the expanding universe.

[peter]

If I buy the best telescope that money can buy - one in fact so good that it can see right to the point at which the big bang occurs [ie the light from this distance has taken the entire time that the universe has been in existance just to reach us], then this is as far as it will ever [or any other telescope] will be able to see. This is 'the Observable Universe'. Beyond this distance [what is this distance by the way] there exists the Non-Observable Universe, non-observable because it's existence is at a distance beyond the point where the light could travell to us in the time that the universe has existed and thus, in order to see it you would be seeing things that existed before the big bang [not happening.]

But anyways the 'red shift' we see irrespective of where we point our telescopes can only be accounted for if we assume the Universe to be expanding. But there is no central point from which the expansion is occuring; in fact there is no central point in the universe at all - every point in the Universe is at the center and every point is expanding away from every other point; in fact it is the very space of the Universe itself that is expanding not just 'the leading edge' as it were. In fact there is no 'leading edge'.

But hold on. If the Universe is expanding, must it not be expanding into something. If one cannot say what the Universe is expanding into, does it not become meaningless to say it is expanding at all. Surely ther must be a 'relativity' even in the expansion of the Universe, such that if no 'frame of reference' in respect of this expansion can be established - then it cannot be said to be happening at all and really all we are doing is looking at the pretty colors.

[Vraith]

But hold on. If the Universe is expanding, must it not be expanding into something. If one cannot say what the Universe is expanding into, does it not become meaningless to say it is expanding at all. Surely ther must be a 'relativity' even in the expansion of the Universe, such that if no 'frame of reference' in respect of this expansion can be established - then it cannot be said to be happening at all and really all we are doing is looking at the pretty colors.

Yea...what IS it [if anything] it is expanding into?
I don't know. I'm not sure anyone really does.
I have an idea I like, in mostly a metaphorical/surreal way since I don't think it's necessarily so, nor testable even if true...since it seems like in our universe even "empty space" is a fabric/has attributes, what we are expanding into is "space" that really IS "empty." [[somewhat like seed-crystals work...but don't look at that mechanism too closely, cuz then my metaphor falls apart...look at it "magically " ]

The frame of reference, though...that's different, I think [though part of our brain problem of comprehending what/if we're growing into...]
Particular frames limit what you can, even in theory, know...but it doesn't follow that you can't know ANYTHING just because you can't know EVERYTHING. Just because we don't know exactly where/what the Milky Way and Andromeda are getting themselves "into," the relationship between is still real. [I'm pretty sure I saw somewhere us and Andromeda are actually on a collision course... ]
In addition, as I'm sure I've said elsewhere, we humans can change our frame of reference. And not just in one way, in many ways. We can do it literally. We can also do it conceptually/logically/imaginatively. We can even hold in our minds simultaneously more than one frame...frames that may well be inconsistent with each other...and from that clash, discover or create that which is, sometimes literally, impossible/unknowable by any of them in isolation.

[SerScot]

Right, the Universe doesn't "expand" into anything. It is space itself that is expanding. There is no border we can reach were we see the universal expansion take place. I believe this is largely because the Universe exists in more than three dimensions.

The confusion arises because most people imagine the "Big Bang" as an expolosion of stuff into space. It was not. The "Big Bang" was an explosion of space itself. Space is the medium in which we exist. Per Einstein it has substance that can bend and flex. Gravity is a localized incident of space warped by the presense of a large amount of matter. It creates a gravity well.



What if matter is just a bit of space that has gotten all knotted up? Those knotts further warp space and bend towards each other clumping together creating the large globs of matter we have in the visible universe.

[Hashi Lebwohl]

^ What SerScot said. Matter is highly compressed spacetime--you are made of exactly the same stuff as the space in between you and your computer.

The farther away something is the faster it is moving away from us, exceeding even the speed of light (albeit not in an absolute sense). If you walk in one direction at 1 kph and I walk in exactly the opposite direction at 1 kph then we are moving away from each other at a rate of 2 kph *but* we are walking away from each other on a surface which is expanding then our relative velocity of moving away from each other is greater than 2kph, depending upon the rate of expansion of the surface.

This also explains why space is dark--all the energy from early in the universe has red-shifted below our eyes' ability to detect it. If we go far enough into the past, the universe would be fully lit in every direction all the time, which would probably look odd.

[wayfriend]

One thing I think is neat.

If you have an explosion in which particles are dispersed in all directions, and the particles are all ejected at varying speeds, from zero to a maximum, then you can choose any particle, and from that particle's point of view, all other particles seem to be flying away from it, in all directions, and at varying speeds.

Everywhere in the universe appears to be the center of the big bang.

[Hashi Lebwohl]

Which proves that I am, in truth, the center of the universe.

of course.....so are you.....

[Fist and Faith]

A search doesn't find it. Maybe I was saying this recently somewhere else. A Wrinkle In Time had me thinking along the lines of what Vraith said. They went to a two-dimensional reality. It's been years, but, iirc, she was thinking that she wanted to breath. Almost in a panic because she couldn't. But, being 2D, she didn't need to. My point being that that reality did not have a third physical dimension. And, even if it's empty of everything, our empty space has something: three physical dimensions.

Not sure about that "every point is the center of the universe" stuff. The explosion analogy suggests that, if there is a super-observer, it would see the actual point of the explosion, just as we know where the grenade went off. (I'm not ruling out the possibility that Hashi is the center of the universe, though!)

[peter]

Some seriously thought provoking stuff there. I love the 'mental somersaults that V's space expanding into 'empty space' [the idea that it is space itself expanding and not the Universe [as evisaged from 'outside'] itself doing so. Super concentrated little knots of space tied confusedly into the matter we see around us - I love it! And a Universe where we could still see the light prior to it's falling beow the visible end of the specrum - that I want to see!

Two things - when I was thinking out the observable vs the unobservable bit of the original post, this 'distance' beyond which we cannot see due to the very speed that light travels and the time constraints of the universes actual existance, it seemed to me somewhat similar [in concept, if not in physics] as that of a sort of 'event horizon' of distance. Have we any reason to believe that things beyond this 'event horizon' are the same as inside it. Is there just 'universe without end' on the other side, are furthur 'event horizons' encountered due to differing physical parameters as you go yet further 'out'. Are we just scratching about like chickens in our own back yard totally failing to see the bigger picture of the Universe at Large.

Secondly - I'm not sure I was usin the term 'frame of reference' in the same manner as V. was in his post. For me a frame of reference is a thing that allows you to make a judgement pertaining to something - say size, or speed, that without it you could not. eg If a new building were built in the dessert, a 'skyscraper' that I was viewing from a distance on it's own, I could make no guess as to it's height [assuming it had no external features that allowed me to]. But if on the otherhand, it is constructed right next to a scale model of the Eiffel Tower, then I immediately can use this as 'a frame of reference' upon which to base my guestimate of the new buildings height. Is there meaning to the term beyond this when it is used in a physical context that the second part of V.s post is drawing on.

[Vraith]

Two things - when I was thinking out the observable vs the unobservable bit of the original post, this 'distance' beyond which we cannot see due to the very speed that light travels and the time constraints of the universes actual existance, it seemed to me somewhat similar [in concept, if not in physics] as that of a sort of 'event horizon' of distance. Have we any reason to believe that things beyond this 'event horizon' are the same as inside it. Is there just 'universe without end' on the other side, are furthur 'event horizons' encountered due to differing physical parameters as you go yet further 'out'. Are we just scratching about like chickens in our own back yard totally failing to see the bigger picture of the Universe at Large.

Secondly - I'm not sure I was usin the term 'frame of reference' in the same manner as V. was in his post. For me a frame of reference is a thing that allows you to make a judgement pertaining to something - say size, or speed, that without it you could not. eg If a new building were built in the dessert, a 'skyscraper' that I was viewing from a distance on it's own, I could make no guess as to it's height [assuming it had no external features that allowed me to]. But if on the otherhand, it is constructed right next to a scale model of the Eiffel Tower, then I immediately can use this as 'a frame of reference' upon which to base my guestimate of the new buildings height. Is there meaning to the term beyond this when it is used in a physical context that the second part of V.s post is drawing on.

On the first...the first word I ever heard for what you are talking about in the "event horizon" was "light bubble."...13billion light years in every direction , and much like being inside an expanding event horizon.
But, because space itself if expanding, everywhere, the theoretically "observable universe" is nearly 100billion lightyears diameter [I think that's the correct number]...and it's very likely that that "volume" is all pretty much the same as it is around here. After that...no one knows...that's where the "what [if anything] we expand into" "border" "exists."

No, your frame of reference is basically the same as mine. You just sliced off a little piece of it is all. You're just using a specific tool in the general box...your Eiffel model only works the way you say because you've already framed, measured, and labeled it...so you can now use it as a reference. [[you don't need it though, unless there is a specific reason you need to know how many Eiffel's your building is.]]
One could say that everything that can be known...by anyone/thing, not just us...is made up of frames of references and analogies. [and analogies are just a particular kind of frame].

[peter]

Yes - I did think after posting I hadn't really nailed it. A 'frame of reference' in the 'Einstein' sense was all about your particular 'viewing position' *relative* to anothers - somewhat different to my example above.

[Zarathustra]

Don't forget that inflation expanded the universe faster than the speed of light, so in terms of observable universe, there are always going to be some beyond what we can see. And the farther out we look, the faster things are receding away, so that's another kind of "event horizon" too. Once we look far enough that things are moving at the speed of light, we can't look any farther.

Search on Youtube for 3-d map of the universe. I had no idea how much NASA has mapped. There's a short cgi "movie" that flies you through what we have mapped, with each dot representing one galaxy. It's astonishing.

(edit: this one)

[Fist and Faith]

So how does this work... If we observe something that is 15 billion light-years away, it's what it looked like 15 billion years ago. But if the Big Bang was 15 billion years ago, there were no galaxies, or even stars. Such things didn't come about until much later. So how can we see a galaxy or star from 15 billion light-years away?

Also, whatever we see 15 bly away is now muuuuuuuch farther away. We've been moving farther and farther apart since the light left the source. How far apart are we now? And doesn't it meant the universe is at least that old?

[Vraith]

And the farther out we look, the faster things are receding away, so that's another kind of "event horizon" too. Once we look far enough that things are moving at the speed of light, we can't look any farther.

Yea, that's part of what I was talking about.
One odd [or at least it seems counterintuitive at first] effect of that is, barring some faster-than-light observation and movement, the "observable universe" becomes "smaller" in some ways. Not "really" smaller...but because the space itself is inflating, the accessible information/effects available for observation is "shrinking"...The AMOUNT of "stuff" beyond that "can't look any further" point you mention is increasing. Some star, or whatever, is RIGHT NOW, in an [theoretically, if not practically] observable "place."...
And RIGHT NOW it no longer is...it is "gone," and will never be observable again. [it's "past" from our point will be...but not it's future."]
[[heh, in another thread folk were talking about a Brin series...this issue comes up in that on a somewhat shorter scale].

Yet...that might not be totally true...at least not as the way I've said it...have to say it, perhaps, because of how communicating [and relativity, and frames] works...implies.

[peter]

Fantastic link Z. - and one that really drives home the point that Professor John Gribben made [in a small book of his I read] that at the 'inside galaxy level' space is a pretty empty place, but viewed fron the point of whole galaxies it's literally crammed to the gills with the things. There's hardly enough room to breath!

I'm tring to get my head around this 'bigger than the light could travel in 15 billion years thing'. Does that demand that the expansion has been [or is] actually faster than the speed of light - it has to, doesn't it?

[edit; Short term memory situation Z - just re looked at your post re the above. I'm guessing Einstein would not have been happy with this paticular idea!]

[Hashi Lebwohl]

The expansion is effectively faster than c, yes. As I noted before, if you are walking west at 1 kph and I am walking east at 1 kph then our separation velocity is 2 kph.
Now....suppose there is an observer sitting on your shoulder and, as far as they can tell, the speed of light is 1.5 kph. That observer would be able to calculate my velocity as 2 kph moving away from him, which would seem to violate his speed of light limitation unless he takes into account the fact that he is also moving away from me.

To get a little stranger, now suppose that we are walking away from each other on a stretchable surface which is being pulled outward in all directions. Not only are we still moving away from each other at 2 kph but because what we are walking on is being stretched our effective rate of separation is greater than 2 kph. If we wanted to turn around and move towards each other not only would we have to cover the distance we walked the stretchy surface would still be expanding in the meantime. We will never meet unless our rate of moving towards each other is greater than the rate at which the stretchy surface is being stretched.

The observable universe goes back only so far--nearly 13 billion years or so--because beyond that the background emissions have red-shifted so far that the energy is barely detectable even to radio telescopes which can see farther than visible light ones.

My problem with Big Bang is that it doesn't make sense that there should have been a pre-existing condition at a single point in which everything which would become matter and energy suddenly exploded to create everything. Why did it explode when it did? Wouldn't there have to be a cause for that explosion but that would mean some sort of imbalance occurred in the primordial spot? Why didn't it explode before it did (of course, there wasn't a such a thing as 'time' then so there wouldn't have been a 'before' or an 'after')?
These questions are why I like the membrane hypothesis. Membranes allow for 'before the Big Bang' and that the universe as we know it is the result of two or more membranes colliding; the current expansion is because they are still colliding. At some point the membranes may be through colliding and start drifting apart again, which we would observe as a shrinking universe.

[wayfriend]

The expansion is effectively faster than c, yes. As I noted before, if you are walking west at 1 kph and I am walking east at 1 kph then our separation velocity is 2 kph.

... only for very small velocities! As the velocity approaches c, this changes. If you are walking east at c, and I am walking east at c, our relative velocity is ... c!

According to Special Relativity, the relative velocity is not a + b, it is (a+b)/(1+ab/c²).

In short, you can't have relative speeds faster than the speed of light. At least, not this way.

The implications of this is that, if the Big Bang explosion was limited to the speed of light, there cannot be ANYTHING so far away as light hasn't had time to reach us.

If there IS something so far away that light hasn't had enough time since the Big Bang to reach us, it must have been travelling faster than the speed of light at some point. Probably during the initial instants of creation, when physical laws themselves were in flux.

[Zarathustra]

If there IS something so far away that light hasn't had enough time since the Big Bang to reach us, it must have been travelling faster than the speed of light at some point. Probably during the initial instants of creation, when physical laws themselves were in flux.

Yes, inflation happened very early on in the beginning of the universe. And yes, it expanded the universe faster than the speed of light. But no, the physical laws weren't in flux. If the physical laws were in flux, then we'd be altering the laws of universe with our particle accelerators, which reproduce the conditions at (or close to) the beginning of the universe. Extreme conditions are still within natural laws.

It doesn't violate relativity for space itself to expand faster than c. C is only a speed limit for things traveling within space itself, things that have mass. Space doesn't have mass.

That's also why you can effectively go faster than c by going into a wormhole. You circumvent all the space in between. It's a literal loophole in the universe's ultimate speed limit.

[Hashi Lebwohl]

According to Special Relativity, the relative velocity is not a + b, it is (a+b)/(1+ab/c²).

In short, you can't have relative speeds faster than the speed of light. At least, not this way.

The implications of this is that, if the Big Bang explosion was limited to the speed of light, there cannot be ANYTHING so far away as light hasn't had time to reach us.

If there IS something so far away that light hasn't had enough time since the Big Bang to reach us, it must have been travelling faster than the speed of light at some point. Probably during the initial instants of creation, when physical laws themselves were in flux.

hrm.....let me double-check but I think you are correct. I was pretty certain that it is possible to detect object which appear to be receding at velocities which exceed c but I'll have to double-check that, as well.

I don't know if I would say "in flux" but the laws of physics in the very early universe (before 5 seconds) were a little different than they are now--quantum effects were taking place at the macro level, which causes all sorts of weirdness.

[Zarathustra]

True, but quantum effects are part of natural laws. Also, there wouldn't have been enough time for atoms to have formed, so nothing like chemistry would have happened yet. Things were in flux, certainly but it was still all governed by physics ... which is how we know what it was like. If the laws themselves were in flux, then we wouldn't have a clue what the conditions were like.

[wayfriend]

This popped up today.

Detection of primordial gravitational waves announced

It's now clear that we've detected the first direct evidence of the inflationary phase of the Big Bang, in which the Universe expanded rapidly in size. [...] Primordial gravitational waves remain one of the outstanding untested hypotheses of inflation, the most popular model that explains the incredible uniformity of the CMB. According to inflationary theory, the Universe expanded very rapidly in the first fraction of a second, filling the cosmos with gravitational ripples. While inflation so far seems to explain a lot about the Universe, we have no direct evidence for it.

BTW, what I was referring to about physical laws.

However, inflationary cosmology cannot be the ultimate theory of the Universe. If one projects the Universe backward in time, it gets so hot and dense that the laws of physics on which inflation is based (classical general relativity) break down. In the so-called Planck era, lasting up to one Planck second (10^-43 s) after the big bang, the force of gravity would have reached values comparable to the other fundamental forces. In this regime, quantum gravity effects would have been important, creating conditions that go beyond the conventional understanding of space and time. [link]

I am not sure if exceeding the speed of light would have been [more] possible in the Planck era. I suspect it would.

However, today's article just happens to mention something that I had not heard of:

The earliest moments of the Universe's history are hidden from us: the Universe was opaque to all forms of light from the Big Bang until about 380,000 years afterward. However, we can still reconstruct much of what happened in the interim, thanks to radiation emitted when the cosmos became transparent. That light (the cosmic microwave background) encodes much of what happened before it formed, much as earthquakes reveal information about what's going on deep beneath the surface.