

Universe May Contain “Tardis” Regions Bigger On The Inside Than The Outside - kentuckyfc
https://medium.com/the-physics-arxiv-blog/f9a65d6fe175

======
goodside
[Edit: Never mind -- I completely misread the quote, as JumpCrisscross points
out.]

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.

~~~
fargolime
Discovered in 1998, and explained in 2008 using generally accepted equations,
at [http://finbot.wordpress.com/2008/03/05/dark-energy-
obviated/](http://finbot.wordpress.com/2008/03/05/dark-energy-obviated/)

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.)

~~~
dTal
I can't pretend to understand relativity well enough to verify that blog
post's maths, but one of the notes caught my eye:

<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.

~~~
fargolime
The network of observers are moving inertially (i.e. unpowered, freely
falling), moving with the rocket for only a moment, so they're not
accelerating like the rocket is. That's how those observers can make good
measurements, in that moment. For more info search for "momentarily comoving
inertial frame" at
[http://math.ucr.edu/home/baez/physics/Relativity/SR/clock.ht...](http://math.ucr.edu/home/baez/physics/Relativity/SR/clock.html).
Each inertial clock can measure the passage of time accurately.

------
madaxe
But of course. We reside in one of them.

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.

~~~
pdonis
_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._

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.

~~~
astrobe_
Since you seem to have some insights on the topic -- the article points out
that

> 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?

~~~
yk
We measure spectra. So there would be no way to measure the redshift of a
single wavelength, e.g. a laser, but since we have the full spectra, we can
measure the relative position of spectral features and the wavelength of these
features to compare them with laboratory measurements.

~~~
pdonis
_we can measure the relative position of spectral features_

That will only tell us about redshift/blueshift; it won't tell us anything
about what path the light took to get to us.

~~~
yk
Yes, but that is a rather general problem. Best you can do is to look at the
so called Lyman-alpha forest, which gives you essentially the mass
distribution along the path. And this gives you a good estimate for the
deflection.

~~~
pdonis
The mass distribution isn't necessarily a good proxy for the deflection. Lyman
alpha lines are from absorption by hydrogen gas clouds; the average effect of
those on the path of light is likely to be close to zero, because the clouds
are diffuse and more or less homogeneous (i.e., their average density on large
length scales is pretty much the same everywhere). The "Tardis region" model
requires large deflections of light at the boundaries between the "Tardis"
regions and regions of normal density, which will not average out since there
aren't enough such boundaries between us and the distant supernovas that are
our main line of evidence for the accelerating expansion of the universe.

~~~
yk
I did not read the tardis paper, but the mass distribution gives you at least
a upper limit, in the sense that if there is not much mass in one direction,
then there is also not much deflection. At least in more or less normal
models.

~~~
pdonis
In more or less normal models, yes; but as I read the Tardis paper, the whole
point is that it is _not_ a more or less normal model.

