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What is the universe expanding into?





trousersalive
If the universe is expanding at high speed, what is it expanding into?
greatfire
its expanding into the nothingness that surrounds it, as far as i can tell, although string theory has some other explanation, some thing like our universe is like a slice of bread cant quite remember it fully though
Gagnar The Unruly
Based on my understanding, it's not expanding 'into' anything, per se. Space itself is simply expanding.
Bikerman
trousersalive wrote:
If the universe is expanding at high speed, what is it expanding into?


This comes up a lot and is a hard thing to get straight in your head, I know.

OK, firstly, when we say space is expanding it means something particular. It is not all rushing apart like debris after an explosion - that is frequently used as an analogy and it is incorrect. Spacetime, remember is a 'something', not a 'nothing'. The galaxies are not all rushing away from each other, they are fairly stationary. What is happening is much 'stranger' than that.
The best way I can illustrate it is with a metaphor and like all metaphors it breaks down at some point, but it might help.

Imagine running a long tape measure between here and a far distant galaxy billions of light years away. You would expect the tape to almost immediately snap because the galaxy is, according to red-shift data, hurtling away from us at a good fraction of c (speed of light).
That, however, would not happen, You could site there quite happily with the tape still attached while your telescope told you it must surely have snapped.
How? Well expansion means that space itself is stretching, not the objects within it. The spacetime between distant galaxies stretches, the galaxies themselves are relatively stationary.
When we finally pull the tape measure back in we find the galaxy is still the same distance as before according to the tape. The tape itself, however, since it was stretching through the spacetime, has stretched so that what used to be intervals of metres and kilometres are now (say) now has each metre mark about a kilometre apart if we measure it with another tape.

So, yes, the galaxy is receding from us at very high speed, apparently, but it is actually the space between us that is stretching.
It might seem that there is no difference and so why make the distinction? There is a big difference, though. Matter moving through spacetime cannot exceed c, but there is no rule that spacetime cannot stretch so fast that we might appear to see a distant galaxy receding at speeds greater than c. This is thought to be the case and is one reason we cannot say how big the universe is. All we can say is what is within the Cosmic Light Horizon - that distance which light, had it set-off at the big bang, could have reached us at some point. It is quite possible that a large part of the universe is out of reach because inflation stretched the matter out so fast that not even light could pass between the dustant parts - those parts are out of range and since they cannot interact in any way with us, we can say nothing useful about whether they exist or what they mean.

So to summarise :
without spacetime there is no 'something' 'containing' the universe, there is no time and space for which anything to exist.
Once the universe began, it accelerated apart at a tremendous speed - faster than light could travel. It did and does this by spacetime itself stretching.
It is natural to think that something which is getting bigger must have something in which to grow, but that is because we are earthbound and limited to certain types of geometry and certain 'common sense', assumptions which tell us so. They do not apply when considering extreme physics so we have no useful metaphors and we cannot say 'it is like that' because there is nothing that it is like. It works mathematically but with nothing to compare to, the picture of the tape measure is the best I can do.
Alternatively one other approach sometimes used is the current bun in an oven. The currants are evenly spaced throughout the dough mixture. When the mixture starts to rise in the oven, the currents do not 'move', but they do get further apart because the dough itself stretches.
No metaphor is satisfactory - this is one of those things that works on paper and has to be accepted since it is beyond our experience and imagination to explain in everyday words.

PS - the expansion only happens where gravity is too weak to pull spacetime back. It cannot happen, therefore, near mass, since the gravity of the mass would stop expansion dead. It only happens, therefore, in deep deep deep space. Even out local galaxies around the milky-way are close enough so their gravity stops expansion occurring and the 'local group' of galaxies (as it is known) is not expanding very fast at all - in fact they may one day collapse into each other - and our telescopes agree.
You might ask "what force is driving the expansion" - which is an excellent question. The only answer available at the moment is -Dark Energy.
It could be a property of spacetime itself, we don't know yet.....
Gagnar The Unruly
Say we observe a galaxy that appears to be receding at >c. Would a spacecraft incapable of exceeding c be able to reach it?
Bikerman
Gagnar The Unruly wrote:
Say we observe a galaxy that appears to be receding at >c. Would a spacecraft incapable of exceeding c be able to reach it?

Well the first problem is the killer - how do you observe it? Anything outside the normal light-cone cannot interact with us (or we with it). In fact this is an oversimplification...and I recommend the link at the end to go into more depth...

Secondly, no. A spaceship is massive (it has mass) and therefore would produce sufficient local gravity to ensure that the spacetime it moved through would not expand.

http://www.atlasoftheuniverse.com/redshift.html
trousersalive
So if a body of mass stops spacetime expanding, would a body of sufficient mass cause it to retract?
ocalhoun
Bikerman wrote:


So, yes, the galaxy is receding from us at very high speed, apparently, but it is actually the space between us that is stretching.


Thinking about this theory, the theory that gravity is caused by all objects in the universe constantly increasing in size, and relativity theory at the same time gave me some interesting thoughts...
I won't attempt to articulate them (because I fear that I can't quite do so, as they are not even fully formed thoughts yet), but I figured I might be doing well to share this interesting perspective to view the world from.
Bikerman
trousersalive wrote:
So if a body of mass stops spacetime expanding, would a body of sufficient mass cause it to retract?

In a way that is what a black-hole does..
Bikerman
ocalhoun wrote:
Bikerman wrote:


So, yes, the galaxy is receding from us at very high speed, apparently, but it is actually the space between us that is stretching.


Thinking about this theory, the theory that gravity is caused by all objects in the universe constantly increasing in size, and relativity theory at the same time gave me some interesting thoughts...
I won't attempt to articulate them (because I fear that I can't quite do so, as they are not even fully formed thoughts yet), but I figured I might be doing well to share this interesting perspective to view the world from.

Well, where does the evidence come from for the view that all the objects in the universe are constantly increasing in size? Expansion theory does not specify that - rather the opposite. There are two ways of looking at gravity - as a distortion in spacetime (relativity), or as an exchange of particles - gravitons (particle/quantum theory). Both are caused by/properties of mass so the questions then become
  • a) is mass in some way 'fundamental' or is mass itself a product of some deeper mechanism/effect?
  • b) is mass generally invariant?


The answer to b depends, of course, on relativity - more specifically the relative point of view. From the subject's POV then mass is invariant, whereas from an observer's POV mass varies with velocity according to the normal relativity (Lorentz) factor

The answer to a is no, probably not. Mass is currently thought to be a property produced as particles move through a Higgs field (produced by the hypothetical Higgs Boson). What is perceived as empty space is actually a Higgs field and as particles (some types, not all - photons for example) then the 'drag' produced by the Higgs field is what we perceive as inertia and, therefore, mass.
The new CERN super-collider should be able to detect the Higgs boson if it exists (energies up to 1TeV - trillion electron volts - should be possible and the Higgs is posited to be well within that range).
Tumbleweed
Bikerman wrote:
You might ask "what force is driving the expansion" - which is an excellent question. ....


Even if you do say so yourself Razz

Why is'nt inertia enough ?
Bikerman
Tumbleweed wrote:
Bikerman wrote:
You might ask "what force is driving the expansion" - which is an excellent question. ....


Even if you do say so yourself Razz

Why is'nt inertia enough ?

Well, if the only force were inertia then we would expect expansion to be slowing since no additional force would be present - recent measurements, however, indicate that expansion is actually speeding up..
newbie101
i think its a very big mystery to think about with that small mind...
but one hyposthesis i always think off......

like atoms have electrons revolving,, like wise is this big galaxy and whole universe...

like,, eletrons are nothing in our front like wise may be we this universe is just like atom for anybdy who is --dont know how much big
Rolling Eyes
Bikerman
newbie101 wrote:
i think its a very big mystery to think about with that small mind...
but one hyposthesis i always think off......

like atoms have electrons revolving,, like wise is this big galaxy and whole universe...

like,, eletrons are nothing in our front like wise may be we this universe is just like atom for anybdy who is --dont know how much big
Rolling Eyes

Thanks for that contribution. Please feel free to contribute gibberish anytime
newolder
Bikerman wrote:
trousersalive wrote:
If the universe is expanding at high speed, what is it expanding into?


This comes up a lot and is a hard thing to get straight in your head, I know.

OK, firstly, when we say space is expanding it means something particular. It is not all rushing apart like debris after an explosion - that is frequently used as an analogy and it is incorrect. Spacetime, remember is a 'something', not a 'nothing'. The galaxies are not all rushing away from each other, they are fairly stationary. What is happening is much 'stranger' than that.
...


PS - the expansion only happens where gravity is too weak to pull spacetime back. It cannot happen, therefore, near mass, since the gravity of the mass would stop expansion dead. It only happens, therefore, in deep deep deep space. Even out local galaxies around the milky-way are close enough so their gravity stops expansion occurring and the 'local group' of galaxies (as it is known) is not expanding very fast at all - in fact they may one day collapse into each other - and our telescopes agree.
You might ask "what force is driving the expansion" - which is an excellent question. The only answer available at the moment is -Dark Energy.
It could be a property of spacetime itself, we don't know yet.....


The ontological debates in a four dimensional universe are definitely confusing to most: the bit about the tape-measure is, well, unreasonable. Does it strectch or not? (Of course not, it's made of matter and its Ricci tensor's action on space-time precludes it stretching.) And the explanation that the universe is expanding into nothingness is simply unsustainable. What is 'nothingness'? How can it exist? dE dt, dx dp &c are all >= h-bar... and, if 'nothingness' has 'no time' then when can we expand into it?

The Kaluza-Klein universe, with its extra space dimension (so there's four of them and 1 of time), has been adopted as a truer reflection of reality by the M-theorists on the planet and this extra dimension easily copes with expanding, animated, 3-D holograms like our observable universe.

The implicaions are deep and will be tested by further experiment/observation as this century unfolds. For example, a fifth force (quintessence) is predicted to exist that operates across this 'bulk' 5-D universe (note: it's 11-D actually, when the 6-degrees of freedom for momentum/energy exchange in quantum mechanics are added to the theory properly). Also, 11-D Supergravity theory predicts the existence of supersymmetry in nature: all the quarks, leptons and bosons in the standard model will have supersymmetric partners (spartners) with properties that include sbosons having mass whilst sleptons & squarks are massless.

Interesting times ahead.
newolder
Bikerman wrote:
trousersalive wrote:
If the universe is expanding at high speed, what is it expanding into?


This comes up a lot and is a hard thing to get straight in your head, I know.

OK, firstly, when we say space is expanding it means something particular. It is not all rushing apart like debris after an explosion - that is frequently used as an analogy and it is incorrect. Spacetime, remember is a 'something', not a 'nothing'. The galaxies are not all rushing away from each other, they are fairly stationary. What is happening is much 'stranger' than that.
...


PS - the expansion only happens where gravity is too weak to pull spacetime back. It cannot happen, therefore, near mass, since the gravity of the mass would stop expansion dead. It only happens, therefore, in deep deep deep space. Even out local galaxies around the milky-way are close enough so their gravity stops expansion occurring and the 'local group' of galaxies (as it is known) is not expanding very fast at all - in fact they may one day collapse into each other - and our telescopes agree.
You might ask "what force is driving the expansion" - which is an excellent question. The only answer available at the moment is -Dark Energy.
It could be a property of spacetime itself, we don't know yet.....


The ontological debates in a four dimensional universe are definitely confusing to most: the bit about the tape-measure is, well, unreasonable. Does it stretch or not? (Of course not, it's made of matter and its Ricci tensor's action on space-time precludes it stretching.) And the explanation that the universe is expanding into nothingness is simply unsustainable. What is 'nothingness'? How can it exist? dE dt, dx dp &c are all >= h-bar... and, if 'nothingness' has 'no time' then when can we expand into it?

The Kaluza-Klein universe, with its extra space dimension (so there's four of them and 1 of time), has been adopted as a truer reflection of reality by the M-theorists on the planet and this extra dimension easily copes with expanding, animated, 3-D holograms like our observable universe.

The implications are deep and will be tested by further experiment/observation as this century unfolds. For example, a fifth force (quintessence) is predicted to exist that operates across this 'bulk' 5-D universe (note: it's 11-D actually, when the 6-degrees of freedom for momentum/energy exchange in quantum mechanics are added to the theory properly). Also, 11-D Supergravity theory predicts the existence of supersymmetry in nature: all the quarks, leptons and bosons in the standard model will have supersymmetric partners (spartners) with properties that include sbosons having mass whilst sleptons & squarks are massless.

Interesting times ahead.

__________________________

This is the (accidental) 2nd copy of above. The 'edit' button says 'edit/delete' on its tool-tip text but there's no delete.

Could a moderator oblige, please? ed.
Bikerman
newolder wrote:
The ontological debates in a four dimensional universe are definitely confusing to most: the bit about the tape-measure is, well, unreasonable. Does it stretch or not? (Of course not, it's made of matter and its Ricci tensor's action on space-time precludes it stretching.) And the explanation that the universe is expanding into nothingness is simply unsustainable. What is 'nothingness'? How can it exist? dE dt, dx dp &c are all >= h-bar... and, if 'nothingness' has 'no time' then when can we expand into it?
Yes, fair points, both. The analogy did carry a health warning Smile I was simply trying to get across the notion that deep space is where expansion occurs and it is not a result of things moving through spacetime, rather spacetime itself 'stretching'. I've tried to find a better analogy or metaphor but failed miserably up to now Sad
Quote:

The Kaluza-Klein universe, with its extra space dimension (so there's four of them and 1 of time), has been adopted as a truer reflection of reality by the M-theorists on the planet and this extra dimension easily copes with expanding, animated, 3-D holograms like our observable universe.
Yes, I finished the first section on KK space in Penrose a while ago (ch15) and the next encounter is several hundred pages ahead (ch.31). Maybe when I get to Ch.31 I'll understand well enough to be able to describe better. Smile
Quote:

The implications are deep and will be tested by further experiment/observation as this century unfolds. For example, a fifth force (quintessence) is predicted to exist that operates across this 'bulk' 5-D universe (note: it's 11-D actually, when the 6-degrees of freedom for momentum/energy exchange in quantum mechanics are added to the theory properly).

Would Quintessence be the force which is currently known as either Cosmological constant or Vacuum point energy (or, more generically as Dark Energy)? In short the anti-gravity 'expansive' force required to explain the acceleration ?
Quote:
Also, 11-D Supergravity theory predicts the existence of supersymmetry in nature: all the quarks, leptons and bosons in the standard model will have supersymmetric partners (spartners) with properties that include sbosons having mass whilst sleptons & squarks are massless.

Interesting times ahead.

Yes indeed....Just as I start to get towards a point where I can make some sense out of current theory, it looks like current theory is headed off again - this time to quintessence, supersymmetry and super-gravity.....If I pay the conductor an extra penny do you think he might hold the Bus at the current stop for a bit longer Smile
xC
newolder
Theoretical ideas, if they are to be useful (and without the cost of even a penny!), must describe everything as well as theory hitherto and then attempt to simplify. The universe wasn't observed to be accelerating in its expansion 'til the 1998 distant supernovae events and things moved quickly thereafter. This is probably why the ideas haven't made it to public consciousness yet, but we are working on this as best we can.

Here's an AstronomyToday article* with some of Steinhardt's thoughts included - another fine read for when the reader has time... Smile

Penrose maintains that 10-D is sufficient to describe all there is and the cosmological constant is seen there not as Einstein's greatest blunder because it isn't even a blunder! The equivalence between it (lambda), Dark Energy and quintessence will emerge in future discussions, i guess...

I read a technical article on quintessence some time ago that i can't point my browser to at the moment**.

Happy reading.

* http://www.astronomytoday.com/cosmology/quintessence.html

** Here it is: Fifth force from fifth dimension:: http://citeseer.ist.psu.edu/cache/papers/cs/4235/http:zSzzSzastro.uwaterloo.cazSz~wessonzSz5force.pdf/fifth-force-from-fifth.pdf
Bikerman
newolder wrote:

Happy reading.

* http://www.astronomytoday.com/cosmology/quintessence.html

** Here it is: Fifth force from fifth dimension:: http://citeseer.ist.psu.edu/cache/papers/cs/4235/http:zSzzSzastro.uwaterloo.cazSz~wessonzSz5force.pdf/fifth-force-from-fifth.pdf


Nice link - very interesting - I'm currently on page 7 and still following the math OK...
Ahh....just started P8.....going to have to concentrate to read the rest, it's getting tougher Smile
newolder
'ello, again...

I'm trying to reference the above-linked Mashhoon et al work properly but i can't seem to find a date-stamp anyhwere. Can you, please, Chris? Or anyone else?

Cheers again.
Bikerman
newolder wrote:
'ello, again...

I'm trying to reference the above-linked Mashhoon et al work properly but i can't seem to find a date-stamp anyhwere. Can you, please, Chris? Or anyone else?

Cheers again.


Hmm...this may help..the Bibtex on the above is :
author = {{Wesson}, P.~S. and {Mashhoon}, B. and {Liu}, H. and {Sajko}, W.~N.},
title = "{Fifth force from fifth dimension}",
journal = {Physics Letters B},
year = 1999,
month = jun,
volume = 456,
pages = {34-37},
adsurl = {http://adsabs.harvard.edu/abs/1999PhLB..456...34W},
adsnote = {Provided by the Smithsonian/NASA Astrophysics Data System}
newolder
Smile

Is there a url to that bibtex info too, please? I searched the 'document properties' in adobe reader but found nothing...

I'm thinking a lot about the physical interpretation of the fifth dimension described by Mashhoon et al and keep coming to the conclusion that our 10-brane is embedded(?) in a dimension that we would recognise as 'massy' but i don't seem to have the language skills to write it down properly, yet... The first few (50-ish) words are here* but, hopefully, it'll expand as time goes by. The implied supersymmetry is striking, i'm sure you'll agree?

Thanks again. ed.

* http://newolder.netfirms.com/quintessence,%20supersymmetry%20and%20tachyons%20off%20the%20mathematical%20page.htm
Bikerman
newolder wrote:
Smile

Is there a url to that bibtex info too, please? I searched the 'document properties' in adobe reader but found nothing...

I'm thinking a lot about the physical interpretation of the fifth dimension described by Mashhoon et al and keep coming to the conclusion that our 10-brane is embedded(?) in a dimension that we would recognise as 'massy' but i don't seem to have the language skills to write it down properly, yet... The first few (50-ish) words are here* but, hopefully, it'll expand as time goes by. The implied supersymmetry is striking, i'm sure you'll agree?

Thanks again. ed.

* http://newolder.netfirms.com/quintessence,%20supersymmetry%20and%20tachyons%20off%20the%20mathematical%20page.htm


No problemo,
Bibtex url here:
http://adsabs.harvard.edu/cgi-bin/nph-bib_query?bibcode=1999PhLB..456...34W&data_type=BIBTEX&db_key=PHY&nocookieset=1
Host System containing Bibtex reference here (Harvard Uni)
http://adsabs.harvard.edu/abs/1999PhLB..456...34W
CiteBase entry here:
http://citeseer.ist.psu.edu/238355.html

It sounds deep. I think I understand you to be saying something along the lines of the 11-d supergravity model can look like 10-d super string theory. This could happen, maybe, if we start with 2-branes in 11-d super gravity and then 'Roll up' one dimension to leave the 2-brane encircling it looks like 1-d string? err, maybe Smile.....it's way beyond my current level and I'm probably wildly off the mark....

The following might or might not help...
1. Paper I came across which seems apposite: http://www.iop.org/EJ/article/1475-7516/2005/09/002/jcap5_09_002.pdf

2. Discussion on PhysicsWeb on adjacent territory
http://www.physicsforums.com/archive/index.php/t-42239.html
newolder
It's good to read others (e.g. the 2004 topic at physicsforums) are keeping pace too. Smile The English language translations there are probably more mathematically correct than mine but then again, i'm just a physicist. Cool

article at your first link:: http://arxiv.org/PS_cache/hep-th/pdf/0507/0507239v2.pdf

Our D-brane (10-dimensional, Dirichlet-geometry) is possibly a reflection of another. The reflection occurs on a hyperplane that is tangential (asymptotically flat and Euclid suffices) to a warped (at best) or spherical or toroidal donut (at most perfect) 5-dimensional manifold that is large and resembles mass better than any other English word.

It gets weirder the deeper one digs: time to surface elsewhen, methinks.

Cheers again, ed. Very Happy

P.S. Have you tried the "Physics and mathematics" tab at the Royal Society's tv-web? The First 100 minutes or so are Dr Tara Shears' excellent talk on the LHC@CERN:: http://tv.royalsoc.ac.uk/dpx_live/dpx.php?dpxuser=dpx_v12
Ennex
It's...expanding into more space....that's all you can say lol....whether it's going to collapse in on itself is another story (lol read up on Stephen Hawking)...but yeah, it's essentially just creating more nothingness that we have now...whether planets and suns will be created we'll find out in a few hundred million/billion years...but I doubt we'll ever know then Razz
newolder
Ennex wrote:
It's...expanding into more space....that's all you can say lol....whether it's going to collapse in on itself is another story (lol read up on Stephen Hawking)...but yeah, it's essentially just creating more nothingness that we have now...whether planets and suns will be created we'll find out in a few hundred million/billion years...but I doubt we'll ever know then Razz


O dear, ennex, there's many ways to demonstrate that you are confused but, happily, the confusion is easily resolved these days by simply reading around the subject...

Start with Euclid and progress to Reimann by the usual route. Pick-up on Hamilton as you go and then you'll be ready to add Newton/Liebnitz, Einstein/Minkowski, Planck, Heisenberg, Pauli, Dirac et al, Feynman, Veneziano, Witten, Steinhardt & Turok and then you'll be in a position to read Penrose, "The Road to Reality", 2004, OUP.

It's demonstrably so and it's not all absurd (as your current view suggests). Smile
dbhai
Today it is mystery but someday we will be able to find out where it is expanding and if there is a limit to it or not and will it ever begin shrinking too.
Tumbleweed
Bikerman wrote:
Tumbleweed wrote:
Bikerman wrote:
You might ask "what force is driving the expansion" - which is an excellent question. ....


Even if you do say so yourself Razz

Why is'nt inertia enough ?

Well, if the only force were inertia then we would expect expansion to be slowing since no additional force would be present - recent measurements, however, indicate that expansion is actually speeding up..


I dont quite get whats to stop the initial BB's inertia, why would we expect things to slow down when theres nothing to slow it ? some kind of after the act drag ?
Gagnar The Unruly
Gravity is the answer to your question.
GSIS
Idea Perhaps it's expanding into the multiverse?

As each chance encounter, or event, occurs and each of the possible outcomes creates a new universe the multiverse expands to contain all of those possible universes. The number of universes will never be infinite - just an incomprehensibly huge number - so the multiverse will also never be infinite and nor will the dimensions it occupies.

Could this be a Eureka moment? I think not - but I did just get out of the bath. Wink
newolder
GSIS wrote:
... The number of universes will never be infinite...


Correct. The number required to describe the configuration space for energy is very, very much greater than Cantor's Aleph-null or plain-old infinity. Nowadays, the number is commonly referred to as C, the cardinality of the set of real numbers, and is 2^Aleph-null in size. Cool
EanofAthenasPrime
Bikerman wrote:
newbie101 wrote:
i think its a very big mystery to think about with that small mind...
but one hyposthesis i always think off......

like atoms have electrons revolving,, like wise is this big galaxy and whole universe...

like,, eletrons are nothing in our front like wise may be we this universe is just like atom for anybdy who is --dont know how much big
Rolling Eyes

Thanks for that contribution. Please feel free to contribute gibberish anytime


lol sum1s been watchin 2 much MIB Cool
breebree
I read somewhere that there are certain circumstances in which light can exceed c but what would happen if an object were to exceed c?
Indi
breebree wrote:
I read somewhere that there are certain circumstances in which light can exceed c but what would happen if an object were to exceed c?

The short answer is that light can never exceed c.

The long answer is that there is more than one "speed of light", and some of those speeds can be less than, or even exceed, c. But still, the best "practical" speed - the signal velocity - is always c, never faster or slower.

But no object - assuming "object" means particle with mass - can be accelerated to the point where it even reaches c, let alone exceeds it.

(And to make things even more fun, because all matter is really waves, all matter has multiple speeds, too. The "practical" speed, the group velocity, can never reach c... however... the phase velocity of matter is usually far more than c! However, that speed has no practical relevance.)
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