Stephen Hawking's most famous prediction could mean that everything in the universe is doomed to evaporate, new study says

An artist's illustration of three black holes merging.
An artist's illustration of three black holes merging. (Image credit: Shutterstock)

Stephen Hawking's most famous theory about black holes has just been given a sinister update — one that proclaims that everything in the universe is doomed to evaporate.

In 1974, Hawking proposed that black holes eventually evaporate by losing what's now known as Hawking radiation — a gradual draining of energy in the form of light particles that spring up around black holes' immensely powerful gravitational fields. Now, a new update to the theory has suggested that Hawking radiation isn't just created by stealing energy from black holes, but from all objects with enough mass.

If the theory is true, it means that everything in the universe will eventually disappear, its energy slowly bled from it in the form of light. 

Related: Lab-grown black hole may prove Stephen Hawking's most challenging theory right

"That means that objects without an event horizon [the gravitational point of no return beyond which nothing, not even light, can escape a black hole], such as the remnants of dead stars and other large objects in the universe, also have this sort of radiation," lead author Heino Falcke, a professor of astrophysics at Radboud University in the Netherlands, said in a statement. "And, after a very long period, that would lead to everything in the universe eventually evaporating, just like black holes. This changes not only our understanding of Hawking radiation but also our view of the universe and its future."

The researchers published their findings June 2 in the journal Physical Review Letters.

Space-time monsters

According to quantum field theory, there is no such thing as an empty vacuum. Space is instead teeming with tiny vibrations that, if imbued with enough energy, randomly burst into virtual particles, producing very-low-energy packets of light, or photons.

In a landmark paper published in 1974, Hawking famously predicted that the extreme gravitational force felt at the mouths of black holes — their event horizons — would summon photons into existence in this way. Gravity, according to Einstein's theory of general relativity, distorts space-time, so that quantum fields get more warped the closer they get to the immense gravitational tug of a black hole's singularity.

Because of the uncertainty and weirdness of quantum mechanics, Hawking said this warping creates uneven pockets of differently moving time and subsequent spikes of energy across the field. These energy mismatches make photons appear in the contorted space around black holes, siphoning energy from the black hole's field so they can burst into existence. If the particles then escape the black hole, this energy theft led Hawking to conclude that — over a vast timescale much longer than the current age of the universe — black holes would eventually lose all of their energy and disappear completely.

But if a gravitational field is all that's needed to produce quantum fluctuations and photons, what's stopping any object with a space-time warping mass from creating Hawking radiation? Does Hawking radiation need the special condition of a black hole's event horizon, or can it be produced anywhere in space? To probe these questions, the authors of the new study analyzed Hawking radiation through the lens of a long-predicted process called the Schwinger effect, in which matter can theoretically be generated from the powerful distortions caused by an electromagnetic field.

Sure enough, by applying the framework of the Schwinger effect to Hawking's theory, the theoretical physicists produced a mathematical model that reproduced Hawking radiation in spaces experiencing a range of gravitational field strengths. According to their new theory, an event horizon isn't necessary for energy to slowly leak from a massive object in the form of light; the object's gravitational field is good enough on its own.

"We show that far beyond a black hole the curvature of space-time plays a big role in creating radiation," second author Walter van Suijlekom, a professor of mathematics at Radboud University, said in the statement. "The particles are already separated there [beyond the black hole] by the tidal forces of the gravitational field."

What the researchers' theory means in reality isn't clear. Possibly, as the matter that makes up stars, neutron stars, and planets ages, it will eventually undergo an energy transition into a completely new ultralow energy state. This might be enough to eventually collapse all matter into black holes, which could continue to slowly drip out light until they too disappear without a trace.

Unfortunately (or fortunately, depending on any misgivings you may have about evaporating), all of this is just speculation awaiting confirmation. To figure out if it's a true prediction of our universe's eventual fate, physicists will need to spot some Hawking radiation being produced around gravitationally dense objects — both around black holes and planets, stars, or neutron stars. If everything is destined to disappear in a flash of cool light, there should be plenty of places to look.

Ben Turner
Staff Writer

Ben Turner is a U.K. based staff writer at Live Science. He covers physics and astronomy, among other topics like tech and climate change. He graduated from University College London with a degree in particle physics before training as a journalist. When he's not writing, Ben enjoys reading literature, playing the guitar and embarrassing himself with chess.

  • a2+b2=c2
    To quote Scarlett O’Hara … “I’ll worry about that tomorrow.”
  • Johnnyreddogg
    Why does the future always have to end in some cataclysm? This really isn't one of those disaster movies. The universe is not going to decay and evaporate. We heard about the universe contracting for how many decades? And then we found out that it really is expanding. We heard about the big bang and how everything generated from that point of explosion for lack of a better word. Now, we know that there is no center of the universe.

    But the universe and so many examples in nature that we are aware of, duplicates itself on different scales. Single atoms are like a small solar system or with gravity and everything. Galaxies are like massive solar systems, and on a larger scale, the universe is partitioned off into groups of galaxies that function in the same manner as a solar system or maybe an atom.

    On earth, moons and planets in our solar system, they are volcanically active, recycle. On Earth, we know that tectonic mantle plates actually subducts underneath other plates. That subduction zone forces ocean water and ocean sediment deep into the earth. Some of it turns into magma again to be recycled through volcanic activity. This creates new land mass and Islands in the oceans.

    Nature repeats this with black holes, they are absorbing light and matter. And we know that light can be turned into matter. The black holes excrete matter which forms new stars and more than likely galaxies. The black holes are the subduction zones of the universe. They suck up the dead and dying debris and recycle it into matter.

    This engine will continue on to infinity. And whatever the edges of the universe are, they will continue to expand. The areas expanding between galaxies will be filled eventually by new and burgeoning formations. All of this driven by what we call black holes and their recycling prowess. It functions exactly the same as the recycling process of the tectonic plates and volcanic activity on Earth.
  • donone101
    Our knowledge of the universe and what makes it tick is 'subject to change' the smarter we get. Of course science writers need to create tantalizing headlines, as is the case on this piece, to entice the curious to read further. It's truly an extension of the old sci-fi stuff many of us spent many a sleepless night as kids, reading ever more about those mysterious worlds 'out there' and the writers' ideas about how we could get there.

    I am continually fascinated by the evolving theories regarding the makeup of the universe, where it came from and where it's going, and how humans fit into it all. AI will at some point speed up the process to help us make sense of dangling theories that await further understanding, while in the process adding ever more avenues to research. The exciting part of this process is that the more we learn, the more questions we have.

    Imagining the universe as an infinite entity whose current age is speculated to be "X" billions of years old needs to be offset by understanding how old we humans are in context! How comically naive it is to imagine that we are much past glimpsing the first page or two of the (from our current perspective) book of knowledge on this subject.
  • Johnnyreddogg
    donone101 said:
    Our knowledge of the universe and what makes it tick is 'subject to change' the smarter we get. Of course science writers need to create tantalizing headlines, as is the case on this piece, to entice the curious to read further. It's truly an extension of the old sci-fi stuff many of us spent many a sleepless night as kids, reading ever more about those mysterious worlds 'out there' and the writers' ideas about how we could get there.

    I am continually fascinated by the evolving theories regarding the makeup of the universe, where it came from and where it's going, and how humans fit into it all. AI will at some point speed up the process to help us make sense of dangling theories that await further understanding, while in the process adding ever more avenues to research. The exciting part of this process is that the more we learn, the more questions we have.

    Imagining the universe as an infinite entity whose current age is speculated to be "X" billions of years old needs to be offset by understanding how old we humans are in context! How comically naive it is to imagine that we are much past glimpsing the first page or two of the (from our current perspective) book of knowledge on this subject.
    Excellent and very thoughtful insight concerning the thread. I agree wholeheartedly with this comment and your opinion in general.
  • Epicenter & 4 more
    I don't believe in anything fading, evaporating from Hawkin's radiation, I won't consider this until having an explanation for why this 'Split particle' radiation events is not detected in other bodies.
    Saturn has no 'event horizon' but has a gravity field.
    Gesund +
  • LaraK
    Are we really considering this new this is like a guy who really needs to get a paper published so he's like "okay it's heat death but make it quirky!"

    Physicist and astrophysicists need to look at themselves and say is the thing that I'm researching productive. Will it be useful in the next hundred years. Will it matter in the next hundred years.

    I think a lot of them if they ask themselves that would have to say no and that's never been the case. Tycho brahe is writing down the position of everything hes seen he knows that's going to be useful. When Mendel is doodling a bunch of squares trying to figure out how to describe genes he knows that's useful.

    How is it useful to have this theory? It's not even motivating any research that wouldn't already be motivated by something more tangible.
  • Hartmann352
    Everywhere in space-time, pairs of “virtual” particles are constantly arising and mutually annihilating.
    Virtual particles are indeed real particles. Quantum theory predicts that every particle spends some time as a combination of other particles in all possible ways. These predictions are very well understood and tested.

    Quantum mechanics allows, and indeed requires, temporary violations of conservation of energy, so one particle can become a pair of heavier particles (the so-called virtual particles), which quickly rejoin into the original particle as if they had never been there. If that were all that occurred we would still be confident that it was a real effect because it is an intrinsic part of quantum mechanics, which is extremely well tested, and is a complete and tightly woven theory--if any part of it were wrong the whole structure would collapse.

    But while the virtual particles are briefly part of our world they can interact with other particles, and that leads to a number of tests of the quantum-mechanical predictions about virtual particles. The first test was understood in the late 1940s.

    In a hydrogen atom an electron and a proton are bound together by photons (the quanta of the electromagnetic field). Every photon will spend some time as a virtual electron plus its antiparticle, the virtual positron, since this is allowed by quantum mechanics as described above. The hydrogen atom has two energy levels that coincidentally seem to have the same energy. But when the atom is in one of those levels it interacts differently with the virtual electron and positron than when it is in the other, so their energies are shifted a tiny bit because of those interactions. That shift was measured by Willis Lamb and the Lamb shift was born, for which a Nobel Prize was eventually awarded.

    Quarks are particles much like electrons, but different in that they also interact via the strong force. Two of the lighter quarks, the so-called "up" and "down" quarks, bind together to make up protons and neutrons. The "top" quark is the heaviest of the six types of quarks. In the early 1990s it had been predicted to exist but had not been directly seen in any experiment. At the LEP collider at the European particle physics laboratory CERN, millions of Z bosons--the particles that mediate neutral weak interactions--were produced and their mass was very accurately measured. The Standard Model of particle physics predicts the mass of the Z boson, but the measured value differed a little. This small difference could be explained in terms of the time the Z spent as a virtual top quark if such a top quark had a certain mass. When the top quark mass was directly measured a few years later at the Tevatron collider at Fermi National Accelerator Laboratory near Chicago, the value agreed with that obtained from the virtual particle analysis, providing a dramatic test of our understanding of virtual particles.

    Another very good test some readers may want to look up is the Casimir effect, where forces between metal plates in empty space are modified by the presence of virtual particles.

    Thus virtual particles are indeed real and have observable effects that physicists have devised ways of measuring. Their properties and consequences are well established and well understood consequences of quantum mechanics.

    Stephen Hawking realized that when these pairs arise straddling the horizon of a black hole, one virtual particle will get sucked in while its partner escapes, preventing their mutual destruction. The escaped particle becomes real, stealing the energy needed for the upgrade from the black hole’s gravitational field. Meanwhile the in-falling particle acquires negative energy, lowering the energy of the black hole.

    Thus, one radiated particle at a time, the black hole blinks out of existence, ultimately leaving no trace: Hawking’s calculation indicated that the radiation is “thermal,” consisting of a featureless, random spread of energies that encodes no details about the collapsed star that formed the black hole, or about anything else of interest that might have fallen in.

    According to quantum mechanics, the probabilities of all possible states of particles in the universe must respect “unitarity,” evolving in such a way that the universe’s past states can in principle always be uniquely determined by rewinding from its present state. But if information is lost when a black hole evaporates into a featureless gas of Hawking radiation, then the universe’s past can’t be gleaned from the present, and quantum mechanics breaks down.

    Or perhaps Hawking erred.

    To do his calculation, he made a key assumption: that space-time is smooth and continuous at the horizon of a black hole, as described by general relativity. Physicists believe that this is an approximation; zoom in far enough on Einstein’s space-time continuum, and a more fundamental, quantum form of gravity emerges. But whereas quantum gravity surely becomes important near a black hole’s super-dense center, known as its “singularity,” Hawking assumed that he could gloss over this short-distance physics in his description of quantum fluctuations at the horizon, where gravity is comparatively mild. According to general relativity, the slope of space-time is gentle enough at the horizon of a typical supermassive black hole (like those at the centers of many galaxies) that an astronaut floating past it wouldn’t even notice.

    In 1981, Unruh discovered that Hawking’s approximation scheme can also be applied to fluids. Like space-time, fluids appear continuous on large scales even though deep down they’re made of discrete atoms. Unruh showed that, just as pairs of particles fluctuate in and out of space-time, vibrations called “phonons,” the quantum units of sound, should surface throughout fluids. And when pairs of phonons arise near the sonic horizon of a sonic black hole, they should get wrenched apart and rendered permanent, producing the sonic analogue of Hawking radiation.

    This is the phenomenon that Jeff Steinhauer reported in August in Nature Physics, after toiling over his experiment since 2009 — “exclusively, all day every day,” he said. He created an exotic fluid called a “Bose-Einstein condensate” out of super-cooled rubidium atoms. He then got it flowing, and zapped the fluid partway along its flow path with a laser, accelerating it to a supersonic speed and creating a sonic horizon. Finally, Steinhauer measured quantum entanglement between pairs of phonons on either side of this horizon, consistent with sonic Hawking radiation.

    The finding confirms that the fluid approximation works in the case of sonic black holes. “The question is, how related are the approximations?” said Stephan Hartmann, a philosopher of physics at Ludwig Maximilian University in Munich, Germany. If sonic black holes serve as a true analogue, then Hawking’s approximation is correct, the event horizon is an uneventful place, and information gets destroyed in black holes, meaning that the probabilistic rules of quantum mechanics must be replaced by a more fundamental framework. If Hawking’s approximation is wrong, then sonic black holes are not good proxies for black holes, and quantum gravity might somehow encode black hole histories in their radiation, preserving information as black holes evaporate.

    Unruh believes Hawking’s approximation is correct. In 2005, he and Ralf Schützhold of the University of Duisburg-Essen in Germany showed that Hawking radiation consistently came out as a robust theoretical prediction in both sonic black holes and actual black holes, no matter what theoretical assumptions they made about the details of the short-distance physics. The small-scale properties of space-time or fluids never affected the outcome of the calculation, suggesting that Hawking’s approximation wasn’t glossing over anything important. Unruh interprets this to mean that effects from quantum gravity aren’t capable of modifying Hawking radiation and rescuing information. In his opinion, Steinhauer’s result adds to the evidence that “this thermal radiation is a really robust phenomenon,” and thus, that “information is lost.”

    However, most quantum gravity researchers believe that information is preserved — including Hawking, who switched camps in the 2000s. From their perspective, an analogue to Hawking radiation in sonic black holes says nothing about true black holes because the two are categorically different; whereas the fluid approximation is accurate in the case of sonic black holes, space-time must not be approximately smooth at black hole event horizons. Somehow, quantum gravity modifies horizons — and it must do so in an extreme way, to get around Unruh and Schutzhold’s argument about the robustness of Hawking radiation. “We are in the situation where something big has to give,” Bousso said. “But we still don’t know exactly what to replace general relativity with at the horizon.”

    Some thought experiments suggest that black holes might be empty shells that carry all their information plastered on their horizons and project it outward to the rest of the universe like holograms. In that case, falling into a black hole would be less like a fish plunging over a waterfall and more like a bug going splat on a window.

    In the majority opinion, the comparison with sonic black holes only reinforces how strange black holes and the theory of quantum gravity must be. Harlow, who takes this view, sees sonic black holes not as black hole analogues, but more like computer simulations that are running the wrong equations. If you were to simulate the equations of quantum gravity, “then I do expect you to find the right answer,” he said. “Currently, I don’t know which equations to give you.”

    See: new particles around black holes with gravitational waves
    by Staff Writers
    Amsterdam. Netherlands (SPX)
    Jun 08, 2022

    Clouds of ultralight particles can form around rotating black holes. A team of physicists from the University of Amsterdam and Harvard University now show that these clouds would leave a characteristic imprint on the gravitational waves emitted by binary black holes.

    Black holes are generally thought to swallow all forms of matter and energy surrounding them. It has long been known, however, that they can also shed some of their mass through a process called superradiance. While this phenomenon is known to occur, it is only effective if new, so far unobserved particles with very low mass exist in nature, as predicted by several theories beyond the Standard Model of particle physics.

    Ionizing gravitational atoms
    When mass is extracted from a black hole via superradiance, it forms a large cloud around the black hole, creating a so-called gravitational atom. Despite the immensely larger size of a gravitational atom, the comparison with sub-microscopic atoms is accurate because of the similarity of the black hole plus its cloud with the familiar structure of ordinary atoms, where clouds of electrons surround a core of protons and neutrons.

    In a publication that appeared in Physical Review Letters this week, a team consisting of UvA physicists Daniel Baumann, Gianfranco Bertone, and Giovanni Maria Tomaselli, and Harvard University physicist John Stout, suggest that the analogy between ordinary and gravitational atoms runs deeper than just the similarity in structure. They claim that the resemblance can in fact be exploited to discover new particles with upcoming gravitational wave interferometers.

    In the new work, the researchers studied the gravitational equivalent of the so-called 'photoelectric effect'. In this well-known process, which for example is exploited in solar cells to produce an electric current, ordinary electrons absorb the energy of incident particles of light and are thereby ejected from a material - the atoms 'ionize'.

    In the gravitational analogue, when the gravitational atom is part of a binary system of two heavy objects, it gets perturbed by the presence of the massive companion, which could be a second black hole or a neutron star. Just as the electrons in the photoelectric effect absorb the energy of the incident light, the cloud of ultralight particles can absorb the orbital energy of the companion, so that some of the cloud gets ejected from the gravitational atom.

    Finding new particles
    The team demonstrated that this process may dramatically alter the evolution of such binary systems, significantly reducing the time required for the components to merge with each other. Moreover, the ionization of the gravitational atom is enhanced at very specific distances between the binary black holes, which leads to sharp features in the gravitational waves that we detect from such mergers.

    Future gravitational wave interferometers - machines similar to the LIGO and Virgo detectors that over the past few years have shown us the first gravitational waves from black holes - could observe these effects. Finding the predicted features from gravitational atoms would provide distinctive evidence for the existence of new ultralight particles.

    In the realist particle narrative, virtual particles pop up when observable particles get close together. They are emitted from one particle and absorbed by another, but they disappear before they can be measured. They transfer force between ordinary particles, giving them motion and life. For every different type of elementary particle (quark, photon, electron, etc.), there are also virtual quarks, virtual photons, and so on.

    In the opposing narrative, virtual particles are not real and show up only in the mathematical theories and equations of quantum physics, which describe the particle world. The equations are correct, the doubters recognize, predicting all sorts of things like the peculiar magnetic properties of electrons and muons.

    But the entities called virtual particles are just parts of the math, it is claimed. Virtual particles have never been and cannot be directly observed, by their mathematical definition. They supposedly pop up only during fleeting particle interactions.

    Hawking radiation describes hypothetical particles formed by a black hole 's boundary. This radiation implies black holes have temperatures that are inversely proportional to their mass. Putting it another way, the smaller a black hole is, the hotter it should glow.