Quantum equations suggest the big bang never happened

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Two physicists are challenging the Big Bang theory, suggesting it may never have occurred, which has sparked debate in the scientific community. Their approach utilizes quantum equations to propose an alternative model that eliminates the singularity associated with the Big Bang. While some participants in the discussion express skepticism about the validity of this claim, others argue that the work merits further examination despite its speculative nature. The conversation also touches on the limitations of current cosmological models and the complexities of understanding the universe's origins. Overall, the debate highlights the ongoing exploration of cosmological theories and the need for rigorous scientific scrutiny.
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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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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.
 
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phinds said:
Anywhere you see " ... overwhelmingly favor the idea that the universe came into being from a single, infinitely dense point." run, don't walk, away.
Chalnoth said:
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.
 
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TeethWhitener said:
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.
 
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Chalnoth said:
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.
 
Chalnoth said:
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
bapowell said:
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
magneticnorth said:
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
Chalnoth said:
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
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.
 
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  • #15
magneticnorth said:
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
ftr said:
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.

Ken G said:
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
Ken G said:
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
PeterDonis said:
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
magneticnorth said:
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
magneticnorth said:
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
PeterDonis said:
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 .
PeterDonis said:
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
magneticnorth said:
The finding a raises a physical problem

I would say it raises a theoretical problem. The experimental result is what it is. See below.

magneticnorth said:
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.)

magneticnorth said:
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
magneticnorth said:
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
Ken G said:
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
PeterDonis said:
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 .
 
  • #26
I would drop the Casimir side point. One can calculate the Casimir force without regard to a vacuum at all. Therefore it cannot possibly tell you properties of the vacuum. It can only add confuision.
 
  • #27
Vanadium 50 said:
I would drop the Casimir side point. One can calculate the Casimir force without regard to a vacuum at all. Therefore it cannot possibly tell you properties of the vacuum. It can only add confuision.
Some theoretical quantum mathematicians implied that it is from such a vacuum , that is one, devoid of matter space and time , that by quantum fluctuations the Universe popped into existence and inflation began . They used the results of the cassimir experiment as a possibility for this .
 
  • #28
magneticnorth said:
The initial event I refer to is the start of the inflation .
So when you said "the Big Bang never happened", what you really meant was, "inflation never happened". There's a pretty big difference there-- for example, it would be perfectly normal to teach the Big Bang as a story of the history of the universe to introductory students, without mentioning inflation at all. Also, inflation was not the part of the story Hoyle wished to replace with his steady-state model-- indeed, as I said, eternal inflation acts a lot like Hoyle's model, yet that is what Das and company are rejecting. So their result is a lot less like Hoyle's model than is many of the alternatives that involve inflation.
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 .
Which was my point in stressing the crucial differences between "the Big Bang" and various models with or without inflation.
 
  • #29
PeterDonis said:
I would say it raises a theoretical problem. The experimental result is what it is. See below.
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.)
I don't understand what this means.
Nothing comes from nothing , something can not come from nothing - as it relates to Inflation arising from a DeSitter quantum vacuum . The Cassimir effect was used by some to hypothesize the inflation as possibly coming from such .
 
  • #30
Ken G said:
So when you said "the Big Bang never happened", what you really meant was, "inflation never happened". There's a pretty big difference there-- for example, it would be perfectly normal to teach the Big Bang as a story of the history of the universe to introductory students, without mentioning inflation at all. Also, inflation was not the part of the story Hoyle wished to replace with his steady-state model-- indeed, as I said, eternal inflation acts a lot like Hoyle's model, yet that is what Das and company are rejecting. So their result is a lot less like Hoyle's model than is many of the alternatives that involve inflation.Which was my point in stressing the crucial differences between "the Big Bang" and various models with or without inflation.
Hoyle's model was rejected with the discovery of the red shifted light spectrum of objects observed , indicating a velocity away from us . Hoyle basically argued that the redshift was being misinterpreted . Hence Hoyle was arguing that the Universe was perpetual . This is similar in part to what Das is indicating . I didn't say I subscribed to it , just noted an irony ,since what they are saying resembles more closely in one respect, to what Hoyle was arguing . Big Bang from a exploding singularity , or Super Inflation starting at some point before 3 Planck segments of time is in fact irrelevant as they relate to Hoyle's model since he believed neither . I just found it curious that Hoyle , in view of those discoveries , still held to the Steady State model .Das and company stated that their math did not indicate a Universe that would inflate then fall in upon itself and repeat .
 
  • #31
magneticnorth said:
Hoyle's model was rejected with the discovery of the red shifted light spectrum of objects observed , indicating a velocity away from us . Hoyle basically argued that the redshift was being misinterpreted . Hence Hoyle was arguing that the Universe was perpetual . This is similar in part to what Das is indicating .
Yes but eternal inflation also says that the universe is eternal, and what's more, it is in a steady state overall-- much more like Hoyle's idea. So the Big Bang, plus eternal inflation, is actually very close to steady-state cosmology (not static cosmology, note). Putting in quantum corrections that eliminate eternal inflation thus takes the whole picture very far away from steady-state cosmology, I don't think Hoyle would have liked it, though he would have liked the absence of an origin.

I didn't say I subscribed to it , just noted an irony ,since what they are saying resembles more closely in one respect, to what Hoyle was arguing .
I realize you are not arguing in favor of the model, nor I against it, I'm merely pointing out that nothing has really changed because we have no new observations, and no more reason to believe in or reject inflation. Also, the Das model is farther from Hoyle's cosmology.
I just found it curious that Hoyle , in view of those discoveries , still held to the Steady State model .
I think Hoyle ended up with a view that was a lot like eternal inflation. His view was always consistent with cosmological redshifts, but not with changing populations in the universe, like quasars. But when it was clear quasars did exist, Hoyle just modified his views to allow some secular evolution, but still an ongoing creation process that preserves a steady state overall. That's pretty much exactly what eternal inflation is, but there would be no need to invoke eternal inflation with the Das approach.
 
  • #32
Ken G said:
Yes but eternal inflation also says that the universe is eternal, and what's more, it is in a steady state overall-- much more like Hoyle's idea. So the Big Bang, plus eternal inflation, is actually very close to steady-state cosmology (not static cosmology, note). Putting in quantum corrections that eliminate eternal inflation thus takes the whole picture very far away from steady-state cosmology, I don't think Hoyle would have liked it, though he would have liked the absence of an origin.

I realize you are not arguing in favor of the model, nor I against it, I'm merely pointing out that nothing has really changed because we have no new observations, and no more reason to believe in or reject inflation. Also, the Das model is farther from Hoyle's cosmology.
I think Hoyle ended up with a view that was a lot like eternal inflation. His view was always consistent with cosmological redshifts, but not with changing populations in the universe, like quasars. But when it was clear quasars did exist, Hoyle just modified his views to allow some secular evolution, but still an ongoing creation process that preserves a steady state overall. That's pretty much exactly what eternal inflation is, but there would be no need to invoke eternal inflation with the Das approach.
Thank you for that explanation Ken G . I would agree , especially with the discovery of quasars , which in Hoyle's Steady State would be contradictory . I think it important to learn what they are , because it is curious that galaxies at 13 billion light years look the same , one would think, looking back that far in time and expect to observe an evolution/ formation of galaxies .
 
  • #33
magneticnorth said:
The measurement of particles is by their electrical charge is it not ?

That's one way of measuring particles that have charge, yes. But it has nothing to do with what was being measured in the Casimir effect experiment. The plates were uncharged. The virtual particles in question (in the usual QFT model of the experiment) are virtual photons, not virtual electrons. Photons have no charge.

magneticnorth said:
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 .

Do you have a reference for any of this? It doesn't match what I know of the experiment at all.
 
  • #34
magneticnorth said:
Some theoretical quantum mathematicians implied that it is from such a vacuum , that is one, devoid of matter space and time , that by quantum fluctuations the Universe popped into existence and inflation began . They used the results of the cassimir experiment as a possibility for this .

Do you have a reference for the last statement? I'm not aware of anyone citing the Casimir effect in any theoretical discussion about the quantum fluctuation hypothesis for the origin of the universe.
 
  • #35
magneticnorth said:
Nothing comes from nothing , something can not come from nothing - as it relates to Inflation arising from a DeSitter quantum vacuum .

Are you saying you don't think this model of inflation is valid? If not, why not? Do you have a reference for such an argument?

magneticnorth said:
The Cassimir effect was used by some to hypothesize the inflation as possibly coming from such .

Again, do you have a reference?
 
  • #36
Ken G said:
the Big Bang, plus eternal inflation, is actually very close to steady-state cosmology (not static cosmology, note).

I don't think so, except in the trivial sense that the universe is eternal in both cosmologies. The steady-state cosmology involves a very different detailed description of the dynamics of the universe, compared to Big Bang + eternal inflation.
 
  • #37
PeterDonis said:
Do you have a reference for the last statement? I'm not aware of anyone citing the Casimir effect in any theoretical discussion about the quantum fluctuation hypothesis for the origin of the universe.
Yes , it is an article from Scientific American http://www.scientificamerican.com/article/what-is-the-casimir-effec/ If I have misinterpreted this , please specify .
 
  • #38
magneticnorth said:

I don't see anything here about the universe originating in a quantum fluctuation; it's just a discussion of the Casimir effect and the issue with the vacuum energy calculation. Also, there's nothing here about particles being detected; the experiments just measure the attractive force between the "mirrors".

(I also don't like the use of the word "mirrors" in the article; the Casimir effect is not limited to mirrors. I've been dissatisfied with Scientific American for some time now because of things like this; I'm not sure if it's the scientists taking liberties because it's not a peer-reviewed journal, or the editors just not catching misstatements, but either way it's disturbing.)
 
  • #39
PeterDonis said:
I don't think so, except in the trivial sense that the universe is eternal in both cosmologies. The steady-state cosmology involves a very different detailed description of the dynamics of the universe, compared to Big Bang + eternal inflation.
Different in detail, yes, but the overall spirit of the later versions of the steady-state cosmology is that it could exhibit oscillations that could mimic transitions from deceleration to acceleration, and associated oscillations in matter creation could create the illusion of finite-age universes being created. So you could have periods when matter is injected, followed by periods when the matter injection is turned off, and it all plays out against a secular exponential expansion. So that could sound a lot like eternal inflation, though the details certainly do differ a lot-- the steady state model does not trace back even to a recombination epoch. So I probably should not say "very close to" in terms of the details, only in terms of the overall philosophy of an eternal universe that shows locally transient behaviors that distinguish that place and time from the overall evolution of the universe as a whole, and look like origins of "bubble" universes as Hoyle called them.

The relevance to the Das paper is only that the concept of bubble universes is much more like eternal inflation than like what Das is saying, because Das only needs one of these "bubbles" and still gets that it exists eternally. Of course, if one simply regards a Das universe as a single "bubble" out of many, then again one can return to a picture much like Hoyle's, except for things like the rejection of an epoch of recombination or other such completely different states of the universe. The main distinction in kind between these models, however, is something that is not at all well constrained in any of these theories-- what is the meaning of time when it is not something corresponding to the period when we actually do have observations of the universe.
 
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  • #40
PeterDonis said:
I don't see anything here about the universe originating in a quantum fluctuation; it's just a discussion of the Casimir effect and the issue with the vacuum energy calculation. Also, there's nothing here about particles being detected; the experiments just measure the attractive force between the "mirrors".

(I also don't like the use of the word "mirrors" in the article; the Casimir effect is not limited to mirrors. I've been dissatisfied with Scientific American for some time now because of things like this; I'm not sure if it's the scientists taking liberties because it's not a peer-reviewed journal, or the editors just not catching misstatements, but either way it's disturbing.)
Thank you for that clarification .
 
  • #41
But keep in mind that inflation (which takes over after the Big Bang) is completely based on Quantum Mechanics.
 
  • #42
The characterization of inflation as occurring "after" the Big Bang is a big part of the problem with the whole idea that "the Big Bang never happened." The Big Bang is not the title of an event that originated the universe. Indeed, no such event is ever included in any Big Bang models other than highly speculative ones like brane collisions and such, and no respectable scientist could ever claim that we have incontrovertible evidence that the universe originated in some kind of creation event, nor that it existed forever, nor even that the concept of time we apply in the here and now had any meaning prior to a given stage of our history. Imagining that the "Big Bang" refers to an instant of creation, perhaps in a singular point in space, is an incorrect characterization that dominates popular media. In astrophysics, the Big Bang is a model of the history of the universe that obeys two rules: it is governed by general relativity under an assumption of spatial homogeneity, and its free parameters are fit to match observations throughout the accessible timeline of our universe. As such, the Big Bang model plays out after inflation, not before, although some may include inflation as part of it-- while others who view inflation as more speculative may choose to omit that aspect of the overall Big Bang model. Most educators and textbooks include it in some way, but with significant caveats.

The salient features of the scientifically demonstrated aspects of "the Big Bang" are that the universe has evolved substantially over a period of 13.8 billion years, during which time it went from a vastly high energy density to the situation we find today, passing through stages of nucleosynthesis, recombination, galaxy formation, and stellar nucleosynthesis. When using the language about our cosmological models properly, it is clear that nothing in the Das paper suggests "the Big Bang never happened."
 
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  • #43
Ken G said:
As such, the Big Bang model plays out after inflation, not before, although some may include inflation as part of it--

Can you please clarify this statement in light of this simplification diagram that generally places the "big bang" prior to "inflation"?

1280px-History_of_the_Universe.svg.png


You say that "In astrophysics, the Big Bang is a model of the history of the universe that obeys two rules: it is governed by general relativity under an assumption of spatial homogeneity, and its free parameters are fit to match observations throughout the accessible timeline of our universe." but how does this statement justify placing the big bang after inflation?
 
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  • #44
The picture you are showing, that includes t=0, is just pop science. What "the Big Bang" means in real science can be found in quotes like this: (http://en.wikipedia.org/wiki/Big_Bang)
"The Big Bang theory is the prevailing cosmological model for the earliest known periods of the universe.[1][2][3] It states that the Universe was in a very high density state and then expanded.[4] If the known laws of physics are extrapolated beyond where they are valid there is a singularity."
Note the actual theory is about expansion, and one only gets a singularity if one extrapolates the idea "beyond where it is valid," as pop sci inevitably does. So unfortunately, we see that the term "Big Bang" is used in two completely different ways-- the pop sci meaning of some kind of "creation event", and the way professional scientists use the term in real astronomy applications. In the latter, and in scientifically responsible astronomy education, the term is used to describe an evolutionary model that tells a story of expansion of the universe, whose phases have been well checked against observations, the way science does. But this model also has a strange element, which some regard as its greatest flaw and others as its most exquisite feature-- as time goes backward, the theory leads to a question mark where the laws of physics as we know them break down. This happens prior to reaching a "singularity", so we already know that no model that includes such a singularity could ever be part of a self-consistent description of the universe that is based on well-tested laws of physics.
 
  • #45
He's saying that the placement of the "Big Bang" in the diagram is not covered by the Big Bang model itself, which is mum on the existence of any actual event that originated the universe. The early hot, dense phase that cosmologists identify with the nascent universe occurred after inflation as part of a process called "reheating". It is therefore common for people to refer to the "hot big bang" as occurring after inflation, but by this they don't mean literally the big bang singularity -- just the early hot phase of the universe relevant to observations.
 
  • #46
Perfect, thank you gentlemen for this clarification.
 
  • #47
bapowell said:
He's saying that the placement of the "Big Bang" in the diagram is not covered by the Big Bang model itself, which is mum on the existence of any actual event that originated the universe. The early hot, dense phase that cosmologists identify with the nascent universe occurred after inflation as part of a process called "reheating". It is therefore common for people to refer to the "hot big bang" as occurring after inflation, but by this they don't mean literally the big bang singularity -- just the early hot phase of the universe relevant to observations.
The Big Bang is therefore just a conceptual visualization , for an event that would start the inflation of space time .Time however must be figured in with all postulations regarding inflation .
 
  • #48
magneticnorth said:
The Big Bang is therefore just a conceptual visualization , for an event that would start the inflation of space time .Time however must be figured in with all postulations regarding inflation .
No, I'm saying that the "hot big bang" is identified with the *end* of inflation, known as reheating.
 
  • #49
magneticnorth said:
The Big Bang is therefore just a conceptual visualization , for an event that would start the inflation of space time .Time however must be figured in with all postulations regarding inflation .
That would be the pop-sci meaning of "Big Bang," but scientists already view that meaning as problematical, and prefer to use the term as the label for the well-tested theory of expansion, which bapowell is calling the "hot big bang" model. It's truly unfortunate that this term traces back to a kind of joke by Hoyle, this has allowed the term to be used in highly imprecise ways because it is such a pictorial phrase in the first place. Basically, the model says something very bizarre and unknown must have happened as we extrapolate back toward t=0, but no part of the scientific evidence in favor of the expansion of the universe, often called "the pillars of the Big Bang" (taking the hot big bang model meaning), have anything to do with a creation event. Instead, we have a 13.8 billion year timeline that makes sense. It is significant that the timeline that makes sense against observations is a finite timeline, but "what happened at the t=0 mark" in that timeline is simply not on the timeline, nor is how much longer that timeline could be extended if we ever actually have an observation that motivates us to do so. As of yet, we have no such motivation-- and no such motivation is provided by a speculative theory. The purpose of speculative theories is to motivate new observations, and help interpret them, not to create headlines that only play off on a widespread misunderstanding about the meanings of awkwardly pictorial scientific terms.
 
  • #50
Ken G said:
That would be the pop-sci meaning of "Big Bang," but scientists already view that meaning as problematical, and prefer to use the term as the label for the well-tested theory of expansion, which bapowell is calling the "hot big bang" model. It's truly unfortunate that this term traces back to a kind of joke by Hoyle, this has allowed the term to be used in highly imprecise ways because it is such a pictorial phrase in the first place. Basically, the model says something very bizarre and unknown must have happened as we extrapolate back toward t=0, but no part of the scientific evidence in favor of the expansion of the universe, often called "the pillars of the Big Bang" (taking the hot big bang model meaning), have anything to do with a creation event. Instead, we have a 13.8 billion year timeline that makes sense. It is significant that the timeline that makes sense against observations is a finite timeline, but "what happened at the t=0 mark" in that timeline is simply not on the timeline, nor is how much longer that timeline could be extended if we ever actually have an observation that motivates us to do so. As of yet, we have no such motivation-- and no such motivation is provided by a speculative theory. The purpose of speculative theories is to motivate new observations, and help interpret them, not to create headlines that only play off on a widespread misunderstanding about the meanings of awkwardly pictorial scientific terms.
I agree , nothing is known beyond the point at which we can extrapolate and trace back to . The term itself assumes an explosion in purely visual terms . When an idea like that is presented to the general public , you can not expect anyone to understand or visualize "something very bizarre and unknown " , as the Big Bang has been presented as an explosion , originating from a Singularity . Rightly or wrongly that is the perception , and that is what is depicted in elementary Science books . Only when one looks deeper into the subject , they will quickly realize that no one knows what preceded or caused the inflation , or atleast , that which can be reasonably postulated to date .
 

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