

Einstein did not immediately appreciate the value of Minkowski's four-dimensional formulation of special relativity, although within a few years he had adopted it within his theory of gravitation. [ citation needed ]

Finding it too formal, Einstein believed that Heisenberg's matrix mechanics was incorrect. He changed his mind when Schrödinger and others demonstrated that the formulation in terms of the Schrödinger equation, based on wave–particle duality was equivalent to Heisenberg's matrices. [ citation needed ]

Einstein spent many years pursuing a unified field theory, and published many papers on the subject, without success.


The Man Who Said No to Einstein

It takes a brave man to reject a scientific paper by Albert Einstein. But that’s what the physicist Howard Percy Robertson did in 1936, as editor of the journal Physical Review. Einstein was so enraged that he never published there again.

If Einstein were alive today, he might thank Robertson, who saved the great scientist from retracting the most far-reaching prediction of his theory of relativity – the existence of gravitational waves. The first direct detection of Einstein’s waves was announced this week to much fanfare and celebration. Scientists say the waves emanated from the powerful collision of two black holes.

The finding was hailed as a vindication, though Einstein was one of the biggest doubters of his own idea. He flip-flopped several times over the years, said physicist Daniel Kennefick, co-author of An Einstein Encyclopedia. The tale ended well, thanks to Einstein’s wisdom in knowing when to be sure, when to have doubts, when to ignore his doubters and when to listen to them and regroup.

The idea grew out of Einstein’s relativity theories. He published his special theory of relativity in 1905, changing the way scientists understood space and time. He published the general theory in 1915 and changed the way scientists understood gravity, redefining it as the effect of curves in space and time.

In February of 1916, Einstein predicted that if space and time could have lumps and bumps, then perhaps those bumps could move, said Kennefick. �ter all, we can see moving hills and valleys on the surface of water that we call waves, so if gravity curves space-time, why couldn&apost it create moving distortions?”

Einstein understood that these waves would be subtle. Only something dramatic could emit a signal strong enough to provide a chance to detect them – something like a merger of black holes. But Einstein was skeptical about the existence of black holes at all, even though others predicted them based on his theory.

These doubts didn&apost mean that that Einstein was insecure. He boldly predicted that the curve of space would produce a visible bending of starlight around the sun.

That prompted the world’s best astronomers to see for themselves, waiting for a 1919 eclipse of the sun to make the behavior of faint light from background stars measurable. When asked how he&aposd feel if relativity was disproved by the eclipse experiment, Einstein famously replied: “Then I would feel sorry for the dear Lord. The theory is correct anyway.”

Einstein knew when to be certain, said Kennefick. He had a good physical intuition, and he also knew when he was ranging around in new territory.

So it’s perhaps understandable that he would at one point decide to quash his gravitational-wave prediction in a high profile journal article. In hindsight, one could see Robertson’s rejection as a double negative – a negation of Einstein’s doubt that added up to positive support for his original idea.

Einstein didn’t see it that way. According to historical accounts, he was furious. He submitted the paper to another journal – the more obscure journal of the Franklin Institute in Philadelphia, not that anything with Einstein’s name on it could be obscure by that point in history. But before Einstein could reject his gravitational waves in that journal, Robertson indirectly nudged him to change his mind back again.

Robertson did this by becoming acquainted with one of Einstein’s assistants, Leopold Infeld, said Kennefick. It doesn’t appear that either Infeld or Einstein knew about Robertson’s role in rejecting the paper, as it’s traditional for reviewers to be anonymous. Robertson explained to Infeld why he thought Einstein was right the first time. That led to discussions between Einstein and Infeld, and before the paper came out, Einstein made radical revisions so that it supported rather than refuted the now famous forecast.

Who knows how history would have unfolded had Robertson let Einstein publish the original anti-gravitational-wave paper. It certainly helped to have Einstein on the favored side of things when it came to the difficult task of detection. The project that eventually led to a positive signal cost $1.1 billion over a period of 40 years. Called the Laser Interferometer Gravitational-Wave Observatory, or LIGO, it qualifies as the most expensive apparatus ever funded by the National Science Foundation.

The concept for LIGO was put forward by the MIT physicist Rainer Weiss back in 1972. The experiment is in the form of twin detectors, one near Hanford, Washington and one near Livingston, Louisiana. In each one, a laser beam travels down L-shaped pipes, each arm stretching two and a half miles. In theory, a gravitational wave would move mirrors at the ends of these pipes an inconceivably small distance that could be measured by the lasers.

The apparatus went through two iterations – a preliminary version that went up in 2010 and a more advanced version that went online in September of 2015. Within a few days of starting operation, the advanced detector registered something, which the physicists say fits the description of two black holes colliding.

The physicists say they can read a lot of information into the signal. They were able to discern the masses of the black holes - 29 and 36 times the mass of the sun - and a distance to the event of 1.3 billion light years from earth.

If they detect more collisions, the project could give scientists a more refined measure of distances to faraway objects and a better handle on the scale and expansion rate of the universe. They may observe other collisions between massive objects known as neutron stars, and learn about the nature of these exotic objects. And then there’s always the hope that they will find something completely unexpected.


The physicist who said no to Albert Einstein

NEW YORK – It takes a brave man to reject a scientific paper by Albert Einstein. But that’s what the physicist Howard Percy Robertson did in 1936, as editor of the journal Physical Review. Einstein was so enraged that he never published there again.

If Einstein were alive today, he might thank Robertson, who saved the great scientist from retracting the most far-reaching prediction of his theory of relativity — the existence of gravitational waves. The first direct detection of Einstein’s waves was announced last week to much fanfare and celebration. Scientists say the waves emanated from the powerful collision of two black holes.

The finding was hailed as a vindication, though Einstein was one of the biggest doubters of his own idea. He flip-flopped several times over the years, said physicist Daniel Kennefick, co-author of “An Einstein Encyclopedia.” The tale ended well, thanks to Einstein’s wisdom in knowing when to be sure, when to have doubts, when to ignore his doubters and when to listen to them and regroup.

The idea grew out of Einstein’s relativity theories. He published his special theory of relativity in 1905, changing the way scientists understood space and time. He published the general theory in 1915 and changed the way scientists understood gravity, redefining it as the effect of curves in space and time.

In February of 1916, Einstein predicted that if space and time could have lumps and bumps, then perhaps those bumps could move, said Kennefick. “After all, we can see moving hills and valleys on the surface of water that we call waves, so if gravity curves space-time, why couldn’t it create moving distortions?”

Einstein understood that these waves would be subtle. Only something dramatic could emit a signal strong enough to provide a chance to detect them — something like a merger of black holes. But Einstein was skeptical about the existence of black holes at all, even though others predicted them based on his theory.

These doubts didn’t mean that Einstein was insecure. He boldly predicted that the curve of space would produce a visible bending of starlight around the sun. That prompted the world’s best astronomers to see for themselves, waiting for a 1919 eclipse of the sun to make the behavior of faint light from background stars measurable. When asked how he’d feel if relativity was disproved by the eclipse experiment, Einstein famously replied: “Then I would feel sorry for the dear Lord. The theory is correct anyway.”

Einstein knew when to be certain, said Kennefick. He had a good physical intuition, and he also knew when he was ranging around in new territory.

So it’s perhaps understandable that he would at one point decide to quash his gravitational-wave prediction in a high profile journal article. In hindsight, one could see Robertson’s rejection as a double negative — a negation of Einstein’s doubt that added up to positive support for his original idea.

Einstein didn’t see it that way. According to historical accounts, he was furious. He submitted the paper to another journal — the more obscure journal of the Franklin Institute in Philadelphia, not that anything with Einstein’s name on it could be obscure by that point in history. But before Einstein could reject his gravitational waves in that journal, Robertson indirectly nudged him to change his mind back again.

Robertson did this by becoming acquainted with one of Einstein’s assistants, Leopold Infeld, said Kennefick. It doesn’t appear that either Infeld or Einstein knew about Robertson’s role in rejecting the paper, as it’s traditional for reviewers to be anonymous. Robertson explained to Infeld why he thought Einstein was right the first time. That led to discussions between Einstein and Infeld, and before the paper came out, Einstein made radical revisions so that it supported rather than refuted the now famous forecast.

Who knows how history would have unfolded had Robertson let Einstein publish the original anti-gravitational-wave paper. It certainly helped to have Einstein on the favored side of things when it came to the difficult task of detection. The project that eventually led to a positive signal cost $1.1 billion over a period of 40 years. Called the Laser Interferometer Gravitational-Wave Observatory, or LIGO, it qualifies as the most expensive apparatus ever funded by the National Science Foundation.

The concept for LIGO was put forward by the MIT physicist Rainer Weiss back in 1972. The experiment is in the form of twin detectors, one near Hanford, Washington state, and one near Livingston, Louisiana. In each one, a laser beam travels down L-shaped pipes, each arm stretching about 4 km. In theory, a gravitational wave would move mirrors at the ends of these pipes an inconceivably small distance that could be measured by the lasers.

The apparatus went through two iterations — a preliminary version that went up in 2010 and a more advanced version that went online in September of 2015. Within a few days of starting operation, the advanced detector registered something, which the physicists say fits the description of two black holes colliding.

The physicists say they can read a lot of information into the signal. They were able to discern the masses of the black holes — 29 and 36 times the mass of the sun — and a distance to the event of 1.3 billion light-years from Earth.

If they detect more collisions, the project could give scientists a more refined measure of distances to faraway objects and a better handle on the scale and expansion rate of the universe. They may observe other collisions between massive objects known as neutron stars, and learn about the nature of these exotic objects. And then there’s always the hope that they will find something completely unexpected.

Science writer Faye Flam is the author of “The Score: How the Quest for Sex has Shaped the Modern Man.”

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In Violation of Einstein, Black Holes Might Have ‘Hair’

According to Einstein’s general theory of relativity, black holes have only three observable properties: mass, spin and charge. Additional properties, or “hair,” do not exist.

Jonathan O⟊llaghan

Identical twins have nothing on black holes. Twins may grow from the same genetic blueprints, but they can differ in a thousand ways — from temperament to hairstyle. Black holes, according to Albert Einstein’s theory of gravity, can have just three characteristics — mass, spin and charge. If those values are the same for any two black holes, it is impossible to discern one twin from the other. Black holes, they say, have no hair.

“In classical general relativity, they would be exactly identical,” said Paul Chesler, a theoretical physicist at Harvard University. “You can’t tell the difference.”

Yet scientists have begun to wonder if the “no-hair theorem” is strictly true. In 2012, a mathematician named Stefanos Aretakis — then at the University of Cambridge and now at the University of Toronto — suggested that some black holes might have instabilities on their event horizons. These instabilities would effectively give some regions of a black hole’s horizon a stronger gravitational pull than others. That would make otherwise identical black holes distinguishable.

However, his equations only showed that this was possible for so-called extremal black holes — ones that have a maximum value possible for either their mass, spin or charge. And as far as we know, “these black holes cannot exist, at least exactly, in nature,” said Chesler.

But what if you had a near-extremal black hole, one that approached these extreme values but didn’t quite reach them? Such a black hole should be able to exist, at least in theory. Could it have detectable violations of the no-hair theorem?

A paper published late last month shows that it could. Moreover, this hair could be detected by gravitational wave observatories.

“Aretakis basically suggested there was some information that was left on the horizon,” said Gaurav Khanna, a physicist at the University of Massachusetts and the University of Rhode Island and one of the co-authors. “Our paper opens up the possibility of measuring this hair.”

In particular, the scientists suggest that remnants either of the black hole’s formation or of later disturbances, such as matter falling into the black hole, could create gravitational instabilities on or near the event horizon of a near-extremal black hole. “We would expect that the gravitational signal we would see would be quite different from ordinary black holes that are not extremal,” said Khanna.

If black holes do have hair — thus retaining some information about their past — this could have implications for the famous black hole information paradox put forward by the late physicist Stephen Hawking, said Lia Medeiros, an astrophysicist at the Institute for Advanced Study in Princeton, New Jersey. That paradox distills the fundamental conflict between general relativity and quantum mechanics, the two great pillars of 20th-century physics. “If you violate one of the assumptions [of the information paradox], you might be able to solve the paradox itself,” said Medeiros. “One of the assumptions is the no-hair theorem.”

The ramifications of that could be broad. “If we can prove the actual space-time of the black hole outside of the black hole is different from what we expect, then I think that is going to have really huge implications for general relativity,” said Medeiros, who co-authored a paper in October that addressed whether the observed geometry of black holes is consistent with predictions.

Perhaps the most exciting aspect of this latest paper, however, is that it could provide a way to merge observations of black holes with fundamental physics. Detecting hair on black holes — perhaps the most extreme astrophysical laboratories in the universe — could allow us to probe ideas such as string theory and quantum gravity in a way that has never been possible before.

“One of the big issues [with] string theory and quantum gravity is that it’s really hard to test those predictions,” said Medeiros. “So if you have anything that’s even remotely testable, that’s amazing.”

There are major hurdles, however. It’s not certain that near-extremal black holes exist. (The best simulations at the moment typically produce black holes that are 30% away from being extremal, said Chesler.) And even if they do, it’s not clear if gravitational wave detectors would be sensitive enough to spot these instabilities from the hair.

What’s more, the hair is expected to be incredibly short-lived, lasting just fractions of a second.

But the paper itself, at least in principle, seems sound. “I don’t think that anybody in the community doubts it,” said Chesler. “It’s not speculative. It just turns out Einstein’s equations are so complicated that we’re discovering new properties of them on a yearly basis.”

The next step would be to see what sort of signals we should be looking for in our gravitational detectors — either LIGO and Virgo, operating today, or future instruments like the European Space Agency’s space-based LISA instrument.

“One should now build upon their work and really compute what would be the frequency of this gravitational radiation, and understand how we could measure and identify it,” said Helvi Witek, an astrophysicist at the University of Illinois, Urbana-Champaign. “The next step is to go from this very nice and important theoretical study to what would be the signature.”

There are plenty of reasons to want to do so. While the chances of a detection that would prove the paper correct are slim, such a discovery would not only challenge Einstein’s theory of general relativity but prove the existence of near-extremal black holes.

“We would love to know if nature would even allow for such a beast to exist,” said Khanna. “It would have pretty dramatic implications for our field.”

Correction: February 11, 2021
The original version of this article implied that theorists are unable to simulate black holes closer than 30% away from being extremal. In fact, they can simulate near-extremal black holes, but their typical simulations are 30% away from being extremal.


How did we discover black holes?

Black holes unite some of the most buzzworthy topics in physics: Einstein’s theory of general relativity, quantum mechanics, the evolution of the universe (cosmology) and even religion.

The idea of a black hole was first conceived by a British, astronomy-minded clergyman named John Michell in the late 1700s. While mulling the discovery of stars that exist in binary (pairs) or triplets, Michell theorized that the gravitational forces of one star might affect light beaming from another.

This is not an actual image of a black hole. This artist’s impression depicts a rapidly spinning supermassive black hole surrounded by an accretion disc.
This thin disc of rotating material consists of the leftovers of a Sun-like star which was ripped apart by the tidal forces of the black hole. Shocks in the colliding debris as well as heat generated in accretion led to a burst of light, resembling a supernova explosion. Infographic and caption by European Southern Observatory, European Space Agency, M. Kornmesser

His thoughts extended the proposition to the extreme — a star so massive with so much gravitational pull that no light could escape, which he dubbed a “dark star.” French mathematician Pierre-Simon Laplace would arrive at the same theoretical conclusion a few years later the pair is often credited with origin of the concept.

Today, we know that black holes shape our universe. Recent research points to black holes sitting at the center of almost all large galaxies, including our very own Milky Way. Dijkgraaf said this evidence — and much more — points to black holes being essential to the structure of galaxies, if not the universe itself.

“There are many, many questions about how these black holes formed, particularly these gigantic black holes in the middle of galaxies.” Dijkgraaf said. “Are [supermassive black holes] the outcome of many smaller ones colliding, or were they baked in at the very beginning of our universe?”


John A. Wheeler, Physicist Who Coined the Term ‘Black Hole,’ Is Dead at 96

John A. Wheeler, a visionary physicist and teacher who helped invent the theory of nuclear fission, gave black holes their name and argued about the nature of reality with Albert Einstein and Niels Bohr, died Sunday morning at his home in Hightstown, N.J. He was 96.

The cause was pneumonia, said his daughter Alison Wheeler Lahnston.

Dr. Wheeler was a young, impressionable professor in 1939 when Bohr, the Danish physicist and his mentor, arrived in the United States aboard a ship from Denmark and confided to him that German scientists had succeeded in splitting uranium atoms. Within a few weeks, he and Bohr had sketched out a theory of how nuclear fission worked. Bohr had intended to spend the time arguing with Einstein about quantum theory, but “he spent more time talking to me than to Einstein,” Dr. Wheeler later recalled.

As a professor at Princeton and then at the University of Texas in Austin, Dr. Wheeler set the agenda for generations of theoretical physicists, using metaphor as effectively as calculus to capture the imaginations of his students and colleagues and to pose questions that would send them, minds blazing, to the barricades to confront nature.

Max Tegmark, a cosmologist at the Massachusetts Institute of Technology, said of Dr. Wheeler, “For me, he was the last Titan, the only physics superhero still standing.”

Under his leadership, Princeton became the leading American center of research into Einsteinian gravity, known as the general theory of relativity — a field that had been moribund because of its remoteness from laboratory experiment.

“He rejuvenated general relativity he made it an experimental subject and took it away from the mathematicians,” said Freeman Dyson, a theorist at the Institute for Advanced Study across town in Princeton.

Among Dr. Wheeler’s students was Richard Feynman of the California Institute of Technology, who parlayed a crazy-sounding suggestion by Dr. Wheeler into work that led to a Nobel Prize. Another was Hugh Everett, whose Ph.D. thesis under Dr. Wheeler on quantum mechanics envisioned parallel alternate universes endlessly branching and splitting apart — a notion that Bryce DeWitt, of the University of Texas in Austin, called “Many Worlds” and which has become a favorite of many cosmologists as well as science fiction writers.

Recalling his student days, Dr. Feynman once said, “Some people think Wheeler’s gotten crazy in his later years, but he’s always been crazy.”

John Archibald Wheeler — he was Johnny Wheeler to friends and fellow scientists — was born on July 9, 1911, in Jacksonville, Fla. The oldest child in a family of librarians, he earned his Ph.D. in physics from Johns Hopkins University at 21. A year later, after becoming engaged to an old acquaintance, Janette Hegner, after only three dates, he sailed to Copenhagen to work with Bohr, the godfather of the quantum revolution, which had shaken modern science with paradoxical statements about the nature of reality.

“You can talk about people like Buddha, Jesus, Moses, Confucius, but the thing that convinced me that such people existed were the conversations with Bohr,” Dr. Wheeler said.

Their relationship was renewed when Bohr arrived in 1939 with the ominous news of nuclear fission. In the model he and Dr. Wheeler developed to explain it, the atomic nucleus, containing protons and neutrons, is like a drop of liquid. When a neutron emitted from another disintegrating nucleus hits it, this “liquid drop” starts vibrating and elongates into a peanut shape that eventually snaps in two.

Two years later, Dr. Wheeler was swept up in the Manhattan Project to build an atomic bomb. To his lasting regret, the bomb was not ready in time to change the course of the war in Europe and possibly save his brother Joe, who died in combat in Italy in 1944.

Dr. Wheeler continued to do government work after the war, interrupting his research to help develop the hydrogen bomb, promote the building of fallout shelters and support the Vietnam War and missile defense, even as his views ran counter to those of his more liberal colleagues.

Dr. Wheeler was once officially reprimanded by President Dwight D. Eisenhower for losing a classified document on a train, but he also received the Atomic Energy Commission’s Enrico Fermi Award from President Lyndon B. Johnson in 1968.

When Dr. Wheeler received permission in 1952 to teach a course on Einsteinian gravity, it was not considered an acceptable field to study. But in promoting general relativity, he helped transform the subject in the 1960s, at a time when Dennis Sciama, at Cambridge University in England, and Yakov Borisovich Zeldovich, at Moscow State University, founded groups that spawned a new generation of gravitational theorists and cosmologists.

One particular aspect of Einstein’s theory got Dr. Wheeler’s attention. In 1939, J. Robert Oppenheimer, who would later be a leader in the Manhattan Project, and a student, Hartland Snyder, suggested that Einstein’s equations had made an apocalyptic prediction. A dead star of sufficient mass could collapse into a heap so dense that light could not even escape from it. The star would collapse forever while spacetime wrapped around it like a dark cloak. At the center, space would be infinitely curved and matter infinitely dense, an apparent absurdity known as a singularity.

Dr. Wheeler at first resisted this conclusion, leading to a confrontation with Dr. Oppenheimer at a conference in Belgium in 1958, in which Dr. Wheeler said that the collapse theory “does not give an acceptable answer” to the fate of matter in such a star. “He was trying to fight against the idea that the laws of physics could lead to a singularity,” Dr. Charles Misner, a professor at the University of Maryland and a former student, said. In short, how could physics lead to a violation itself — to no physics?

Dr. Wheeler and others were finally brought around when David Finkelstein, now an emeritus professor at Georgia Tech, developed mathematical techniques that could treat both the inside and the outside of the collapsing star.

At a conference in New York in 1967, Dr. Wheeler, seizing on a suggestion shouted from the audience, hit on the name “black hole” to dramatize this dire possibility for a star and for physics.

The black hole “teaches us that space can be crumpled like a piece of paper into an infinitesimal dot, that time can be extinguished like a blown-out flame, and that the laws of physics that we regard as ‘sacred,’ as immutable, are anything but,” he wrote in his 1999 autobiography, “Geons, Black Holes & Quantum Foam: A Life in Physics.” (Its co-author is Kenneth Ford, a former student and a retired director of the American Institute of Physics.)

In 1973, Dr. Wheeler and two former students, Dr. Misner and Kip Thorne, of the California Institute of Technology, published “Gravitation,” a 1,279-page book whose witty style and accessibility — it is chockablock with sidebars and personality sketches of physicists — belies its heft and weighty subject. It has never been out of print.

In the summers, Dr. Wheeler would retire with his extended family to a compound on High Island, Me., to indulge his taste for fireworks by shooting beer cans out of an old cannon.

He and Janette were married in 1935. She died in October 2007 at 99. Dr. Wheeler is survived by their three children, Ms. Lahnston and Letitia Wheeler Ufford, both of Princeton James English Wheeler of Ardmore, Pa. 8 grandchildren, 16 great-grandchildren, 6 step-grandchildren and 11 step-great-grandchildren.

In 1976, faced with mandatory retirement at Princeton, Dr. Wheeler moved to the University of Texas.

At the same time, he returned to the questions that had animated Einstein and Bohr, about the nature of reality as revealed by the strange laws of quantum mechanics. The cornerstone of that revolution was the uncertainty principle, propounded by Werner Heisenberg in 1927, which seemed to put fundamental limits on what could be known about nature, declaring, for example, that it was impossible, even in theory, to know both the velocity and the position of a subatomic particle. Knowing one destroyed the ability to measure the other. As a result, until observed, subatomic particles and events existed in a sort of cloud of possibility that Dr. Wheeler sometimes referred to as “a smoky dragon.”

This kind of thinking frustrated Einstein, who once asked Dr. Wheeler if the Moon was still there when nobody looked at it.

But Dr. Wheeler wondered if this quantum uncertainty somehow applied to the universe and its whole history, whether it was the key to understanding why anything exists at all.

“We are no longer satisfied with insights only into particles, or fields of force, or geometry, or even space and time,” Dr. Wheeler wrote in 1981. “Today we demand of physics some understanding of existence itself.”

At a 90th birthday celebration in 2003, Dr. Dyson said that Dr. Wheeler was part prosaic calculator, a “master craftsman,” who decoded nuclear fission, and part poet. “The poetic Wheeler is a prophet,” he said, “standing like Moses on the top of Mount Pisgah, looking out over the promised land that his people will one day inherit.” Wojciech Zurek, a quantum theorist at Los Alamos National Laboratory, said that Dr. Wheeler’s most durable influence might be the students he had “brought up.” He wrote in an e-mail message, “I know I was transformed as a scientist by him — not just by listening to him in the classroom, or by his physics idea: I think even more important was his confidence in me.”

Dr. Wheeler described his own view of his role to an interviewer 25 years ago.

“If there’s one thing in physics I feel more responsible for than any other, it’s this perception of how everything fits together,” he said. “I like to think of myself as having a sense of judgment. I’m willing to go anywhere, talk to anybody, ask any question that will make headway.

“I confess to being an optimist about things, especially about someday being able to understand how things are put together. So many young people are forced to specialize in one line or another that a young person can’t afford to try and cover this waterfront — only an old fogy who can afford to make a fool of himself.



The Discovery of Black Holes: From Theory to Actuality

The black hole named Cygnus X-1 pulls matter from the super giant blue star near it. (Image:NASA-CXC-M.Weiss/www.nasa.gov)

Einstein Dismisses Black Holes

Although astronomers and physicists had learned much about stars in the fifteen years since the discovery of general relativity—including the likely existence of white dwarfs and neutron stars—Albert Einstein’s opinions on the subject had not changed substantially.

In 1939, he wrote his first and only paper about black holes, entitled “On a Stationary System with Spherical Symmetry Consisting of Many Gravitating Masses.” In this article, Einstein set out to calculate how a large group of particles would behave as they collapsed under the force of gravity.

This is a transcript from the video series What Einstein Got Wrong. Watch it now, on Wondrium.

Albert Einstein’s opinion that black holes could never exist in nature led most physicists specializing in relativity to dismiss all talk of black holes for many years. (Image: Doris Ulmann/Public domain)

Einstein argued that the particles’ angular momentum would prevent them from collapsing indefinitely and that this would prevent a black hole from ever forming. In this conclusion, he was completely wrong.

Einstein’s prejudice that black holes could never exist in nature blinded him from all of the arguments to the contrary, leading him to reject one of the most incredible facets of his theory.

Worse still, Einstein’s opinion was so highly regarded that most physicists specializing in relativity tended to dismiss all talk of black holes for many years afterward. For decades, such objects were seldom mentioned in scientific literature.

Furthermore, interest in general relativity declined considerably during this period. It wasn’t so much that physicists doubted the validity of Einstein’s theory they simply hadn’t found many practical uses for it.

The predictions made by general relativity are, in most cases, similar to the old Newtonian predictions. There wasn’t much that could be done in a laboratory either to test the theory further or explore its implications.

General Relativity’s Renaissance

A few years after Einstein’s death in 1955, interest in general relativity began to see a resurgence. All around the world, small groups of physicists started to actively explore the deeper—and stranger—implications of Einstein’s general theory.

One of the key figures in general relativity’s renaissance was the young British physicist and mathematician, Roger Penrose. Penrose first became interested in relativity while he was an undergraduate at University College London.

During this period, however, few physicists knew very much about general relativity. Penrose had little choice but to teach himself about the subject, managing to learn general relativity from books and papers instead of from his professors.

Penrose then went on to study mathematics at Cambridge, where he earned his Ph.D., and then researched for brief stints at Princeton, London, Syracuse and the University of Texas at Austin.

At the time, Austin was the location of one of the few concentrations of physicists who were actively studying general relativity. Among others, Penrose met the physicist Roy Kerr in Austin.

Kerr was able to find a solution to Einstein’s field equations that is more general and more powerful than those found by Karl Schwarzschild. In particular, while Schwarzschild’s result only describes stationary objects, Kerr’s solution also allows for the possibility that black holes could be rotating.

Proving the Existence of Black Holes

British physicist and mathematician Roger Penrose proved that under certain circumstances, a collapsing star would be guaranteed to form a black hole. (Image: Biswarup Ganguly/Public domain)

At the time, few physicists thought that black holes genuinely existed—if they gave any thought to the matter at all. But in 1965, Penrose made a discovery that would upend that viewpoint.

Using a type of mathematics that was very different from anything Einstein had ever used, Penrose was able to rigorously prove that, under certain circumstances, a collapsing star would be guaranteed to form a black hole. In particular, if the collapsing star is massive enough, then the formation of a black hole is entirely inevitable.

In January of 1965, Penrose published a short, three-page paper, entitled “Gravitational Collapse and Space-Time Singularities.” At the time, Penrose’s argument went strongly against the conventional wisdom of the physics community.

Many argued, as Einstein had long done, that the complexities of real collapsing stars would prevent them from forming black holes.

But Penrose’s mathematical argument was compelling. Over the next few years, the opinions of many physicists were swayed. By the end of the 1960s, it had become a mainstream view that black holes were, in fact, likely—if not guaranteed—to exist in nature.

How Black Holes Affect Surrounding Stars

As more and more physicists became convinced that black holes exist, interest began to grow about the ways that these objects might be detected or observed. One of the first scientists to actively work on this question was the incredibly prolific and versatile Russian physicist Yakov Zel’dovich.

Throughout his career, Zel’dovich made major contributions to almost every field of physics and astronomy, including material science, particle physics, relativity, astrophysics, cosmology, and nuclear physics—including work that he did on the Soviet weapons program.

Russian physicist Yakov Zel’dovich proposed that a black hole can be detected by studying the motion of nearby stars. (Image: MARKA Publishing & Trading Centre/Public domain)

In the early 1960s, Zel’dovich proposed that the presence of black holes could be indirectly inferred by studying the motion of other nearby stars. The invisible black hole, he argued, would cause another star within its own solar system to wobble back and forth with a regular period.

If scientists could somehow observe such a wobbling star, they could identify the black hole, and even measure its mass.

Alternatively, Zel’dovich argued that under certain circumstances, a black hole could have a dramatic impact on the material surrounding it. All astrophysical bodies attract and accumulate matter through the force of their gravity.

But unlike ordinary stars or planets, the matter that falls toward a black hole will be accelerated to nearly the speed of light as it approaches. Furthermore, this infalling material will spiral around the black hole like a fluid running down a drain.

Since this material moves at nearly the speed of light, it reaches temperatures in the millions of degrees. Zel’dovich argued that such systems would release huge amounts of energy and could be observed by astronomers, even at very great distances.

The Mystery of Cygnus X-1

The mystery of the strange astronomical object known as Cygnus X-1 left astronomers perplexed. First detected by astronomers in 1964, observations of this object in 1970, however, revealed some of its more bizarre characteristics.

Cygnus X-1 was observed to release very bright flashes of X-rays multiple times each second. The short duration of this X-ray light indicated that whatever was emitting them was not very big by astronomical standards—no more than a fraction of a light second across.

In other words, the object would be no more than 100,000 kilometers or so. X-rays are produced only in very hot environments at millions of degrees.

In the following year, radio observations in the direction of Cygnus X-1 discovered a blue supergiant star. This star, however, is far too big to generate the rapid X-ray flickering that had been observed.

To explain the production of the observed X-rays, astronomers deduced that a portion of this star’s gas was somehow being torn off, then heated to very high temperatures. Later in the same year, other observations began to detect the wobble of the blue supergiant—just as Zel’dovich had suggested a decade earlier.

From the observed wobble, it was clear to astronomers that the nearby object was massive—far too massive to even be a neutron star.

As the quality of the observations continued to improve over the years that followed, it became clearer that Cygnus X-1 was a black hole. By the late 1970s, most astrophysicists had come to accept this conclusion, as well as the conclusion that black holes indeed exist in our universe.

Cygnus X-1, a black hole about 6000 light years away from us (right) sucks gas from the nearby super giant star named HDE 226868. (30 times the mass of our Sun) (Image : ESA-Hubble/www.nasa.gov)

It is now known that Cygnus X-1 is a black hole about 6,000 light-years away from us, and about 15 times as massive as the Sun. At this mass, the Schwarzschild radius of this black hole is about 44 kilometers.

Anything within this radius is forever lost from our view. And, in a sense, is lost from our universe itself.

The Black Holes Around Us

In the decades following the determination that Cygnus X-1 is a black hole, astronomers and astrophysicists discovered numerous other black holes in our universe. This includes dozens of black holes that were once thought to be massive stars, similar to Cygnus X-1.

Also, many larger and more massive black holes have been discovered. The center of the Milky Way galaxy, for example, is the host of an enormous black hole, with a mass equal to about four million times the mass of the Sun.

The center of our own Milky Way galaxy hosts an enormous black hole, with a mass equal to about four million times the mass of the Sun. (Image: ESA–C. Carreau/www.nasa.gov)

It is now generally thought that most spiral and elliptical galaxies contain a supermassive black hole at their centers.

Although most of these supermassive black holes are similar in mass to the one at the center of the Milky Way, some galaxies harbor even larger black holes, with masses that are measured in the billions, rather than mere millions, of solar masses.

Black holes are a consequence of Einstein’s Theory of General Relativity. Yet Einstein never came to accept that black holes did—or even could—exist in our universe.

Common Questions About the Discovery of Black Holes

Even though Einstein’s general relativity predicted black holes , Karl Schwarzschild is often credited with discovering them. Even this fact is tricky to state with absolute certainty, though, as Kerr after him better defined what black holes were. It was Roger Penrose who proved their existence as collapsed stars.

Scientists estimate that nearly all large galaxies have super massive black holes in their center, which would result in billions of billions.

Yes. Scientists have confirmed a super massive black hole at the center of the Milky Way.

Scientists believe that when a galaxy forms, its black hole is formed at the same time.


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