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wg48
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Myth of Streching Space
This is a follow on from a discussion on stretching space, which I claimed was a myth, in a thread called antimatter question
While trying to understand the unusual redshift formula (its not the usual relativistic one) used in cosmology I happened to read lots of statements
about space expanding or stretching causing the redshift of distant galaxies. In one article about the curriculum of an institute on astronomy and
cosmology it categorically stated the galaxies were stationary and that the red shift was due to the space stretching between them. No “sort of”
or “considered to be” no caveat at all. This was particularly crazy as in a different section of the same article it had a good explanation of how
the universe’s evolution is modelled as an adiabatic expansion of a fluid/gas. It explained that due to the large scale of the universe relative to
its contents it behaves as gas. The implication is that the expansion is powered by the internal pressure of matter and radiation. ie the galaxies are
pushed apart and move away from each other. with a velocity.
Oh and lots of statements in various notes that SR is not applicable though one did say it was SR and GR and that GR was an extension of SR. The
correct view IMHO.
I also happened on just one anti stretch note written by at least one professor of physics. Yes just one note. The myth is in deep. The note is not
popsci. Below is part of the intro.
The first anti stretch note I read must be about 20 years ago. I think the first pro stretch note I read was in Scientific America probably in the
sixties or early seventies.
https://arxiv.org/pdf/0808.1081.pdf
“A common belief about big-bang cosmology is that the cosmological redshift cannot be properly viewed as a Doppler shift (that is, as evidence for
a recession velocity), but must be viewed in terms of the stretching of space. We argue that, contrary to this view, the most natural interpretation
of the redshift is as a Doppler shift, or rather as the accumulation of many infinitesimal Doppler shifts. The stretching-of-space interpretation
obscures a central idea of relativity, namely that it is always valid to choose a coordinate system that is locally Minkowskian.”
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aga
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We are fundamentally wired to view things in terms of the 4 dimensions, namely Volume and Time, i.e. Where and When.
Attempting to view Reality in terms of the Other dimensions tends to make the mind meltdown.
I've tried to think through dimensional re-referencing and ended up in a state of demention.
What appears (and can be measured) in the usual 4 dimensions can also appear as chaos if it is observed purely in terms of the other relevant
dimensions that matter certainly occupies.
For example : if a certain particle always moves by X metres when a force of Y is applied to it, we can call it a Law of Physics.
This assumes that a Huge number of other variables remain fixed to earth conditions.
Under other conditions the same force could make the particle sing an opera, become an entirely new universe, or simply cease to exist.
Whatever the viewpoint, it does what it does.
Understanding with any precision the Why or How is certainly a distant possibility.
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wg48
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The note I posted the link to above is well written I would give it popsci and BS rating of 0,0 and 10 out of 10 for readability. I think they could
have been more condemning but I guess physics professors don’t do that.
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clearly_not_atara
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The paper opens with the following:
| Quote: | | We wish to make clear at the outset that we are not suggesting any doubt about either the observations or the general-relativistic equations
that successfully explain them |
I.e. it is a semantic quibble about the meaning of the words "stretching of space". However, the paper does not dispute the existence of dark energy.
http://en.wikipedia.org/wiki/Dark_energy
Mind you, the paper is not bullshit. But it does not actually address any concerns which are of interest to a layperson, nor does it reveal a
conspiracy or misunderstanding in the physics community. Rather, it addresses problems in physics pedagogy related to the use of analogies,
problems such as this one:
| Quote: | On the contrary, one of the most important ideas of general relativity is that spacetime is always locally indistinguishable from the (non-stretching)
spacetime of special relativity, which means that a photon doesn’t know about the changing scale factor of the universe.15The emphasis in many
textbooks on the stretching-of-spacetime interpretation of the cosmological redshift causes readers to take too seriously the stretching-rubber-sheet
analogy for the expanding universe. For example, it is sometimes stated as if it were obvious that “it follows that all wavelengths of the light
ray are doubled” if the scale factor doubles.
10Although this statement is correct, it is not obvious. After all, solutions to the Schr ̈odinger equation, such as the electron orbitals in the
hydrogen atom, don’t stretch as the universe expands, so why do solutions to Maxwell’s equations? |
This paragraph identifies a problem with the colloquial interpretation of the concept of stretching space as it is used to teach the theory
of general relativity to undergraduates. It is a little bit hilarious that someone who does not know quantum mechanics would consider a paper like
this one to be "very readable" considering that it is not possible to correctly understand the point being made in this paragraph if you do
not know what the Schrodinger equation is or how it relates to the orbitals of a hydrogen atom. Furthermore it is not likely to make much
sense unless you have already crossed the mental hurdle of viewing physical phenomena as solutions to differential equations, which is a concept the
authors clearly expect their readers to have internalized.
| Quote: | | it categorically stated the galaxies were stationary |
One difficulty in the "readability" of advanced physics articles for laypeople reading them is the use of words that don't mean what you expect them
to mean; in this case, "stationary" means that there are no forces acting on the galaxy whereas to a layperson "stationary" means that an
object has the same velocity as the ground wherever they are on Earth. The advanced physics version of stationary is true although the galaxy does not
have the same velocity as the ground where I am standing; what is being said is that the apparent acceleration of the galaxy is not due to
forces acting on it but due to space expanding between us and the galaxy. And because the apparent acceleration of the galaxy opposes the
gravitational force on the galaxy, its relative velocity to us is due to the history of space expanding between it and us, even though the Doppler
shift may be related to this velocity in a purely kinematic sense.
In closing: you are wrong.
[Edited on 04-20-1969 by clearly_not_atara]
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SWIM
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Quote: Originally posted by clearly_not_atara  |
...in this case, "stationary" means that there are no forces acting on the galaxy...
... And because the apparent acceleration of the galaxy opposes the gravitational force on the galaxy...
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So are there forces acting on the galaxy, or aren't there?
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phlogiston
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The expansion of the universe as a whole is fundamentally not different from the local deformations of space by e.g. gravity (even though the cause
and scale may be different), say around the sun or earth. We all know the effects of gravity are experienced as a force and resulting acceleration.
So, yes, I think the the expansion of space indeed results in a force/acceleration by galaxies and all other matter.
I've always found it odd that when space 'stretches', we apparently get more space. Where does it come from? Does it get added to our regular space
uniformly? Does that take energy?
And conversely, when a large mass cause the space around it to contract... where did the space go? Does the sun suck up a little bit of space?
Finding answers to questions like these ends with our limited understanding of what 'dimensions', 'distance', 'force', etc really are. How does the
universe encode distance?
There are theories for instance about how our macroscopic perception of 'distance' is actually the result of the level of entanglement between the
matter in the two parts of space, etc. Really cool and interesting.
Lots of fun trying to imagine expansion of space in terms of concepts like this.
[Edited on 27-10-2017 by phlogiston]
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"If a rocket goes up, who cares where it comes down, that's not my concern said Wernher von Braun" - Tom Lehrer |
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aga
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A Huge problem for us is that we can prove/disprove a hypothesis based on experimental evidence and/or calculations.
Where we are is like an observer looking though the keyhole of a door and observing what is beyond that door.
We have technologies that can peer through that keyhole and take precise measurements, on which data is built, hypotheses are discarded, or upheld to
eventually become Theories.
For example:
We observe (in the field of view we have) that the room behind the door contains a wooden floor and a flat rear wall, and measure all of it with high
precision, including material composition, light intensity, atmosphere composition, heat etc etc.
From this mass of 100% scientific data we can conclude many things, such as the volume of the space behind the door.
Some genius (or idiot) comes along, opens the door, and we now see it is merely a stage set for the musical "Cats" in a Vast West End theatre.
The Data was all good. The Science was all good. The hypotheses were correctly proven/disproven. The resulting theories were independently verifiable.
The maths were perfect. We were Not Wrong: just incomplete.
All theories stand to be amended or even replaced as new evidence appears.
"What goes Up must come Down" is an example (and i doubt Newton imagined the 'down' part happening megayears later)
He only missed out the " ... unless it goes up with enough energy to escape the earth's gravitational pull" part.
Einstein, Newton, Copernicus, Galileo etc were all able to think outside the box, and gave us very valuable information.
I do worry that people learn a Theory and cling to it as if it were the Word of God.
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wg48
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Your reference to the note not denying dark energy and your comment “a semantic quibble” suggests you don’t understand the controversy or the
note. I suggest you read the note again more careful and the other notes referenced if you want a better understanding. I was also going to suggest
you swot up on physics and the scientific principal (the one that requires evidence and testable predictions). But that apparently has not always
worked. Perhaps you need a better BS detector.
“No conspiracy” where did that come from ?. Did some one suggested there is a secret sect of Pi masons who spread unscientific phenomena in
attempt to confuse undergraduates? (humour).
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Melgar
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| Quote: Originally posted by wg48 | I was also going to suggest you swot up on physics and the scientific principal (the one that requires evidence and testable predictions). But that
apparently has not always worked. Perhaps you need a better BS detector.
“No conspiracy” where did that come from ?. Did some one suggested there is a secret sect of Pi masons who spread unscientific phenomena in
attempt to confuse undergraduates? (humour).
|
First of all, I'm glad to see that you're investigating this matter, rather than just writing off everyone that contradicts you as being idiots.
Second, the trouble with astrophysics is that we can only observe the universe from a single point, and thus while we can observe many strange and
interesting phenomena, it is often the case that it is barely within our power as a species to observe them, let alone reproduce them under
experimental conditions. The best we can hope to do is to describe them using a model that people are able to wrap their heads around. The
"inflation" model of the universe is a model and nothing more. It is a way of describing phenomena to other people. The paper you
referenced describes shortcomings in a common use of this model, and ways in which the model is relied on too literally, but it is not saying the
model is completely wrong.
edit: For some reason, I feel the need to make note of the text in my signature here.
[Edited on 10/28/17 by Melgar]
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NEMO-Chemistry
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Regarding if space stretches and where does it come from/go...
Why would it not be like elastic? You pull it and it stretches and let go and it shrinks back, nothing is added or taken away (except force).
Personally i dont see why stretching space would need it to add or subtract anything.
Would answering the questions of the cosmos really give us peace of mind?
Like proving or disproving God, would it help or hinder?
[Edited on 28-10-2017 by NEMO-Chemistry]
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Melgar
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| Quote: Originally posted by NEMO-Chemistry | Regarding if space stretches and where does it come from/go...
Why would it not be like elastic? You pull it and it stretches and let go and it shrinks back, nothing is added or taken away (except force).
Personally i dont see why stretching space would need it to add or subtract anything. |
The usual description is that it's like the surface of a balloon that's being inflated, hence the inflationary model of the universe. However, I
think that it's described as following similar rules as a quantity of gas released into a vacuum. Thus, it's expanding at a changing rate, based on
some initial quantity that we call "dark energy" because we can't see it and don't know what else to call it. So it's not really "coming" from
anywhere, it was here since the beginning, but can't be observed. I don't think we're very close at all to figuring out what "dark energy" is. Dark
matter, we're perhaps a little closer to, though our hypotheses are still largely untestable.
| Quote: | | Would answering the questions of the cosmos really give us peace of mind? |
It's human nature to wonder about things, regardless of their practicality. Like our primate ancestors, we're a curious species, by nature. It would
be a sad universe indeed, if there was nothing we didn't know, and nothing new to learn.
The first step in the process of learning something is admitting that you don't know it already.
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NEMO-Chemistry
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I often here we know more about space than we do about our own planet, particularly the Oceans. Space isnt my thing though, kind of got ruined with
brightest object in the sky here, is the bloody space station!!
Space to me is just one them things likely to drive you insane thinking about it. Although I do belong to the group of 'there must be other life
forms'. Seems to be too many Goldilock zones for life not to exist somewhere else, I doubt we will know though.
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hissingnoise
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| Quote: Originally posted by Melgar |
First of all, I'm glad to see that you're investigating this matter, rather than just writing off everyone that contradicts you as being idiots.
Second, the trouble with astrophysics is that we can only observe the universe from a single point, and thus while we can observe many strange and
interesting phenomena, it is often the case that it is barely within our power as a species to observe them, let alone reproduce them under
experimental conditions. The best we can hope to do is to describe them using a model that people are able to wrap their heads around
|
What'd be nice is 3D astronomical viewing ─ two telescopes in space, a certain great distance apart, focused on the same area of space to produce
pictures/video that may be viewed as in a 3D slide-viewer...?  
And increasing/decreasing their degree of separation should make for 'interesting' effects, don'cha know?  
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Melgar
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| Quote: Originally posted by hissingnoise | What'd be nice is 3D astronomical viewing ─ two telescopes in space, a certain great distance apart, focused on the same area of space to produce
pictures/video that may be viewed as in a 3D slide-viewer...?
And increasing/decreasing their degree of separation should make for 'interesting' effects, don'cha know?
|
For a parsecond there, I didn't know what on Earth you were talking about!
The first step in the process of learning something is admitting that you don't know it already.
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hissingnoise
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Did you mean: what in Space you were talking about?
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phlogiston
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| Quote: Originally posted by NEMO-Chemistry | Regarding if space stretches and where does it come from/go...
Why would it not be like elastic? You pull it and it stretches and let go and it shrinks back, nothing is added or taken away (except force).
Personally i dont see why stretching space would need it to add or subtract anything.
[Edited on 28-10-2017 by NEMO-Chemistry] |
Real-life Elastic materials become thinner as they stretch. Think of the balloon analogy that Melgar mentiones. The material that provided the extra
length did not come out of nowhere.
Ofcourse, it is only an analogy, and I am not sure if it is a useful line of thought to take it this far, but applied to the stretching of space, it
would imply that space has another dimension ('thickness') that can become thinner to allow the 3 spatial dimensions of space that are visible to us
to stretch.
If space is actually made of something, what does 'stretching' do to it?
Thinking of quanta of space being stretched a little further apart doesn't help. The very meaning of 'further apart' depends on the concept of
space/dimensions.
Space that is 'stretched' accommodates more stuff. Therefore, if space is made of something, it seems to me that 'stretching' it implies creating more
of whatever it is that space is (or thinning some unobserved 'thickness' dimension of it)
[Edited on 28-10-2017 by phlogiston]
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Melgar
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| Quote: Originally posted by NEMO-Chemistry | | I often here we know more about space than we do about our own planet, particularly the Oceans. Space isnt my thing though, kind of got ruined with
brightest object in the sky here, is the bloody space station!! |
I'm not really sure where that saying comes from. Perhaps because we spend so much more resources studying space than our oceans? That makes
complete sense though, because there's so much more to learn by studying space. Additionally, I think that quote was first used during the Cold War
when we were trying to beat the Russians in the Space Race. (Not so we could launch nuclear warheads into an orbital that passed directly above
Moscow, of course. That would be MAD.) The thing is, though, most of the oceans are pretty boring. Not much goes on in the abyssal plains, even
though they make up most of the planet's surface. If it wasn't too dark to see there, which it is, it'd look like you were standing in a field of
mud, with nothing but mud to be seen in every direction. All day, every day. With the temperature a constant 4 degrees celcius. (about 38 F)
Hmm... in case anyone missed the joke, parsecs are "parallax seconds" and describe arc-seconds, based on how much stars seem to move when the Earth is
at opposite ends of its orbit. During the early 20th century, that was how astronomers determined how far away different stars are, although it only
works well within our own galaxy. Now, we're sophisticated enough that we can use doppler shifting and other cool tricks to tell how far away things
are, rather than wait six months to take another picture to compare with, and hope nothing moved in the mean time.
| Quote: | | If space is made of something, it seems to me that 'stretching' it implies creating more of whatever it is that space is. |
There's no reason to expect space to follow the same rules as matter and energy. After all, space isn't made of either. Do we know what space is
made of? Sort of. It's made of space-time. That's a bit of a cop-out answer, but if you have a better one, you're welcome to propose an experiment
to test your hypothesis. Until then, we can only use models to describe our observations, and understand that whatever laws we believe the universe
to operate by, if what we observe doesn't follow those laws, then our laws need revising, not the universe.
I think that this is the point aga was making, actually, with the whole broadway musical bit.
The first step in the process of learning something is admitting that you don't know it already.
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wg48
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| Quote: Originally posted by Melgar | | Quote: Originally posted by wg48 | I was also going to suggest you swot up on physics and the scientific principal (the one that requires evidence and testable predictions). But that
apparently has not always worked. Perhaps you need a better BS detector.
“No conspiracy” where did that come from ?. Did some one suggested there is a secret sect of Pi masons who spread unscientific phenomena in
attempt to confuse undergraduates? (humour).
|
First of all, I'm glad to see that you're investigating this matter, rather than just writing off everyone that contradicts you as being idiots.
Second, the trouble with astrophysics is that we can only observe the universe from a single point, and thus while we can observe many strange and
interesting phenomena, it is often the case that it is barely within our power as a species to observe them, let alone reproduce them under
experimental conditions. The best we can hope to do is to describe them using a model that people are able to wrap their heads around. The
"inflation" model of the universe is a model and nothing more. It is a way of describing phenomena to other people. The paper you
referenced describes shortcomings in a common use of this model, and ways in which the model is relied on too literally, but it is not saying the
model is completely wrong.
edit: For some reason, I feel the need to make note of the text in my signature here.
[Edited on 10/28/17 by Melgar] |
In the first sentence of that post of mine was poorly written. I had meant it to mean that even some people whom presumable know a lot of physics like
people who write the curricula of degree courses in physics or books on advanced physics who presumable have done a lot of swotting up believe the
myth. So suggesting swotting up on physics is not necessarily going help dispel the myth.
I was not investigating expanding space. I was trying to understand how the observable universe is 100 billion compared to 13 billion light years. The
calculation I gave previously is wrong I thought I had deleted that section perhaps I forgot to hit the edit button at the end of my edit. I have
failed to understand size problem. The best I can do is: the surface of last scattering was moving away at about 0.9998c (redshift 1001) so its
velocity can not have significantly increased so its present position is double that, double again for a diameter which makes the diameter of
observable universe 52 billion light years (proper distance).
The relativistic redshift between distant objects in the universe is it caused by: either a) Relative motion between the objects or b) Space welling
up between the objects while the objects are stationary” relative to each (the words of a physicist not mine). The more detailed explanation is that
as the light travels between the objects the welling up space stretches the photons which causes the drop in frequency.
Its difficult for me to see how a) and b) as almost equivalents descriptions. This is supposed to be physics not fairy tales for children.
However the root of the welling up of space idea lies deeper in the incorrect belief that the universe expands faster than light. In an infinite and
isotropic (all observers at rest in the locale frame see the universe identically with identical physical laws) universe is not observed to expand
faster than light and hence does not violate SR. I have already explained this so I am repeating myself. It is not pseudosience just SR. Its the sort
stuff I thought they teach on physics courses not fairy tales.
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Melgar
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What you call a "myth", others might call a "model", perhaps? Because regardless, the universe does behave in ways that can't be explained solely by
general relativity. The most commonly used model is referred to as the "Lambda-CDM model", for the constant (lambda) and "CDM" for "cold dark
matter". Here's the Wikipedia page, if you're interested in understanding this model:
https://en.wikipedia.org/wiki/Lambda-CDM_model
The first step in the process of learning something is admitting that you don't know it already.
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Melgar
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The issue is that I'm pretty sure I understand the standard model of the universe, but I'm not sure I understand you. However, the sentence
before your points a, b, and c was the one that I thought best explained it:
| Quote: | | Although this expansion increases the distance between objects that are not under shared gravitational influence, it does not
increase the size of the objects (e.g. galaxies) in space. |
That is, for objects that are not under shared gravitational influence, general relativity apparently doesn't describe the governing laws.
The first step in the process of learning something is admitting that you don't know it already.
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hissingnoise
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Ahem! It's hard to offer anything but the most banal of generalities on a subject large as this, but let's see ─ the ever-accelerating expansion of
the universe, as accepted, is mostly predicated on red-shifted light from distant objects.
The fact that the most distant observable objects display the greatest degree of red-shift is generally taken to mean that their rate of recession is
also greatest.
But the most distant objects are also the most distant in time so that the oldest objects 'appear' to have the highest speeds of recession?
And as we know, when light travels in space, its wavelength increases over time so that there's a distance-dependence on the degree of red-shift
observed and one must wonder how much red-shift is due to recession and how much is due to the distance travelled?
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aga
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Erm, i need to physically be in orbit around Proxima Centauri next weekend and would like to be back a couple of days later.
OK, so Science tells us that by accelerating an object to light speed is the max possible, and it'll take over 4 years each way.
That simply tells us that the trusted "Picking Things up and Throwing Them" method will not work, yet that is the current Best way (albeit with much
stronger arms, i.e. rocketry).
Discovering of the limits of stone-throwing doesn't sound quite so impressive anymore, seeing as 102 years have passed already, and an awful lot of
effort has been focused on verifying the stone-throwing theories instead of anything new.
So, how else can i physically get to our nearest star next weekend ?
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Texium
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Well... actually thanks to relativity and the elasticity of time, if you were hypothetically accelerated to near the speed of light and put on course
to Proxima Centauri, you would feel as if you arrive in much less than 4 years (not sure exactly how long it would be, that would require some math
that's beyond me, but probably much less than a year), and if you were then to come back to Earth immediately after at the same speed, you'd find that
on Earth 8 years have passed even though to you it may have just been a number of days.
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aga
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That solution would not meet the requirement.
Picking me up and throwing me as hard as you can would simply not work, despite how attractive that may sound.
Science already tells us that it would not work, so another way is required.
Time to move on from apes throwing rocks around, although i'm not 100% sure it's time for that yet, insofar as the minds of us apes are concerned.
Edit:
This feels a bit like the Nitric Acid Challenge, where the ONLY methods were nitrate-and-sulphuric or birkland-eyde, as they were best documented, yet
biology was already doing it in peat bogs and that process was already documented on SM.
[Edited on 30-10-2017 by aga]
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Texium
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Location: Salt Lake City
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Mood: PhD candidate!
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I looked up the math for the time dilation effect and turns out it's actually really simple.
https://www.quora.com/Traveling-at-99-9-speed-of-light-insid...
With that, it would take just over two months to reach Proxima Centauri from the frame of reference of someone inside a rocket going 99.9% of the
speed of light. That's about the best you could get, end of story. You won't be able to travel at light speed or faster to get there. Demanding that
people offer you a sci-fi alternative is just trolling.
[Edited on 10-31-2017 by zts16]
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