The age of the universe: easy question - hard answer

[SpaceTiger]

At the time Guth first published there were certainly those who "believed" the universe was flat and isotropic, but there was very little real evidence that this was indeed the case. Inflation predicted that the universe should be very flat

Actually, the flatness problem is not just about the flatness of the universe now, but also in the past. The reason is that an omega~1 universe is extremely unstable and if it's within a factor of 100 of flat now, that means that it was very, VERY close to flat at the time of recombination (must fine-tune H_0 to one part in 10^55). In 1980, they knew that the density was within a factor of 100 of the critical density, so there was definitely a problem, as his paper suggests. I suggest you read it for more details.

The Cosmological Principle is a principle, not a theory, and since it is a principle it makes no predictions. Any cosmological theory must obey the Cosmological Principle otherwise it is doomed to failure. The predictions of inflation obey the Cosmological Principle. Isotropy is one prediction of the theory of inflation. Isotropy may also be a prediction of other theories, but that doesn't invalidate the claim that it is predicted by inflation.

Ok, you're right in the sense that isotropy does arise from inflation, but the point I was trying to make was that it's not even close to being a generic prediction of inflation and certainly can't be used to defend its veracity. It's also not true that they didn't know about it at the time, as the horizon problem can be seen from even the crudest observations of the microwave background.

Science proceeds by people advancing hypotheses to explain the facts, and those hypotheses then being (possibly) disproven. No hypothesis can ever be proven to be 100% correct, the best any hypothesis can hope for is to stand the test of time by agreeing with observations and not being proved incorrect. This is where inflation is right now. Its standing up there waiting to be shot down, and so far nobody has offered up any viable contenders or shot it down.

Agreed and I think it has every right to be the preferred theory. I'm just not confident beyond a reasonable doubt, as I said. It simply doesn't have the predictive power of a theory like relativity or Newtonian gravity.

You're misreading me. I never said inflation is a "sure thing"

"No need to invoke coincidences. The explanation is inflation, which drove the universe to almost perfect flatness at the time of the Big Bang..."

I think I can be forgiven for misreading that as certainty.

- what I am saying is its the best candidate we have right now. If you know of a better candidate then I'm sure we would all love to hear about it.

I don't need an alternative to be skeptical. If someone tells you that they saw aliens, do you automatically believe them if you can't immediately come up with another explanation? Besides, in case you didn't know, a large fraction of the astronomical community shares my skepticism. I can understand that you would react this way, as I'll bet you get a lot of crackpots on this message board, but I can assure you that my position on this issue is not fringe.

 

[Garth]

First WMAP has not shown that the universe is flat, only that it is conformally flat, its measurements are angular in nature and conformal transformations preserve angular relationships. When will this glaring fact be recognised?? If the universe were truly flat then there should be no shortage of low l anisotropies in the data. Their deficit exists not only in the WMAP data but also the BALLOON and COBE as well and cannot be ignored as experimental error.

Secondly inflation simply resolves, or fixes a problem of GR cosmology. If the theory did not need to be fixed there would be no reason to invoke inflation.

Thirdly alternatives do exist A Concordant “Freely Coasting” Cosmology, which do not have the problem in the first place. Why is not more significance given to them? Occam's razor would normally guarantee their significance.

Yes, reference comments on my previous post I was using the word 'exact' in an observational and not mathematical sense. And I do consider DM and DE together with inflation to be 'patches' or 'epicycles' invoked to save the standard theory (search for my previous posts on the subject).

Garth

 

[turbo]

... of course Newton was not entirely correct, and he could not explain where gravity "came from", but his ideas and insight advanced science and mechanics for the next 200 years.

Einstein could not explain where gravity "came from" either. He modeled gravitational effects mathematically, and expressed those effects as though masses curve space-time. That approximation works very well (as does the Newtonian approximation) in simple systems, like planets circling a star. It does not work well on galactic and calactic-cluster scales. It cannot model galactic rotation accurately, and does not predict the observed strong cluster lensing or cluster binding. Dark matter (distributed "just so" in each relevant application) is required to fix GR gravity. Instead of inventing dark matter, physicists could have saved a couple of decades, and revisited the curved space-time model of gravitation. That model cannot be reconciled with quantum field theory (which appears to be VERY accurate) - when several conflicts occur with a basic model, especially on such a huge span of scales (nuclear to galactic), we should suspect a problem with the model, and not resort to patches or epicycles.

 

[SpaceTiger]

That model cannot be reconciled with quantum field theory (which appears to be VERY accurate) - when several conflicts occur with a basic model, especially on such a huge span of scales (nuclear to galactic), we should suspect a problem with the model, and not resort to patches or epicycles.

They tried a model that altered gravity at weak accelerations (MOND) and it has performed very poorly. Dark matter is more than just a fix, we have indepedent evidence for it. See, for example:


Clowe et al. 2004

I know dark matter is not an elegant solution to the rotation curve problem, but it works. The discrepancies with QFT at small scales are, more than likely, only relevant at small scales.

 

[turbo]

They tried a model that altered gravity at weak accelerations (MOND) and it has performed very poorly. Dark matter is more than just a fix, we have indepedent evidence for it. See, for example:


Clowe et al. 2004

I know dark matter is not an elegant solution to the rotation curve problem, but it works. The discrepancies with QFT at small scales are, more than likely, only relevant at small scales.

The paper is an interesting and compelling refutation of MOND at cluster scales. The underlying observations are not a confirmation of the existence of dark matter, however. The existence of dark matter is inferred from the failure of GR to properly predict the cluster lensing and cluster member velocities. Further observations of this type cannot be regarded as independent evidence for the existence of dark matter. We know that GR cannot properly predict galactic rotation curves, cluster binding, or cluster lensing, given the luminous matter observed. Some of us are so certain that GR must be right that we are unwilling to challenge it, and so we have to invent entities to "balance the books".

Let's pretend that non-baryonic dark matter does not exist, and we have to observe the universe with the radiation, particles, matter, of the known classical universe. In that case, GR's gravitation model works extremely well on most scales. GR fails to be predictive on galactic scales and larger, however. If we resist the temptation to enshrine GR as "perfect" (and Einstein's made his views on epistemology very well known), we must admit the possibility that GR's gravitational model is flawed - a better approximation perhaps than the Newtonian model, but still not correct.

 

[SpaceTiger]

The paper is an interesting and compelling refutation of MOND at cluster scales. The underlying observations are not a confirmation of the existence of dark matter, however. The existence of dark matter is inferred from the failure of GR to properly predict the cluster lensing and cluster member velocities.

The paper is more than just a refutation of MOND. This is a case of a lensing event separate from the center of light in the cluster. In order to reproduce that in an alternative gravitational model, you'd have to alter the geometry of spacetime (or the non-GR equivalent) asymmetrically from the mass center. Although I'm sure one could concoct a model like that (as one could concoct an arbitrarily complicated one to explain anything), it would have to be extremely ad hoc.

Anyway, you haven't really given a reason for why you think that the author's arguments are wrong, so you'll have to elaborate. Your arguments seem practiced to the more traditional problems of rotation curves and velocity dispersions.

Some of us are so certain that GR must be right that we are unwilling to challenge it, and so we have to invent entities to "balance the books".

Actually, the general feeling of the astronomical community is that we wished we didn't have to invoke dark matter, as its extremely inelegant. However, it has done a far better job of explaining the observations than any alternative model of gravity.

In that case, GR's gravitation model works extremely well on most scales. GR fails to be predictive on galactic scales and larger, however. If we resist the temptation to enshrine GR as "perfect" (and Einstein's made his views on epistemology very well known), we must admit the possibility that GR's gravitational model is flawed - a better approximation perhaps than the Newtonian model, but still not correct.

We know that it's flawed because it's inconsistent with quantum field theory, but alternative models at the scales you're talking about have, so far, all failed. Dark matter is the best fit to observations at this point.

 

[selfAdjoint]

We know that it's flawed because it's inconsistent with quantum field theory, but alternative models at the scales you're talking about have, so far, all failed. Dark matter is the best fit to observations at this point.

AFAIK, QFT can't be well-defined in curved spacetime, any more than GR can be perturbatively quantized. Is that what you mean by saying GR is inconsistent with QFT? Perhaps QFT is inconsistent with GR?

Added: Plus, QFT has consistency problems of its own, see Haag's theorem for example, or Landau pole. Mere accuracy at low orders of perturbation expansion does not a consistent theory make.

 

[turbo]

The paper is more than just a refutation of MOND. This is a case of a lensing event separate from the center of light in the cluster.

That's not what the authors said - emphasis mine:

The detected mass peak is located between the X-ray peak and galaxy concentration, although the position is consistent with the galaxy centroid within the errors of the mass reconstruction.

The authors say that the lensing is consistent with the center of mass center of the clusters, which shows the presence of dark matter in the clusters and refutes the expectation (in MOND) that ram-stripped X-ray gas between the clusters should be expected to exhibit lensing effects.

Anyway, you haven't really given a reason for why you think that the author's arguments are wrong, so you'll have to elaborate. Your arguments seem practiced to the more traditional problems of rotation curves and velocity dispersions.

I am not refuting the lensing effects that they measured, nor the fact that the lensing effects are consistent with the centers of the clusters. I am saying that this is entirely expected, but is not a demonstration of the reality of dark matter. It is instead a measure of the failure of GR to properly predict the strength of gravity in very massive domains. MOND does not perform well in galactic-cluster environments, nor would I expect it to in the model that I have been working on.

We know that it's flawed because it's inconsistent with quantum field theory, but alternative models at the scales you're talking about have, so far, all failed. Dark matter is the best fit to observations at this point.

I have a compelling candidate for dark matter (although it is really more than that). It is almost impossible to detect by any means (save the Casimir Effect), and it suffuses all of space. It's the electromagnetic field of the vacuum - the Zero Point Energy. All we need is a mechanism by which these virtual particle/antiparticle pairs can be polarized. Polarization and densification of the field and the resultant self-attraction will provide the "extra" gravitational attraction in massive domains that perplex GR now. How can these virtual pairs be aligned? By a differential in the gravitational infall rate of matter vs antimatter. The Athena project at CERN is designed to produce experimentally-useful quantities of anti-hydrogen. If my model is correct, the inertial mass of anti-hydrogen and hydrogen will be identical, but their gravitational masses will differ due to matter-antimatter attraction. If the Athena project shows no difference in gravitational masses, the ZPE gravitation model is falsified. The good news is that my model can be falsified quite readily, unlike standard cosmology, which apparently cannot be falsified by any discordant observations. The ZPE gravitation model is simple, and it is based entirely on logic and on things we already know to exist (no additional entities need apply), and it may soon be proven viable or dead by Athena.

If the ZPE EM fields can be polarized by the presence of mass, Sakharof and others who suggested decades ago that the ZPE might be the source of gravitation and inertia will be taken seriously. Of course, to express forces in a field, the field will have to be capable of polarization. To my knowledge, these people never proposed a mechanism by which the ZPE fields might be polarized or densified. If they had pursued this, cosmology might look very different today.

Once it is shown that mass polarizes the ZPE EM field, inertia will be seen as a resistance to acceleration relative to the LOCAL ZPE field, and not the mysterious Machian effect where the acceleration is relative to EVERYTHING in the universe. Gravitation will be seen as force acting through local fields in Euclidean space, not as space-time curvature. It is this type of simplification of cosmology (with an actual mechanism to explain gravitation, this time) that will be required before cosmology (large-scale physics) can be reconciled with QFT. Occam's Razor leads me to believe that this simplification (get rid of curved space-time, dark matter, dark energy, etc) and its likely resolution of GR problems at extreme scales (cluster down to sub-atomic) is far more likely to be true than the repeated piling-on of mysterious entities that we have seen in recent decades. We know that the ZPE fields exist. Why posit the existence of dark matter and dark energy without first exploring the behavior of these fields with respect to embedded masses, gravity, lensing, etc?

I have been working on the ZPE gravity model for about a year, and will be willing to email a non-technical summary of it (my math skills are sorely inadequate, so it really is non-technical by necessity) to anyone who would like to look it over. Beat it up, bash it, etc - I welcome your comments, and I have thick skin as long as you only beat up the model and not me.

Apologies to Nereid and others who are sick of hearing this. I hate to annoy nice well-meaning people who believe in the infallibility of GR, but I am firmly convinced that GR's model of gravitation is wrong. A good approximation with wide applicability, but fundamentally wrong.

 

[Chronos]

A couple of thoughts. Inflation can be explained [including how it stops] using scalar fields. There is pretty good selection of papers on the concept. Here is an interesting recent entry:
http://arxiv.org/abs/astro-ph/0409071
I also share SelfAdjoints question of the source of conflict between GR and QFT. I personally feel GR is more nearly complete than QFT. GR is not the only theory that has compatibility issues with QFT, as SA noted.

 

[SpaceTiger]

The authors say that the lensing is consistent with the center of mass center of the clusters, which shows the presence of dark matter in the clusters and refutes the expectation (in MOND) that ram-stripped X-ray gas between the clusters should be expected to exhibit lensing effects.

Dark matter implies that there's mass that we can't see - i.e. that the center of mass would be in a different location from the light...which is exactly what you just said. This is not MOND-specific, it applies to any alternative gravity model. He just talks about MOND because it's the favored alternative model.

I am not refuting the lensing effects that they measured, nor the fact that the lensing effects are consistent with the centers of the clusters.

The whole point is that the lensing effects are inconsistent with the center of light in the clusters:

"The observed offsets of the lensing mass peaks from the peaks of the dominant visible mass component (the X-ray gas) directly demonstrate the presence, and dominance, of dark matter in this cluster."

Your model is very interesting and I look forward to see if its predictions are borne out, but you'll have to take into consideration evidence like that given above.

 

[SpaceTiger]

AFAIK, QFT can't be well-defined in curved spacetime, any more than GR can be perturbatively quantized. Is that what you mean by saying GR is inconsistent with QFT? Perhaps QFT is inconsistent with GR?

Yes. The reason we think GR would fail on small scales is that QFT seems to work and they're inconsistent. We have no means of testing gravity on those scales (at the moment), so we're just assuming that GR is the problem. I'm not an expert on quantum gravity, so that's about all I can say.

 

[Chronos]

The paper is an interesting and compelling refutation of MOND at cluster scales. The underlying observations are not a confirmation of the existence of dark matter, however. The existence of dark matter is inferred from the failure of GR to properly predict the cluster lensing and cluster member velocities. Further observations of this type cannot be regarded as independent evidence for the existence of dark matter. We know that GR cannot properly predict galactic rotation curves, cluster binding, or cluster lensing, given the luminous matter observed. Some of us are so certain that GR must be right that we are unwilling to challenge it, and so we have to invent entities to "balance the books".

Let's pretend that non-baryonic dark matter does not exist, and we have to observe the universe with the radiation, particles, matter, of the known classical universe. In that case, GR's gravitation model works extremely well on most scales. GR fails to be predictive on galactic scales and larger, however. If we resist the temptation to enshrine GR as "perfect" (and Einstein's made his views on epistemology very well known), we must admit the possibility that GR's gravitational model is flawed - a better approximation perhaps than the Newtonian model, but still not correct.

Agreed, the existence of dark matter is inferred. So what? The existence of gravity is also inferred by observation. And further observations of this type will be regarded as evidence for the existence of dark matter - at least by the scientific community. Inferring entities from observational evidence is not an 'invention', it is science. The whole point of making additional observations is to test those inferences. While some of us may be so certain GR is right we are unwilling to challenge it, others are so certain it is wrong, they are blind to the evidence it is not wrong. Just what are you saying here - is GR merely an 'epicycle' of Newtonian gravity?

 

[turbo]

Agreed, the existence of dark matter is inferred. So what? The existence of gravity is also inferred by observation. And further observations of this type will be regarded as evidence for the existence of dark matter - at least by the scientific community.

The point is that the existence of dark matter was proposed to bridge the gap between behavior predicted by the standard model and what is actually observed. There is no independant justification for dark matter, aside for the need to resuscitate GR and keep the BB theory alive. None.

Inferring entities from observational evidence is not an 'invention', it is science. The whole point of making additional observations is to test those inferences. While some of us may be so certain GR is right we are unwilling to challenge it, others are so certain it is wrong, they are blind to the evidence it is not wrong. Just what are you saying here - is GR merely an 'epicycle' of Newtonian gravity?

No. GR is a more useful approximation of gravitation, and is a bit more widely applicable than Newtonian gravity. It is not, however, a predictive approximation on the scale of galaxies and clusters, nor is it applicable at quantum scales.

Inventing entities based on the failure of the standard model to properly predict observation is not science, it is fantasy. For instance, I may look up at the sky and see Jupiter moving at rates that are not consistent with what I would expect from observing the stars. If I am diligent, I may be able to deduce that Jupiter is a distant planet orbiting the Sun. If I am dull or credulous (but imaginative), I may infer that Jupiter is being pushed back and forth by angels. Silly idea, but the idea is no less silly than the concept that some mysterious substance can cause galaxies to have flat rotation curves and make clusters appear to have WAY more mass than we can detect visually. Dark matter is no more credible than Jupiter's "angels" and is no more likely to be detected.

 

[Chronos]

You are correct. Dark matter is the best fit model that agrees with both observation and theory. While dark matter has not been directly observed, there are a number of observations that lead to the same conclusion - none of which are required to 'resuscitate' GR or BB. How is inferring dark matter a 'fantasy'? GR does not require dark matter, nor does BB. By your arguments, every unexplained observation somehow yields credibility to 'tired light', 'intrinsic redshift', and 'steady state cosmology'. I think not.

 

[turbo]

While dark matter has not been directly observed, there are a number of observations that lead to the same conclusion - none of which are required to 'resuscitate' GR or BB. How is inferring dark matter a 'fantasy'? GR does not require dark matter, nor does BB.

We differ here, my friend...GR absolutely requires dark matter. GR gravitation is not predictive on galactic scales, based on the materials we can sense out there. That is why dark matter was hypothesized in the first place - to close the gap between what GR predicts and what we actually observe. Without dark matter, GR is not predictive on galactic scales - what is troubling is just how much of it is needed to close the gap.

Furthermore, making more and more observations that confirm the failure of the predictive power of GR gravity at galactic and cluster scales does not confirm the existence of dark matter. Such observations refine our understanding of just how the GR model of gravity fails under specific circumstances and they help us quantify the magnitude of the failure (and that is not a worthless endeavor, by any means), but the observations do not confirm the existence of dark matter. That is simply not logical - it is a matter of faith.

 

[Gold Barz]

We differ here, my friend...GR absolutely requires dark matter. GR gravitation is not predictive on galactic scales, based on the materials we can sense out there. That is why dark matter was hypothesized in the first place - to close the gap between what GR predicts and what we actually observe.

Furthermore, making more and more observations that confirm the failure of the predictive power of GR gravity at galactic and cluster scales does not confirm the existence of dark matter. Such observations refine our understanding of just how the GR model of gravity fails under specific circumstances and they help us quantify the magnitude of the failure (and that is not a worthless endeavor, by any means), but the observations do not confirm the existence of dark matter. That is simply not logical - it is a matter of faith.

turbo-1 check your PM's

 

[hellfire]

AFAIK, QFT can't be well-defined in curved spacetime, any more than GR can be perturbatively quantized. Is that what you mean by saying GR is inconsistent with QFT? Perhaps QFT is inconsistent with GR?

I have read that even quantum field theory on classical backgrounds which do not have certain symmetries is not well defined, as there are multiple representations of the canonical conmutation relations which are not related by unitary transformations. Is this correct? Do you know where can I find a proof of that, or a discussion of this topic?

 

[Thor]

Hi all,

I've been struggling with an idea lately and was wondering if anybody could shed some light on it. It seems simple but i don't think the answer is very obvious.

The best guestimate for the age of the universe at the moment is 13.5 billion years old. If we could travel back in time 13 billion years and then measured the age of the universe again what would be the answer? Would it be 0.5 billion years old?

Thank you.

If you were born on a proton which once was part of a nuclear bomb and the bomb had exploded prior to your birth, you would probably think the result of that explosion is all there is of the Universe - and that the Universe 'occured' on the date and time of the explosion.

You would be wrong.

 

[Scinan Heorte]

I believe it is a mistake to assume that any age of the universe should be applied to all regions. I see the universe as a wholly dynamic environment in which a wide range of ages is possible. Where expansion rates are different from one portion to the next and presumptions concerning its size and age are far too easily made and included in calculations. Current estimates are dependant upon the presumption of a linear and static environment of unchanging conditions which has been as it is now since the begining. I feel this is wrong.
So far as your question goes, when you went back 13 billion years, did you take the universe with you? Last I heard, the hypersurface was an average of 13 billion years out from that point. I wonder would there be anything there but the void of time itself.
So far as an infinite universe is concerned, I do not see an infinite universe. I see a universe of finite energy and finite size expanding outward in a definable hypersphere of limited proportions. I see irregularities to it and non-linearities which make things difficult to understand, and I see difficulties in pinpointing the exact location within the void of time the big bang occured, but I do not see unimaginable and limitless issues to get lost in.
I do however get seasick in the shift of perspectives involved.

 

[1123581321]

depends on what we find the Hubble constant to be (assuming big bang is correct and acceleration of universe is constant) (which yes, big bang is correct and yes, the acceleration of the universe is constant). If it is 50, then the universe is around 15 billion years old. If it is 80 then the universe is around 8 billion years old (the latter of the two is highly disputed, because we have found stars which we estimate to be older than 8 bill). mostly people think it is around 15 billion years old

Fibonacci