Quantum equations suggest the big bang never happened

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http://www.iflscience.com/physics/quantum-equations-dispute-big-bang

Two physicists are trying to revive one of the great debates of twentieth-century science, arguing that the Big Bang may never have happened. Their work presents a radically different vision of the universe from the one cosmologists now work with.
Should we be taking this seriously or not? Thoughts?
 

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  • #2
phinds
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  • #3
Chalnoth
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I.e., no, there's no reason to take this seriously.

It's standard knowledge within cosmology that the big bang singularity is impossible. The question remains as to what was going on in the densest times. There are two general approaches that theorists have taken in an attempt to explain the discrepancy:
1. Come up with an alternative model which, when extrapolated forward in time, gives a universe that looks like our own. Cosmic Inflation is one example of following this paradigm.
2. Take the currently-known components of our universe and extrapolate backward in time towards the singularity, but make use of a theory of quantum gravity to describe the universe at very early times. Loop Quantum Cosmology is one example here. This is also the approach taken by Ali and Das.

Personally, I tend to favor the first approach, but we don't yet have evidence to show which approach is more likely to produce results, or which specific theory is likely to be accurate.
 
  • #6
TeethWhitener
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Anywhere you see " ... overwhelmingly favor the idea that the universe came into being from a single, infinitely dense point." run, don't walk, away.
I.e., no, there's no reason to take this seriously.
The actual paper was just published in Phys. Lett. B (decently reputable journal). Here's the arxiv: http://arxiv.org/abs/1404.3093v3
The paper itself is interesting, although it's not an area I know much about. It basically takes the Raychaudhuri equation and replaces the geodesics with Bohmian trajectories (from Bohm's quantum analogue of the Hamilton-Jacobi equation). This guy Das has another paper in Phys. Rev. D explaining this procedure, but again, not my area of expertise, so I'm not sure how well I can speak to the veracity of it. But long story short, it turns out when you do a few substitutions on this quantum Raychaudhuri equation, you get the Friedmann equations with a few extra terms, one of which looks like a cosmological constant and another of which eliminates the big bang singularity. It might be speculative, but it isn't worth writing off without a second look.
 
  • #7
Chalnoth
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The actual paper was just published in Phys. Lett. B (decently reputable journal). Here's the arxiv: http://arxiv.org/abs/1404.3093v3
The paper itself is interesting, although it's not an area I know much about. It basically takes the Raychaudhuri equation and replaces the geodesics with Bohmian trajectories (from Bohm's quantum analogue of the Hamilton-Jacobi equation). This guy Das has another paper in Phys. Rev. D explaining this procedure, but again, not my area of expertise, so I'm not sure how well I can speak to the veracity of it. But long story short, it turns out when you do a few substitutions on this quantum Raychaudhuri equation, you get the Friedmann equations with a few extra terms, one of which looks like a cosmological constant and another of which eliminates the big bang singularity. It might be speculative, but it isn't worth writing off without a second look.
Yes, just to be clear: the work itself is potentially interesting, if you like speculative theories (I haven't looked at it in detail). I was merely talking about the news article, which is sensationalist and misleading.
 
  • #8
phinds
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Yes, just to be clear: the work itself is potentially interesting, if you like speculative theories (I haven't looked at it in detail). I was merely talking about the news article, which is sensationalist and misleading.
Yeah, me too.
 
  • #9
bapowell
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1. Come up with an alternative model which, when extrapolated forward in time, gives a universe that looks like our own. Cosmic Inflation is one example of following this paradigm.

Personally, I tend to favor the first approach, but we don't yet have evidence to show which approach is more likely to produce results, or which specific theory is likely to be accurate.
Except that the inflationary universe still must contend with the initial singularity.
 
  • #10
Chalnoth
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Except that the inflationary universe still must contend with the initial singularity.
It is true that cosmic inflation doesn't eliminate the singularity, it just pushes it further back in time (by an indeterminate amount), in that if you extrapolate the inflationary universe back in time you get a singularity eventually. But my statement was about the general paradigm of thinking of how to solve the problem of the singularity, and you can just apply the same paradigm again to cosmic inflation. Some examples of ideas based in cosmic inflation that avoid an initial singularity include considering a quantum vacuum fluctuation from an empty universe with a small but positive cosmological constant, or considering a tunneling event from a previous false vacuum state. Either of these allow an inflationary universe to begin without an initial singularity.
 
  • #11
A DeSitter zero entropy quantum vacuum ?
 
  • #12
Chalnoth
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A DeSitter zero entropy quantum vacuum ?
I do not know what you're asking, but DeSitter space does not have zero entropy: it has entropy proportional to the area of the cosmological horizon.
 
  • #13
I do not know what you're asking, but DeSitter space does not have zero entropy: it has entropy proportional to the area of the cosmological horizon.
Didn't the Cassimir Experiment suggest such a possibility ? The Universe "popped up " from nothing , and that nothing being the DeSitter model ? And that , based on Quantum Theory ?
 
  • #14
Ken G
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It's up to scientists to change the question into the one science really deals with. Science does not deal with the question "did the Big Bang happen", because the Big Bang was not an event, it is an evolutionary story that starts from a position of significant certainty located in our present time and vicinity, and describes backward in time, involving more and more phenomena, toward more and more uncertainty, as the observations get more difficult (or impossible), and the theories get more speculative. I'm sorry if the general public cannot think in terms of that kind of nuance, but it is still our duty as those who can to make sure the question does not get turned into something pseudoscientific.
 
  • #15
PeterDonis
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Didn't the Cassimir Experiment suggest such a possibility ?
The Casimir effect shows that quantum vacuum fluctuations in a field can have real physical effects; but the field in that experiment is the electromagnetic field, which has a vacuum expectation value of zero. The de Sitter universe and the inflationary model require a field (either a cosmological constant or a scalar field) with a nonzero vacuum expectation value, which is a different thing.
 
  • #16
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Let me clarify my question. They claim to solve the coincidence problem, what do they exactly mean by that, and How did they do that.
Perhaps I'm wrong, but it looked to me like they "solved" it with pure sleight of hand-- they embedded the current size of our observable universe as if it was a "natural" parameter in their theory, and then the fact that dark energy is just starting to dominate seems "natural" as well, but it's actually still a coincidence. Their main point seemed to be that the term corresponding to a cosmological constant falls out naturally, but it's perhaps not too shocking that a constant term can appear in a quantum "correction."
Can somebody elaborate please.So, are they saying that the matter energy in the universe equals vacuum energy.
 
  • #17
It's up to scientists to change the question into the one science really deals with. Science does not deal with the question "did the Big Bang happen", because the Big Bang was not an event, it is an evolutionary story that starts from a position of significant certainty located in our present time and vicinity, and describes backward in time, involving more and more phenomena, toward more and more uncertainty, as the observations get more difficult (or impossible), and the theories get more speculative. I'm sorry if the general public cannot think in terms of that kind of nuance, but it is still our duty as those who can to make sure the question does not get turned into something pseudoscientific.
What is "un-scientific " about proposing the Big Bang never happened ? And what is this "position of significant certainty " ? In the Standard Model the only thing that can be said with certainty can only trace back to a point AFTER the initial event . As far as using the term pseudoscientific , this idea by these two scientists can not be thought of as such , after all, Hoyle 's Steady State was never termed pseudo-scientific , was it ? Yes it has been put to rest , but I'm sure Hoyle's getting a chuckle right now .
 
  • #18
The Casimir effect shows that quantum vacuum fluctuations in a field can have real physical effects; but the field in that experiment is the electromagnetic field, which has a vacuum expectation value of zero. The de Sitter universe and the inflationary model require a field (either a cosmological constant or a scalar field) with a nonzero vacuum expectation value, which is a different thing.
Correct me if I am in error , but wasn't the results [ although debatable ] of that experiment used by quantum theorists to hypothesize a possibility of how the Universe initially started it's inflation ?
 
  • #19
PeterDonis
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wasn't the results [ although debatable ] of that experiment used by quantum theorists to hypothesize a possibility of how the Universe initially started it's inflation ?
Not to my knowledge. Again, the kind of vacuum fluctuations involved in hypotheses about how inflation got started are not the same as the kind of vacuum fluctuations whose effects were detected in the Casimir effect experiment. I suppose you could view the experiment as giving support for the general idea of vacuum fluctuations, but nobody to my knowledge has cited the experiment as a contributing factor in the models about how inflation started.

Also, why do you say the results of the Casimir effect experiment are "debatable"?
 
  • #20
Ken G
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What is "un-scientific " about proposing the Big Bang never happened ?
To answer that, you have to say what you mean by that it did happen, or that it did not happen, and make either a scientific statement. Be completely specific about what you mean by the words.
And what is this "position of significant certainty " ?
That which we observe, like the Earth, the nearby stars, the Hubble law in near the local group of galaxies. Those are all things of significant certainty in astronomy. Going further, and back in time, the uncertainties grow, we have event horizons, dark matter, dark energy, inflation, the Planck scale, etc.
In the Standard Model the only thing that can be said with certainty can only trace back to a point AFTER the initial event .
What initial event are you talking about? What testable and objectively verifiable scientific model includes such a thing, or rules out such a thing?
As far as using the term pseudoscientific , this idea by these two scientists can not be thought of as such , after all, Hoyle 's Steady State was never termed pseudo-scientific , was it ?
Even if you have a steady-state model, and you demonstrate that it agrees with all observations, it is pure pseudoscience to extend that model to a time of negative infinity. It simply isn't what you can use a model to do, and still be doing science.
Yes it has been put to rest , but I'm sure Hoyle's getting a chuckle right now .
Yet that's just what I'm talking about-- if one does not think scientifically about what the purpose of a model is, then one takes a very black-or-white view of what a model is doing. So either the universe began in some singularity, or else it existed forever, and either of those possibilities makes perfect sense, regardless of whether or not we have any means of making any observations that could ever rule either one out. What's more, if we find evidence that some set of equations seems to resonate better with our current prejudices, this means Hoyle was right after all. The idea of universal inflation has been around for much longer than these "quantum corrections", and universal inflation has an infinitely old universe also, in something much closer to a steady-state model.
 
  • #21
Not to my knowledge. Again, the kind of vacuum fluctuations involved in hypotheses about how inflation got started are not the same as the kind of vacuum fluctuations whose effects were detected in the Casimir effect experiment. I suppose you could view the experiment as giving support for the general idea of vacuum fluctuations, but nobody to my knowledge has cited the experiment as a contributing factor in the models about how inflation started.

Also, why do you say the results of the Casimir effect experiment are "debatable"?
There was some dispute as to the particles allegedly found, had already existed and were not produced by the experiment , but simply were not detected .
Not to my knowledge. Again, the kind of vacuum fluctuations involved in hypotheses about how inflation got started are not the same as the kind of vacuum fluctuations whose effects were detected in the Casimir effect experiment. I suppose you could view the experiment as giving support for the general idea of vacuum fluctuations, but nobody to my knowledge has cited the experiment as a contributing factor in the models about how inflation started.

Also, why do you say the results of the Casimir effect experiment are "debatable"?
The finding a raises a physical problem: there's nothing to stop arbitrarily small waves from fitting between two mirrors, and there is an infinite number of these wavelengths. The mathematical solution is to temporarily do the calculation for a finite number of waves for two different separations of the mirrors, find the associated difference in vacuum energies and then argue that the difference remains finite as one allows the number of wavelengths to go to infinity.

Although this trick works, and gives answers in agreement with experiment, the problem of an infinite vacuum energy is a serious one. Einstein's theory of gravitation implies that this energy must produce an infinite gravitational curvature of spacetime--something we most definitely do not observe. The resolution of this problem is still an open research question.

Ergo nihilo ex nihilo . Otherwise put no quantum fluctuations from nothing ,and the experiment really did not prove that there was in fact absolute empty space between the mirrors to start with .
 
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  • #22
PeterDonis
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The finding a raises a physical problem
I would say it raises a theoretical problem. The experimental result is what it is. See below.

the problem of an infinite vacuum energy is a serious one. Einstein's theory of gravitation implies that this energy must produce an infinite gravitational curvature of spacetime--something we most definitely do not observe. The resolution of this problem is still an open research question.
Yes, but it's a problem of what theory to use, not what the actual vacuum energy is. The actual energy of the vacuum is very, very small; we know that because, as you say, the curvature of spacetime produced by it is very small (so small that we can only observe it indirectly, by its effects on the dynamics of the universe as a whole). The problem is how to account for this theoretically; none of our current theories predict the vacuum energy we actually observe. They either predict that it should be infinite (the standard quantum field theory prediction when you sum over an infinite number of modes) or zero (if you do the trick of subtracting off the infinite sum). (Note that this is for the case where there are no metal plates or anything else present to perturb the vacuum; as you say, for the case where we perturb the vacuum slightly, as in the Casimir effect, we can do the trick of subtracting off the infinite vacuum sum to get the right prediction, but that doesn't resolve the issue of how to account for the unperturbed case.)

Ergo nihilo ex nihilo . Otherwise put no quantum fluctuations from nothing ,and the experiment really did not prove that there was in fact absolute empty space between the mirrors to start with .
I don't understand what this means.
 
  • #23
PeterDonis
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There was some dispute as to the particles allegedly found, had already existed and were not produced by the experiment , but simply were not detected .
Huh? The actual measurement doesn't detect the virtual particles (you can't detect virtual particles directly, by definition); it detects the force between the plates. The virtual particles are part of the theory we use to account for why the force is there (standard classical electrodynamics says there should be zero force between uncharged plates). The experimental result (the presence of the force) has been confirmed multiple times and is not in any doubt. The theory is another matter (see my previous post).
 
  • #24
To answer that, you have to say what you mean by that it did happen, or that it did not happen, and make either a scientific statement. Be completely specific about what you mean by the words.
That which we observe, like the Earth, the nearby stars, the Hubble law in near the local group of galaxies. Those are all things of significant certainty in astronomy. Going further, and back in time, the uncertainties grow, we have event horizons, dark matter, dark energy, inflation, the Planck scale, etc. What initial event are you talking about? What testable and objectively verifiable scientific model includes such a thing, or rules out such a thing?
Even if you have a steady-state model, and you demonstrate that it agrees with all observations, it is pure pseudoscience to extend that model to a time of negative infinity. It simply isn't what you can use a model to do, and still be doing science.Yet that's just what I'm talking about-- if one does not think scientifically about what the purpose of a model is, then one takes a very black-or-white view of what a model is doing. So either the universe began in some singularity, or else it existed forever, and either of those possibilities makes perfect sense, regardless of whether or not we have any means of making any observations that could ever rule either one out. What's more, if we find evidence that some set of equations seems to resonate better with our current prejudices, this means Hoyle was right after all. The idea of universal inflation has been around for much longer than these "quantum corrections", and universal inflation has an infinitely old universe also, in something much closer to a steady-state model.
The initial event I refer to is the start of the inflation . Which to my knowledge remains inscrutable [ at the moment ] .I found it just a bit ironic that these two scientists with their calculations are hinting at just that , or is their reference to an infinitely old Universe , otherwise put, a Universe existing forever , not unlike Hoyle's Steady State model ? When you ask "what testable and objectively verifiable scientific model includes such a thing ..." are you being rhetorical , as that statement is more or less a given , since we have no empirical evidence , no testability , nor any equation that can be used beyond 3 planck segments of time after the [choose A or B } Big Bang / Super Inflation .
 
  • #25
Huh? The actual measurement doesn't detect the virtual particles (you can't detect virtual particles directly, by definition); it detects the force between the plates. The virtual particles are part of the theory we use to account for why the force is there (standard classical electrodynamics says there should be zero force between uncharged plates). The experimental result (the presence of the force) has been confirmed multiple times and is not in any doubt. The theory is another matter (see my previous post).
The measurement of particles is by their electrical charge is it not ? Those detected in the Cassimir experiment were questioned by other scientists and the experiment deemd inconclusive , since all wavelengths were not measured , so that there was no assurance that those wavelengths had not already been existing . And yes I agree the theory is another matter .
 

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