How we know the Universe has not existed forever

You will one day and then in 30 or so years you will get the Noble Prize and a free parking spot at UCB or whatever Uni you are at.

I like that, "Noble Prize." LOL

It won't be "Noble Gas Prize."

Satts, et al,

If the "observable universe" is in fact expanding, or if in fact it only looks that way, we are, forced in either case to look for masses beyond the limits of the observable universe.

One question seems to arise. What density of space would be required to either continually accelerate the masses involved at the edge of our observable universe --OR-- To provide the force of gravity (in this case spacetime) which is acting on the red shifted light that we are using to make these deductions?

Satts, I just had another nasty thought. We do not know if our observable universe is actually expanding(decreasing in density), or if it just looks that way, or if the spacetime beyond our observable universe is collapsing (increasing in density). Either alternative, and there may be others, is messing up the red shift something awful.

Albert certainly did leave a legacy with a vengance Best, M

It is possible that the universe is finite (i.e., began).
It is possible that the universe is infinite (i.e., neither began or ended).
It is possible we do not know how to determine what is or is not possible.

We think that what we have observed and what we have inferred from what we have observed, implies that the universe is probably finite.

Nonetheless, it seems to some of us that it is possible that the universe is infinite.

It is also possible none of us have a clue what is and is not possible.

So I agree with ebrown. Without any data whatsoever to imply that the universe is infinite, I bet it is probably finite.

ANALOGY

It is possible that God exists.
It is possible that God does not exist.
It is possible that it is not possible for us to know whether it is possible for God to exist or not exist.

Wait a minute! What is God? Can you define it?
If you cannot define it, what makes you think you can know whether it exists or not?

I solve this problem this way. I define the universe and God to be one and the same thing. Then by definition God exists if the universe exists. I assume the universe exists.

Wait a minute! What is the universe? Can you define it?
If you cannot define it, what makes you think you can know whether it exists as an infinite or finite entity?

I solve the problem this way. I define the universe to be one and the same thing as that which has been, is, and will be observed, and that is inferred from what has been, is, and will be observed.

I ASSUME
=>we cannot observe anything not of the universe.
=>anything not of the universe does not exist.
=>that which has been and is observed and is implied by what is observed, exists.
=>the universe is probably infinite if and only if some observations of it imply it is infinite.
=>thus far no such observations exist.
=>it is possible that no such observations will ever exist.

PROBABLY
The universe is finite.

POSSIBLY, MAY BE
We can know that something not shown to be probable is possible.
We cannot know that something not shown to be probable is possible.

CONCLUSION
For me, the interesting questions are those regarding our observations and our inferences from those observations. Speculating on the possible has little or no utility to the increase of our knowledge, unless such speculation leads to speculation on what is probable.

Is it agreed probable that inferring, merely from its possibility alone, the probability of a particular possible thing, is not possible? If so, why continue to discuss it?

You must be asking about the critical density at which a galaxy (in the universe) barely escapes velocity without superfluous energy. It is

(3HH)/(8(pi)G)

where H is Hubble's constant, G is Newton's constant of gravitation.
(.. A Mathematical Supploement Note 2 of "The First Three Minutes" by Steven Weinberg.)


One of the current problems is that the (observable) universe not only appears to be expanding but that its rate seems to be accelerating.

one might note that, if matter is 'happening' from the interstitial nothingness between the atoms of our known universe, constantly, this would make the observed universe 'appear' to be expanding (just thought i would mention it).

and ican; "we" don't think the universe is probably finite, "you" do;
i (the royal we) know that it makes most sense for that which defines the concept "everything that there is" is most probably 'infinite'.

~I think I disagree. Much reguarding the beginning of the Universe, is untested, perhaps untestable. Your test;~ There is no other rational way to explained what is observed. ~will always be subject the opinion of what is rational. Why are you eagar to nail down a beginning for the Universe? Neil~

Neil

You didn't address your question to anyone.

Who were you asking.

Frankly, I cannot wait to hear the answer.

Satts, That's the problem;
"The Universe not only appears to be expanding, but its rate seems to be accellerating."


We don't know if the Universe is actually expanding. Meaning that the average distance, measured in meters, (or some derivation thereof) between galaxies is increasing--or

We don't know if it merely looks like it is expanding, due to the nature of light interacting with spacetime--or

If something massive beyond the microwave background is affecting our observable space time--or

Or if this portion of the cosmos is collapsing thus resulting in more spacetime between massive objects in our observable universe.

All four scenarios could probably result in light being "red shifted" as we observe it.

If it is actually expanding into a volume that didn't exist until the Big Bang got there then the Big Banger and the Creationists would have some common ground perchance to build a dialogue upon.

If it only "looks like" it's expanding then the Steady Staters and the Buddists have some common ground, perchance to begin understanding.

So I at this point still take umbrage at the title of this thread.
"How do we KNOW the Universe is expanding."
Somehow I don't think we do. But I would like to

Bogowo, Sorry I miissed it,

Your observation would count as the fifth hypothesis in my last post.

I have even run across the calculations that some PHD has done that show the amount of matter that would have to be created in our observable universe in order to make it square with observations (which IMO) may be misinterpreted.

akaMechsmith..
One thing should be clear:
If one says the universe is expanding, one means the expansion of the scale of the universe not the actual distance inside it. But it is like a transition of 1:1000000 map becoming to a 1:10000 map and then 1:1000 map..
The map expands but the distance does not.

Ican, If you subtract the Big Bang and add a Cosmos to Our Observable Universe then I suspect that the observed red shift may fit a little better.

This view has the advantage of not requiring any particularly strange physics.

Therefore it's probably infinite except for OOU which is finite by definition. We won't discuss eternity yet. We've got some time left

Satts, Crossed posts,

I can't quite visualize that! If the universe was once infinitely small and has progressively become larger over the last thirteen billion years how does that not change the absolute distance between galaxies?

akaMacksmith..
You can imagine like this: First the (singularity) universe was a 1:infinity map with scale being 1/infinity, then after the big bang the map have been expanding to 1:10000000, 1:100000, and to 1:1000 .. (scale is enlarging).
The distance between galaxies in it does not change but the scale changes.

Now I enter again, humbled in the presence of you fellows and gals, with a possibly annoying quibble.

Is it possible that the nature of time itself is an issue here? What is time? I take it that it is somtimes a measuring stick, and sometimes that which the stick measures... not sure that these things fit a single continuum. If we cannot define this slippery commodity how can we even assign it so vast a quality as eternity, or limit it from such a quality?

Personally I think our temporal perceptions of the arrow of time are bound by the limitations of our nature, as consciousness first born and then dying: eternity is that which seemingly stretches "ahead" of us... but it is no less certainly that which precedes us. But is it possible that we have things exactly backward? If the flow of time were to reverse itself, would we even perceive the change?

In a way this goes back to an earlier query: why are we indeed in such a rush to put parenthesis on things? If as some thinkers posit physical space is a hall of mirrors, could not the same be true of time, in fact, WOULD not the same be true?

NPR's Talk of the Nation program had a very interesting program on this subject recently. You could access it at the NPR archives at NPR.org[/color]. Thanks to all here for the discussion.

Satts, I'm not doing so good.

If, as theorized by some proponents of the BB-EU Theory, the Observable Universe was smaller than say one wave length of greenish light cubed.
(500 millimicronsX500 millimicronsX500 millimicrons) then what happened?

Mechanically there must have been some change. Has the wave length of light shortend a bit?

Or are the Galaxies further apart, I realize that galaxies didn't exist then. (if there was a then)

Or none of the above? What could have resulted in todays observations? Speculations are welcome, labeled as such.

BBB

I think your modus operandi "says the most" here for what is philosophically(not scientifically) a pseudo-question. From a philosophical point of view, practically every word in the question (including "we") is "up for grabs". But from a scientific point of view Occam's principle leads to the preference for the simpler or "more elegant" of competing models. This point was omitted from ebrown's creditable original list.

Beedlesquionk,

Yes the nature of time does enter into it but it is not necessary to know what time is. It is only necessary to know how it interacts with what we percieve.

Same with light. We don't know what it is but we know pretty well how it interacts with time, matter,and gravity.

Matter of fact right now I am trying to determine a mechanical "speed of time". I think it exists but damned if I can figure out how to work it----YET.