Cosmologist claims Universe may not be expanding (2013)
nature.com
nature.com
This is true in so-called scale invariant theories. These theories do not contain any intrinsic length scale. The moment your theory contains a fundamental length l you break scale invariance. In this case you are able to compare your yard stick to the length l to find out if your yard stick was shrinking or the universe really is expanding.
Our present model of the world still contains a few fundamental length scales (such as the Planck length, or a length scale associated to the nuclear force), but people such as Christof Wetterich are building models that try to get rid of (some of) these fundamental length scales. A major approach in this direction is asymptotically safe quantum gravity, that also led Christof Wetterich and Mikhail Shaposhnikov to the most precise prediction of the Higgs mass prior to the Higgs' discovery in 2009, see https://arxiv.org/abs/0912.0208.
If we create a light year long line of yardsticks then we would expect the line to expand faster than the yardsticks that make it up. Locally this would look like growing gaps between the yardsticks. we never used the fact that the line was a light year long. So let's just put two yardsticks next to each other in a vacuum. They drift apart and eventually so far they are not part of each others' observable universes.
Doesn't that imply that the accepted model can't be tested? I mean, in the sense of distinguishing it from this one.
It's not "out of favor" just as a matter of fashion: a lot more data was collected, extending much further away and therefore much further into the past.
> a few more new facts just might swing things the other way again.
No, it would take a lot more than that, because our current model of accelerating expansion for the past few billion years (note that before that, the expansion was decelerating) is based on a lot more data than we had 40 or so years ago.
Afaik, we have no direct observations of galaxies moving away from us - over such enormous distances we have not had enough time since the start of observations to actually see a galaxy recede.
The change in wavelength is exactly proportional to the increase in size of the universe during the time of flight, and it is not directly related to speed of recession except in common and inaccurate discussion. The link to relative velocity (if that concept makes sense for objects in widely separated and unrelated reference frames) is model dependent, while the metric expansion measurement is directly measured.
In my opinion the reasonable way to deal with that, is to assume that they are the same model since they describe the same physics and leave the semantics to the philosophers.
This one, though. I mean, the fundamental observation is that red shift increases with distance. The accepted model has red shift caused by motion away from us, and so we conclude that recessional velocity increases with distance. That is, the Universe is expanding.
This new model has blue shift caused by increasing mass. And so we are blue-shifted relative to distant stuff, which we see only in the past. So it looks red-shifted to us. And distance is proportional to time delay, so stuff that's farther away is more red-shifted.
Bu I don't see how the temporal rate of mass increase could be related to -- or rather, another reflection of -- the expansion of the Universe. But then, IANAP, so hey.
It actually proposes a plate tectonics model where the continents all fit back together as you shrink the Earth and it kind of works.
AFIAK the hypothesis contradicts too much other data and is likely wrong, but I count it as an example of a good creative out-there hypothesis. This kind of thinking is good in general.
Basically, if stress-energy is locally conserved, particle masses can't just increase out of nowhere: the energy that goes into the increasing masses has to come from somewhere, and so the overall energy, which is what drives the dynamics of the universe, doesn't change, so the model can't predict anything different from standard cosmology.
OTOH, if stress-energy is not locally conserved, then we should be able to observe such violations of conservation. But no such observation has ever been made: we have extremely strong evidence of local stress-energy conservation.
Can you observe tiny scale invariant change in just few hundred years?
> model can't predict anything different from standard cosmology.
I think that's the goal of emergent scale symmetry at this point. Alternative to standard cosmology that explains the same things. To differentiate between the two you need to figure out what is different.
Dark energy does not "come from nowhere". It's locally conserved everywhere. It has to be: the covariant derivative of the metric is identically zero, and the "stress-energy tensor" of dark energy is just a constant times the metric.
As to looking at older galaxies - maybe - but if the relativistic mass of photons is also changing due to the same phenomenon, there would be no difference in observations.
For instance size of hydrogen atom is inversely proportional to the mass of electron [1], so with heavier electrons, sizes of atoms shrink.
And in general in units where planks constant and speed of light are equal to one, mass is measured in 1/length.
So, yeah, we should be able to measure a gradual emission spectrum shift here on Earth with current methods - we can measure energies of photons to very high precision, and you’d likely only need a few years of data to prove or disprove the hypothetical cosmology.
If it’s expanding, what is it expanding into?
Maybe akin so asking: "What came before time?". The question itself is a contradiction.
Infinite Universe
https://www.amazon.com/Infinite-Universe-Theory-Glenn-Borcha...
I think you should start with:
https://en.wikipedia.org/wiki/Observable_universe
And only then with:
https://en.wikipedia.org/wiki/Shape_of_the_universe
In short, what can ever influence "our" part of the universe is limited by the speed of light being constant and being the physical "speed limit", and by the fact that the age of the universe is less than 14 billion years. (Earth alone is 4.5 billion years old).
Fascinatingly enough, we can "see" in each direction we look at up to the distance of around 46 billion light years, even if the age of the universe is just 13.8 billion years (that 46bly in one direction is the result of the accumulated expansion of the universe since the beginning). And the farthest things we see are also the oldest, as we effectively "look back in the past" when we look at the distance (due to the speed of light being constant). So when we look far enough we see almost up to the beginning of the universe (up to the point when the universe was "clear enough" for us to see after the beginning). The CMB (Cosmic Microwave Background) is the "leftover glow" of the big bang that reaches us now, from that earliest past:
https://medium.com/starts-with-a-bang/this-is-how-we-know-th...
Then one can try to guess what's there behind the physical limits that are fixed for us, but we will never have the direct data about that:
https://medium.com/starts-with-a-bang/ask-ethan-how-large-is...
That’s some serious retro-causality if a photon from 13B ly hits us instead of Andromeda.
This is similar to a situation where you draw a set of perpendicular axis on a plane and use them to give coordinates (x, y) to a point. You then rotate the set of axis, keeping the point fix. Your question about the energy amounts to asking "what happens to the x-coordinate of that point?".
The best modern atomic clocks depend on atomic spectra, a shift in which would be evidence for or against this model.
Given the precision of modern atomic clocks (<10^-17)[1] and the fact that the galactic spectral shifts are significant at large distances this seems plausible. I don't have precise #'s to do the calculations at hand so maybe I've made an error.
https://en.wikipedia.org/wiki/Fine-structure_constant#Is_the...?
If the fine structure constant α is found to change, then would only be able to say that the relationship among the speed of light c, the elementary charge e, and the Planck constant ħ are changing, but IMO if we discovered that (say) α changed from .007300… to its present value of .007297…, we would not be able to then say "the speed of light changed (and the elementary charge and Planck constant remained the same)"
…but as a matter of practicality, scientists could feel free to use a different value for c in the past (and the present value for the elementary charge and Planck constant), if that is the most convenient way to accommodate a change in α. It wouldn't surprise me in the least if holding c and ħ constant is better for astronomers and holding e and ħ constant are better for particle physicists.
(Saying that ħ changes would be similar to saying that mass changes, or at least, the units of ħ include mass, and the Planck constant "is the basis for the definition of the kilogram." in the SI system [well, technically, this is not the case until next month. Right now the kilogram is still defined by the physical "international prototype kilogram" object, but the above quote is from wikipedia])
However, while the best experiments are consistent with changing α, the change in α is constrained to be WAY less than it would need to be to explain cosmological red shift observations.
I've read things (outside of the OP) that say the universe is expanding and also speeding up it's expansion, as neighbors exert less of a pull on each other the further spread out things get. However, that gravitational pull is still there -- will it at any point slow down the expansion and retract back inwards?
No. If we are talking about the current best model we have of the universe, the dark energy density (which is what drives the acceleration of the expansion) is constant in time, while the density of matter (which is what causes the expansion to decelerate) decreases with time. Up until a few billion years ago, the expansion was decelerating, because the density of matter was high enough to dominate. But since a few billion years ago, the density of matter has been small enough that the dark energy dominates, and that is never expected to change.
We already have inflation and dark energy but no good reason to expect either of them to be there at all. Like, the book on dark energy I’ve seen go: ”here are a bunch of pretty good guesses”, thats not a field full of confidence in its expectations (though admittedly the book is 9 years old by now).
I have seen plenty of heuristic arguments for why we should expect inflation to be there, but I'm not really qualified to judge. None of them seem to have convinced enough physicists to be considered standard.
For the cosmological constant, I think it depends on what you consider the "natural" condition to be. The simplest way to derive the Einstein Field Equation is to start from the Einstein-Hilbert Lagrangian and vary it with respect to the metric. The justification for using the Einstein-Hilbert Lagrangian is that it contains the only scalar which contains up to second derivatives of the metric and is quadratic in the metric and its derivative, namely, the Ricci scalar. But that statement is not actually true: there's another obvious scalar that meets this requirement, namely a constant. So the most "natural" version of the Einstein Field Equation contains the cosmological constant: it should be there on theoretical grounds, and that means "dark energy" should be there as well.
Of course that also raises another problem, which is indeed one we don't have a good answer to at present: why is the cosmological constant so small?
No. Even if dark energy stopped right now, almost ever pair of galaxies has long reached escape velocity. Their relative speed will slow over time, making them drift apart slower, but it will never reach 0, or even become negative (= contraction).
> If all masses were once lower, and had been constantly increasing, the colours of old galaxies would look redshifted
Can anyone explain this apparent contradiction?
lightweight is red, heavy is blue
If everything constantly grows heavier then the past is red and the future is blue.
So the timeline according to this theory is [Big Bang] - >[Inflation] - >[Increase in mass] & we're seeing the redshift from that?
Head hurts, I love it.
Does this view imply that new energy is appearing in the universe?
Does that means that the universe can't be considered a closed system and entropy increasing is not unavoidable?
The Steinhardt and Turok preprint is at https://arxiv.org/abs/hep-th/0111030 , published in the journal Science at http://science.sciencemag.org/content/296/5572/1436.full .
> We propose a cosmological model in which the universe undergoes an endless sequence of cosmic epochs each beginning with a ‘bang’ and ending in a ‘crunch.’ The temperature and density are finite at each transition from crunch to bang. Instead of having an inflationary epoch, each cycle includes a period of slow accelerated expansion (as recently observed) followed by slow contraction. The combination produces the homogeneity, flatness, density fluctuations and energy needed to begin the next cycle.
See also https://en.wikipedia.org/wiki/Paul_Steinhardt#Cyclic/ekpyrot... .