Universe May Contain “Tardis” Regions Bigger On The Inside Than The Outside
medium.com
medium.com
I stopped reading here:
"But just over a decade ago, astronomers noticed that the most distant galaxies were accelerating away from us much faster than the ones nearby. In fact, the further they looked, the greater the acceleration seemed to be."
This was, in fact, noticed in 1917 by Vesto Slipher, derived from General Relativity by Georges Lemaitre in 1927, and further confirmed by Edwin Hubble in 1929, when it became known as Hubble's Law.
We found this out by very precisely measuring the brightness of a very specific type of supernova, a Type Ia supernova, which has a very consistent intrinsic brightness (about 5 billion times brighter than our Sun) allowing for distance measurements with an uncertainty of just 5%. This was a novel achievement, enough to merit the 2006 Shaw Prize in Astronomy.
>Current evidence suggests the expansion of the universe is accelerating (see Accelerating universe), meaning that for any given galaxy, the recession velocity dD/dt is increasing over time as the galaxy moves to greater and greater distances; however, the Hubble parameter is actually thought to be decreasing with time, meaning that if we were to look at some fixed distance D and watch a series of different galaxies pass that distance, later galaxies would pass that distance at a smaller velocity than earlier ones.[33]
In short, if you launch a unpowered projectile upward at close to the speed of light, Einstein's prediction of gravitational time dilation (experimentally confirmed) in turn predicts that the projectile accelerates away from you, for as long as its velocity relative to you is close to the speed of light.
(The ivory tower no longer considers ideas that source outside the tower, which explains why this idea is in a blog.)
<quote> 2. Herein, as in most relativity texts, we ignore the travel time of light that prevents a remote event from being seen until after it has occurred. In principle a network of observers can be set up in locally inertial frames that momentarily co-move with the rocket, so that events can be detected by equipment right next to them, and the records subsequently compiled and analyzed. </quote>
I could be reading that wrong, but the author seems to be suggesting that time's inherent inconsistency at relativistic speeds and distances can be mitigated with a "network of observers". I don't know if that's true, but "momentarily co-move with the rocket" sounds like it's ignoring an awful lot of relativistic acceleration of the measuring devices.
if you launch a unpowered projectile upward at close to the speed of light, Einstein's prediction of gravitational time dilation (experimentally confirmed) in turn predicts that the projectile accelerates away from you
In other words, the "acceleration profile" produced by this model is: acceleration, then deceleration. But the "acceleration profile" that needs to be explained for our actual universe is deceleration, then acceleration: an apparent slowing down of the universe's expansion, followed by an apparent speeding up. There's no way to get that out of the blog post's model.
The "deceleration, then acceleration" is an implication based on assumptions, not something observed. We haven't actually witnessed any deceleration or acceleration when looking through a telescope. Instead, when we look at various distances from the Earth we see various redshifts (not changes in redshifts), and then, because looking further away is looking back further in the history of the universe (a safe assumption), and based on the assumption that space itself is expanding to cause those redshifts and any changes in those redshifts, we conclude that space itself expanded in a decelerating manner and then, later in the universe's history, in an accelerating manner.
The blog implies that we should rethink those assumptions. It shows that the expanding space paradigm is superfluous. When that paradigm is removed, generally accepted equations can be applied to show that objects sufficiently far away from us (which we can now assume are receding at close to the speed of light, given their high redshifts) accelerate away from us. So when we look close to us we'll see evidence of deceleration, and when we look further from us we'll see evidence of acceleration, but that has nothing to do per se with the history of the universe. Thus the blog does explain the observations that form the acceleration profile you note.
Really? What is your source for this extraordinary claim? You yourself said that the equations you used are generally accepted. That means people already understand their consequences. The fact that people don't agree with you about how to apply the equations in a particular scenario doesn't mean people don't believe the equations.
The blog explains the acceleration away of supernovae
No, it doesn't, because its prediction is not the same as what we actually observe.
The "deceleration, then acceleration" is an implication based on assumptions, not something observed
No, the apparent deceleration, then acceleration is what we actually observe. The question is how to interpret these observations. The standard interpretation is that the deceleration, then acceleration are real, not just apparent. Your interpretation is that they are only apparent; but your model can't even reproduce the apparent profile we observe, so your interpretation is not supported by its own model.
So when we look close to us we'll see evidence of deceleration, and when we look further from us we'll see evidence of acceleration
No, you have it backwards. When we look close to us, we see evidence of acceleration (because we're looking at what happened more recently in the universe's history), and when we look farther away, we see evidence of deceleration (because we're looking at what happened earlier in the universe's history). Your model does not reproduce that observation, so it's not a valid explanation.
I'll respond only to this, as I've found here and before that you don't discuss fairly; that's unfortunately common in discussions about physics.
It's logically impossible to provide a source to show that something isn't recognized elsewhere. (This should be obvious to a smart person such as yourself, which is in part why I say you don't discuss fairly.) But you can search all you want to see that the claim cannot be found elsewhere.
That equations are generally accepted doesn't necessarily mean that people already understand their consequences. Understanding their consequences requires also experimenting with the equations in sufficiently various ways. Apparently that wasn't done until the blog author did it, or else I'd likely be able to do a Google search to find elsewhere that acceleration away can be shown by those equations. I'm confident that millions of science students would find "an unpowered projectile launched upward can accelerate away" highly interesting (maybe as well the physicist quoted in the blog post, who is mystified as to how his keys thrown upward could accelerate toward the ceiling). It should be an easy search if it was previously known.
You're entitled to your opinion, but I'm also entitled to mine, and since we're being open and honest I'll give it. My opinion is that you are not interested in actually understanding the mainstream theories of physics that you are criticizing (and neither is the author of the blog post you linked to); you are only interested in criticizing them.
But you can't honestly criticize a theory that you don't understand; that means that before you criticize a theory, you must be able to explain what it says (even if you think that what it says is wrong) in a way that its own proponents agree to. I haven't yet seen you do this (and the author of the blog post you linked to doesn't either). See further comments below.
Understanding their consequences requires also experimenting with the equations in sufficiently various ways.
I agree with this in principle, but there aren't enough people or enough time to check all the consequences. So it's not a huge achievement just to calculate a new consequence; you need to show that it's significant. See below.
And for the record, I also agree that the model in the blog post correctly applies the equations (although as you and it are using the term "acceleration", it should more properly be "coordinate acceleration"). I just don't agree that this model can explain our observations of redshifts and apparent brightness of distant objects, since its predictions don't match our actual observations of the universe.
Apparently that wasn't done until the blog author did it, or else I'd likely be able to do a Google search to find elsewhere that acceleration away can be shown by those equations.
Okay, let's assume you're right that nobody has ever done the precise calculations that the blog post's author did, before he did them. If you had said just that--that mainstream physics has never considered the calculation the blog post author did before--I might still have been a bit skeptical, but I probably would have let it pass. Your claim came across as a stronger claim than that; you appeared to be claiming that, if you showed the blog post's calculation to a mainstream physicist, they would say it was wrong--not wrong as in not applicable to the expansion of the universe, but wrong as in incorrectly calculating the consequences of the relativistic rocket equation.
I strongly doubt that is the case, since, as I said above, I agree that the blog post author has calculated the correct numbers using the relativistic rocket equation (even though I don't agree with his application of those numbers to a different scenario). I strongly suspect that if you showed the blog post calculations to a physicist familiar with relativity (such as the author of the relativistic rocket equation page in the Usenet Physics FAQ, which the blog post links to), they would react the way I did: yes, this is a correct calculation using the relativistic rocket equation, but it's not relevant to the expansion of the universe. So saying that "generally accepted physics doesn't recognize that an unpowered projectile launched upward can accelerate away" does not, I think, describe what mainstream physics says in a way that a mainstream physicist would agree to.
This is another way in which the blog post incorrectly describes the mainstream theory. (Trying to arrive at a good description of what a theory says based on a sound bite in a non-technical article is a waste of time anyway; you need to look at the actual technical literature.)
In the blog post's model, the apparent acceleration up towards the ceiling is achieved by launching the keys upward at almost the speed of light. But in the mainstream dark energy model, if our spacetime locally was dark energy dominated, you could release the keys at rest relative to you, and they would accelerate, in the coordinate sense, up towards the ceiling (instead of accelerating, in the coordinate sense, down towards the floor, as you would expect with normal gravity). That's what the physicist quoted in the NatGeo article was actually describing.
The redshifts are not the only evidence we look at; we also look at the relationship between apparent brightness of objects and their redshifts. See Ned Wright's cosmology FAQ for a good brief overview:
Space ("bigger") and time are interrelated concepts (same damn thing/Minkowski vector) - if you have less time in an area (i.e. due to a gravity well, like Earth's) you can equally view it as more space.
Ergo, the "volume" of "space" measured from within Earth's gravity well out to a fixed distance (say EML-1, for the sake of argument), differs to the same volume as measured from outside of the gravity well.
There's also another way of looking at their hypothesis. If cosmic voids have less space in them (i.e. more time) (if you don't have any matter-energy in a volume, then what "keeps" time?), this would explain redshift pretty neatly in terms of the refractive index of space-time. Beats the hell out of dark matter and dark energy, both of which are fudge-factors for a fundamental facet of the nature of the universe which we Do Not Understand yet.
It's all relative.
The metric in a gravity well like Earth's is not the Minkowski metric, so you can't interpret gravitational time dilation (which is what you are referring to by "less time" in a gravity well) the same way you would interpret time dilation in special relativity. The simplest way to see this is to observe that gravitational time dilation is present even when everything is at rest relative to each other, whereas time dilation in special relativity requires relative motion.
the "volume" of "space" measured from within Earth's gravity well out to a fixed distance (say EML-1, for the sake of argument), differs to the same volume as measured from outside of the gravity well.
This is not correct as you state it. What is correct is that the volume you measure depends on your state of motion: the volume of space you will measure out to a certain radius from the Earth will be larger if you are at rest relative to the Earth than if you are free-falling inward towards the Earth. But two observers both in the same state of motion will measure the same volume of space out to a fixed radius from the Earth, regardless of their location relative to Earth's gravity well.
If cosmic voids have less space in them
This isn't consistent with their hypothesis; their hypothesis is that the voids have more space in them, not less. So you can't combine this with anything in their model to get a valid answer; you're starting with inconsistent premises.
(i.e. more time)
Less space does not mean more time; see above.
(if you don't have any matter-energy in a volume, then what "keeps" time?)
The voids don't have zero matter-energy; they just have a lot less than other parts of the universe (at least, according to our best current observations.) That said, spacetime itself can "keep time" even if there is no matter-energy present in a particular location.
> Lavinto and co say that when light enters a Tardis region, it is deflected sharply by the greater curvature there. That’s not what astronomers observe at all
Given that "light" is, I believe, our only way to observe the universe, how can one tell that it is not deflected?
I mean if for instance the heliosphere had some unknown refractive properties, how could we discover it since we only have light to determine the position of objects outside of the solar system?
We can't easily detect small amounts of deflection in distant parts of the universe because, as you say, we usually have nothing to compare our observations to. (In the case of light being deflected by the Sun's gravity, we can compare how a certain part of the sky looks--i.e., a certain particular grouping of stars--when the Sun is in that part of the sky, vs. when it isn't, and measure the deflection that way. But for light deflection in distant parts of the universe, there's no easy way to do that.)
However, the presence of large amounts of deflection would show up easily: we would frequently see multiple images of the same objects. In fact we only see such multiple images rarely, which indicates that there aren't any regions of large light deflection in our universe.
if for instance the heliosphere had some unknown refractive properties, how could we discover it
The same way we discovered that the Sun's gravity bends light. See above.
That will only tell us about redshift/blueshift; it won't tell us anything about what path the light took to get to us.
That said - re: the measurement of a volume within a gravity well - how would you measure said volume? If you were to use light, surely it would take more time from an external reference frame to traverse (external chronometer) than it would within (internal chronometer), ergo meaning that the space is equivalently larger to the decrease in the time vector (as you can only convert space into time and vice versa).
Re: voids - I know that their hypothesis is that there's more space in the voids - but why could it not equally be the fact that there is less? More time (due to very low mas density/near-absence of gravity), ergo less space - and therefore redshift due to photons decelerating relative to our frame of reference (but constant v of c in theirs) as they move back into "normal" space.
Re: spacetime "keeping time" - true - but that also depends on your premises :) I like loop quantum gravity, and view time as an entropic thermodynamic process which can't exist without interactions... although the lack of quantisation jitter seen from pulsar light suggests that this might be wrong.
Make a lot of local measurements of small volumes, and add them up. (Yes, I know we can't actually do that with voids a billion light years away; but when the Tardis paper talks about "volume", as I read their math, that kind of measurement is what they mean.)
If you were to use light, surely it would take more time from an external reference frame to traverse (external chronometer) than it would within (internal chronometer)
This is true, but I do not think it means what you think it means. See below.
ergo meaning that the space is equivalently larger to the decrease in the time vector (as you can only convert space into time and vice versa)
This doesn't make sense to me. Can you give a reference or show some actual math?
I know that their hypothesis is that there's more space in the voids - but why could it not equally be the fact that there is less?
I didn't say there couldn't be less; I said that assuming that there was less would be inconsistent with their hypothesis (which is that there is more), so it makes no sense to combine that assumption with their hypothesis and expect a sensible answer.
that also depends on your premises
The "Tardis" paper assumes the same premises, so it seems reasonable to keep them when discussing the paper.