Gravitational waves hint at a 'supercool' secret about the Big Bang
Scientists might be on track to revealing new facets of physics.
![Two overlapping groups of orange and red concentric circles](https://cdn.mos.cms.futurecdn.net/6845AZoHLoaX3axjAeAKP3-320-80.png)
In 2023, physicists were awed to find nearly imperceptible ripples in the fabric of space and time — united as an entity known as spacetime. They were ripples discovered in association with collections of rapidly spinning neutron stars called "pulsar timing arrays."
This low-frequency background hum of gravitational waves in our universe was originally attributed to a change, or a "phase transition," that occurred shortly after the Big Bang. New research, however, casts doubt on that assumption.
"Theorists and experimentalists have speculated nanohertz gravitational waves originated from a known transition that happened very soon after the Big Bang — a change that generated the masses of all the known fundamental particles," Andrew Fowlie, an assistant professor at Xi'an Jiaotong-Liverpool University, said in a statement. "However, our work uncovers serious problems with that otherwise appealing explanation of their origin."
Phase transitions are sudden changes in a substance's properties, and they typically occur when a particular substance reaches a critical temperature. The phase transition perhaps most familiar to us is the transition of water into ice as temperatures fall below freezing. There are also what are known as "supercool" transitions. With water, a supercool transition occurs when the substance gets "stuck" in its liquid phase, slowing its transformation into ice.
Many scientists believe a "first-order phase transition" occurred at the very beginning of time, triggering the launch of gravitational waves, or ripples in space-time. Those waves, experts think, could therefore be used to determine conditions present during the first epoch of rapid inflation in our universe, or maybe even the conditions present before the Big Bang.
Just a phase?
The concept of gravitational waves dates back to Albert Einstein's 1915 theory of gravity called "general relativity." The great physicist's magnum opus theory predicts that objects with mass have a warping effect on the very fabric of spacetime . Our physical experience of gravity, the theory states, arises from this warping.
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General relativity goes further than this as well, also suggesting that when objects accelerate, they generate ripples in spacetime — aka, gravitational waves. Though this phenomenon is negligible when it comes to the acceleration of objects on a scale we see on Earth, the effect becomes significant when the acceleration involves massive cosmic objects like supermassive black holes and neutron stars.
For instance, when these objects exist in binary systems — meaning two of them constantly accelerate around one another — they continuously emit gravitational waves until they finally collide and emit a high-pitched "screech" of these ripples.
Additionally, gravitational waves, like electromagnetic radiation, come in a range of frequencies. High-frequency gravitational waves, like high-frequency light, have shorter wavelengths and are more energetic; low-frequency gravitational waves have longer wavelengths and are less energetic. Low-frequency longwave gravitational waves also have long "periods," which refers to the time between one peak of the wave passing a set point to the next peak passing that point.
The gravitational waves detected by the North American Nanohertz Observatory for Gravitational Waves (NANOGrav) pulsar timing array in June 2023 are lower in frequency than the gravitational waves seen coming from supermassive black hole and neutron star mergers routinely detected by the Laser Interferometer Gravitational-Wave Observatory (LIGO), VIRGO,and KAGRA.
This means there must be a different source for these low-frequency nanohertz gravitational waves. The prime suspect? A phase transition just after the Big Bang — a supercool one, to be exact.
"We found that to have created waves with such tiny frequencies, the transition would have to be supercool," Fowlie explained.
However, there is a problem. Such cosmic supercool transition phases would be a bit unexpected during the period of rapid cosmic inflation (in other words, the universe's expansion) triggered by the Big Bang.
"These slow transitions would struggle to finish, as the transition rate is slower than the cosmic expansion rate of the universe," Fowlie said. "What if the transition sped up at the end? We calculated that even if this helped the transition to end, it would shift the frequency of the waves away from nanohertz."
The researcher also added that, although nanohertz gravitational waves are cool, they are probably not "supercool" in origin.
"If these gravitational waves do come from first-order phase transitions, we now know that there must be some new, much richer physics going on — physics we don't know about yet," Fowlie said.
Fowlie and colleagues believe their research demonstrates that more care is needed to understand supercool phase transitions, especially those that could have occurred at the beginning of the universe.
"Because these are necessarily slow transitions, the usual simplifications of whether transitions complete or not won't work," he said. "There are a lot of subtleties in the connections between the energy scale of the transitions and the frequency of the waves, so we need more careful and sophisticated techniques when considering gravitational waves and supercool transitions.
"Understanding this field will help us understand the most fundamental questions about the origin of the universe."
A better comprehension of supercool phase transitions could also help understand more Earthly and less cosmic phase transitions.
"It also has links to applications that are closer to home, such as understanding how water flows through a rock, the best ways to percolate coffee, and how wildfires spread," Fowlie concluded.
The team's research is discussed in a paper published in the journal Physical Review Letters.
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Robert Lea is a science journalist in the U.K. whose articles have been published in Physics World, New Scientist, Astronomy Magazine, All About Space, Newsweek and ZME Science. He also writes about science communication for Elsevier and the European Journal of Physics. Rob holds a bachelor of science degree in physics and astronomy from the U.K.’s Open University. Follow him on Twitter @sciencef1rst.
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Unclear Engineer I thought "supercool" phase transitions were quite rapid. At least for water that is supercooled, a disturbance of some sort seems to trigger the whole volume to go from liquid to solid state much more rapidly than if the ice freezes from the water at its normal freezing point. I though that had to do with the internal energy being lower, so that not as much of it needs to be "lost" by some sort of radiative or conductive process in order for the phase change to not be slowed by the energy passing though the water.Reply -
Torbjorn Larsson The prime suspect for the NANOGrav observations was stated by the collaboration in their evidence paper:Reply
The inferred gravitational-wave background amplitude and spectrum are consistent with astrophysical expectations for a signal from a population of supermassive black hole binaries, although more exotic cosmological and astrophysical sources cannot be excluded.
The phase transition from which looks like a slow roll scalar field is often thought to have been a second order one, explaining the current absence of different Higgs vacuum bubbles and domain walls. (It was followed by a second QCD phase transition, but the rapid expansion is believed to have pushed it directly into a QCD plasma state.)
OHdUFPAK7f0View: https://www.youtube.com/watch?v=OHdUFPAK7f0
It is possible that weak, vanishing domain walls would have generated a smidgen primordial gravitational waves, but we don't seem to be able to see them. -
Unclear Engineer After watching the video, it seems that the thinking and the terminology keep changing, and are not actually a generalized consensus among just about all researchers. But, the people speaking about it typically seem to use language that says something did exist and something did happen, rather than saying that they are thinking that their concept might explain what we see - after some more research to work out the problems.Reply
So, not really very convincing to a person with a lot of STEM background but no substantial expertise in the theories that these theorists seem to accept as fact.
The main gist of this video is that the universe we have now started with a "field" that was in all space (wherever that was) with a lot of potential energy associated with it. That field then expands by a factor of 10^27, so anything already in the field becomes so stretched that it doesn't really have any further impact on the universe. But, the stretched field, which no longer exists at all today, breaks into multiple other coupled fields that convey charge, mass, etc. and those fields have mathematical local vibration solutions that are effectively fragments of the stretched fields that become the particles that we (think) we understand today.
My reaction is just to think "Maybe, but maybe not."
This video has a "hot big bang" that occurs "after inflation", so inflation is no longer the "big bang", and that is getting confusing for anybody who listens to different speakers with different ideas at different times.
With all of the variations in ideas of how the early universe was created and evolved, I expect that there will be some theorist who will claim that any new discovery of gravitational wave forms fit his/her particular ideas, and claim that indicates that their ideas are correct.
But. that is not convincing logic. What would be needed to convince me is a showing that there are really no other explanations for the new findings, other than the theory they are alleged to support. I do understand that you cannot logically prove a negative conjecture in absolute terms. But, I would want to see an honest search for other explanations and a convincing argument that those other explanations are not true. The logic I am seeing today just seems to have too much confirmation bias and not enough reality checking. -
Torbjorn Larsson
The video was just intended as context to slow roll inflation, a concept that like reheating has been around since the 70's and like it has been increasingly supported by evidence. The scientist group's current research on "parametric resonance" reheating was not intended as part of that larger context.Unclear Engineer said:After watching the video, it seems that the thinking and the terminology keep changing, and are not actually a generalized consensus among just about all researchers. ... The logic I am seeing today just seems to have too much confirmation bias and not enough reality checking.
Speaking of context, it is no one's particular fault that different researchers may define "big bang" differently, it's just how it is and we have to live with it.
(Note that the image is 10 years old, from about the time that the Planck observatory observed inflation for the first time. https://profmattstrassler.com/2014/03/26/which-parts-of-the-big-bang-theory-are-reliable/)
It is a fact that inflation, and specifically the scalar field version of slow roll, are still open questions despite that inflation is part of the new "concordance cosmology" and, as the quote below claims "The basic inflationary paradigm is accepted by most physicists." Dark energy-dark matter (LCDM) theory of the hot big bang has plenty of observational evidence but only 5 testable parameters of which all have been tested. Inflation has less evidence, mostly from statistics of cosmic filaments (since the field fluctuation seeded them) and of cosmic background radiation (since the tensor background from primordial gravitational waves are yet to be observed), so only 4 out of 6 potential tests have been made.
The discovery of a Higgs scalar field and the BICEP/Keck observations of the tensor-to-scalar ratio of cosmic background radiation has made slow roll inflation the most promising inflation theory.
It explains the origin of the large-scale structure of the cosmos. Quantum fluctuations in the microscopic inflationary region, magnified to cosmic size, become the seeds for the growth of structure in the Universe (see galaxy formation and evolution and structure formation). Many physicists also believe that inflation explains why the universe appears to be the same in all directions (isotropic), why the cosmic microwave background radiation is distributed evenly, why the universe is flat, and why no magnetic monopoles have been observed.
https://en.wikipedia.org/wiki/Cosmic_inflation
The detailed particle physics mechanism responsible for inflation is unknown. The basic inflationary paradigm is accepted by most physicists, as a number of inflation model predictions have been confirmed by observation; however, a substantial minority of scientists dissent from this position. The hypothetical field thought to be responsible for inflation is called the inflaton.
In the image below of the by now fairly old BICEP/Keck observations of the cosmic background fluctuations, the observed lower values of the tensor-to-scalar ratio is suggestive of a simple inflaton scalar field. (The green area is a non-relativistic hypothesis, the rejected blue are are the simplest non-scalar inflaton fields.)
Figure 2: This schematic shows the new constraints from BICEP/Keck (red) on r, the tensor-to-scalar ratio, and n_s, the scale dependence of the density fluctuations. Also shown are the predictions from certain inflation models: monomial or power-law models (blue) and Starobinsky-inspired models (green). Other inflation models (not shown) predict lower values of r. The horizontal lines depict the expected sensitivities of future experiments: the Simons Observatory (yellow) and the CMB-S4 experiment (light blue).
https://physics.aps.org/articles/v14/135 -
Unclear Engineer No disrespect intended, but my experiences with modelers in other fields is that they tend to believe their models, even the ones that turn out to be incorrect with later information.Reply
At this point in my understanding of physics and math, it seems to me that the cosmology modelers and the subatomic physics modelers are taking great liberties with the uses of "fields" that they really cannot define in terms that most people recognize as real.
We do seem to find wavelike behaviors, but we really do not understand how waves could propagate in "nothing". So, "fields" are the "something" that theorists provide for the waves to propagate in. But, then, the things that we think exist physically are theorized to be only waves in these fields. That really turns the concept in its head, compared to what engineers would call a "field" - which is a set of measured influences distributed in space due to something that is defined as their cause, such as a positive charge on a metal ball creating a spatial distribution of voltage potentials that can be measured. But, the physicists claim that there is always a field, everywhere, and something with a charge on it is itself only a perturbation in the field - and other types of fields that are "coupled".
This seems like a regression from the realization that light waves do not propagate through an "ether" that we can measure our velocity through. Yes, Special Relativity Theory effectively mathematically models changes in measured lengths and time intervals that prevent any measurement of a velocity through an "ether", if one exists. So, a "field" can be such a medium for wave propagation. But it is a concept, not a measure entity.
So, when you say that the Higgs Field was "discovered", I take that to mean when it was conceptualized. Making a model fit something is not really a proof that the model is correct if there are unconstrained parameters in the model that can be arbitrarily modified to make it fit observations. I do see that there are efforts to deduce constraints.
But, the whole theory development process seems to be focused on trying to backwards extrapolate the observation, that the universe is expanding, back to the time when it would all have been in a single point. Considering how little we really can observe past 13 billion years ago, it seems like there should also be some effort put into thinking about what the possibilities are for that extrapolation to become unrealistic well before the time when the whole universe was smaller than an atom.
If we can accept theories about a process called "inflation" that we cannot explain other than it provides a concept that makes an otherwise unworkable model seem to work, I think we could dream-up other unexplainable processes that would result in all sorts of cyclic behaviors of our universe, if that was the goal instead of creating a model that fits the concept of starting from a single point. -
Classical Motion Insert a precision fully rectified sine-wave into the feedpoint of an antenna. Then you will start to understand a “wave”. They are not waves. They are field packets. Almost perfectly spherical packets and they expand as the propagate. That sphere is referenced to the incidence of emission. A one direction sphere. Think of an expanding equator instead of an expanding sphere or ball. The little photon grows and expands to the largest structures in this universe. At a rate of 2 times c. That growth dissolves the packet into the background static. Only great fluxes of aligned photons can be seen at great distances thru space. A spherical ball of emitters will emit spherical flux. But the little photon is an expanding doughnut field. But the flux of many is spherical.Reply
All those photon expansions are referenced back to a single point in space. Only a photon can have a single point location reference in space. No matter the age of the light. One point.
EM emission is an instant act. And because it is, the velocity of the emitter does not add to the velocity of the propagation. All light has the some velocity. Because it was emitted instantly. That’s a big deal and an important concept.
But light takes time to be absorbed or detected. Or I should say mass takes time to absorb or detect it. Because mass has inertia. AND therefore the interaction time of light with mass depends on the mass velocity. JUST like all other velocities interact.
Detector motion distorts the normal interaction time. That changes the time of mass motion. And that mass motion is the so called frequency of light.
ONLY the DISTANCE(not time) between packets changes with emitter motion. This is called an inverted duty cycle. And this is the part of the shift with emitter motion. This added distance will change the off time of the duty cycle. …. when it is detected. Do you see that?
The other part of the shift is detector motion. TWO independent shifts. This is important, very important.
Light is not a line it is a blink. It’s sequential discreet field durations. With no motion, 50% duty cycle. And with emitter motion, only the off time is varied. With detector motion, both on and off times are varied the same amount.
Try it.
The extra spacetime(off-time) from emitter motion…. is carried…..clear across this universe.
Space is square. -
Torbjorn Larsson Unclear Engineer said:No disrespect intended, but my experiences with modelers ...
If we can accept theories about a process called "inflation" that we cannot explain other than it provides a concept ...
Before I return to the OP question of the order of the inflationary phase transition, I want to point out - as I have described - inflation theory as based on its observed predictions is part of the concordance cosmology (inflation era, followed by hot big bang era). "The basic inflationary paradigm is accepted by most physicists."Here'smythought said:It comes down to what is real, and how that can be shown to be real.
Slow roll inflation is arguably also not a model any longer, as the BICEP/Keck observations show, the tensor-to-scalar ratio is too low. The significance is shy of 3 sigma as of yet, but what alternative do we have when the ratio goes down at each new observation!?
As for quantum field theory, it is non-arguably the most basic physics we have. What remains as examples of models would be the exact slow roll field mechanism.
Which brings us back to the order of the phase transition. Since slow roll is what we appear to see, the second order phase transition follows and not the first order, rapid bubble and strong primordial gravitational wave forming with latent heat as was first suggested here. (The inflation energy released in the slow roll second order phase transition is described by the oscillations around the ground state in the video, if such details interest. That part is independent of the field model.) It seems to be consensus, despite that I personally thought it was first order until last year or so -bubble formation and latent heat is a handy model - when I got wiser on how the second order phase transition works here.
What you describe are not wave or field packets. Quantum field theory describes a photon distribution at emission, not single photons, and they travel with the universal speed limit c in vacuum.Classical Motion said:Insert a precision fully rectified sine-wave into the feedpoint of an antenna. Then you will start to understand a “wave”. They are not waves. They are field packets. Almost perfectly spherical packets and they expand as the propagate. That sphere is referenced to the incidence of emission. A one direction sphere. Think of an expanding equator instead of an expanding sphere or ball. The little photon grows and expands to the largest structures in this universe. At a rate of 2 times c.
There are a bunch of other erroneous or unknown claims in the comment, so I just pulled an example here. -
jrvillalba
If... the Universe started as a self-contained entity/isolated system, as the onset of existences under parameters of Physical Nature (the Singularity), perhaps its extreme heat and extreme density conveyed such a state of extreme high pressure, very much capable of bringing forth its own unfathomable explosion (the Big Bang). First blast wave: supersonic outward dissemination of its parts (matter-mass/energy/charge (pushing effect/CMBR); followed by second blast of negative pressure sucking parts back into its center (pulling effect/UGC). Where, the source of these low-frequency nanohertz gravitational waves could be the remnants of the 2nd blast wave of the Big Bang explosion. As such, their uniform permanence in the cosmos could have been conveyed along the onset of ordinary matter/dual M-E entities, as open systems capable of generating their own heat/radiation and density/gravitation. Or... the Universe as an isolated system sustaining the existence of many open systems.Admin said:If the gravitational wave background detected last year came from a "supercool" phase transition around the time of the Big Bang, they hint at new physics.
Gravitational waves hint at a 'supercool' secret about the Big Bang : Read more