# The universe?

Discussion in 'Physics & Math' started by god-of-course, Sep 20, 2003.

1. ### CanuteRegistered Senior Member

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1,923
James

If idealism is true then this view makes some sense. But I find it extremely difficult to make any sense of this from a physicalist perspective. It suggests that from the outside the universe is a point (metaphorically/ topologically) just as it has always been. The only thing I know of that has an internal extension greater than its external extension is the Tardis.

Is it not the case that either matter is eternal or something came from nothing?

Mmm. I'm not yet convinced.

3. ### leeausRegistered Senior Member

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265
In itself, your premiss is not enough to guarantee your conclusion here.

Hello JR Presuming you mean premise, care to back this statement up with a bit of logic or reasoning.

Regards leeaus

5. ### James RJust this guy, you know?Staff Member

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31,288
leeaus:

<i>Presuming you mean premise, care to back this statement up with a bit of logic or reasoning.</i>

I wrote "premiss". The spelling "premise" is an alternative. I'm not sure which one is preferable, but "premiss" is perfectly valid.

You said: "The fact that space consists of three dimensions at right angles to each other means space is limited."

A mathematical or physical dimension can have either finite or infinite extent. If a dimension is infinite in extent then a space containing that dimension is also infinite in size.

7. ### math/aceRegistered Member

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9
outside-> theory of everything, plus?

I suppose there could be something "outside" the universe - we just couldn't measure our distance to it b/c there would be no such distance.
In theory, there could be other "bubble" universes, each with their own space/time. Maybe there could even be a version of space and time between them, but it would be independent of the space/time IN each of them.
A thought - maybe it wouldn't be independent. Maybe each universe would "induce" a "local" space/time between universes that allowed universes to interact, much like gravity does between planets.
Man, I must be feeling very sci.fi.-ish today!
Still, that could explain dark-matter and dark-energy and such?
Maybe this needs its own post.

8. ### CanuteRegistered Senior Member

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1,923
James's universe was specified as being 'all that there is'. Therefore there cannot be anything outside it. It is a thing with an inside but no outside.

9. ### math/aceRegistered Member

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9
All there is?

The best definition that fits the most facts is that the universe is a four dimensional hypersphere that is *possibly* infinite. The past is toward the 4-D center of the sphere and the future is in the direction away from that (thus the illusion of an expanding universe - our awareness is constrained to only remember things that exist toward the center/past, but in reality the future is all there already in the farther regions of the 4-D sphere. The 3-D universe that we CAN see SEEMS TO BE expanding, but it is because our consciousness is seeming to "move" through the layers of this 4-D sphere like the layers of an onion. The entire perceivable universe AT ANY ONE TIME is a single layer, and each layer IS larger than the previous one.) Anyway, if the 4-D sphere is NOT infinite, there could be other universes beyond it. If it IS infinite, these relatively exciting times could one day be overpopulated by time-travellers avoiding the heat-death of the universe.

10. ### leeausRegistered Senior Member

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265
JR Not sure that you have supplied much logic or reason. The right angle means that any line in space is bisected by another line. Section A + section B = an infinite section runs counter to logic and reason.
Regards leeaus

11. ### James RJust this guy, you know?Staff Member

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leeaus:

<i>Not sure that you have supplied much logic or reason.</i>

Whatever.

<i>The right angle means that any line in space is bisected by another line.</i>

I don't see how that's relevant to anything.

<i>Section A + section B = an infinite section runs counter to logic and reason.</i>

Why?

12. ### leeausRegistered Senior Member

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265

A line of infinite length would encompass all distance.

Are you right so far or does that require further explanation.

Regards

leeaus

13. ### James RJust this guy, you know?Staff Member

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31,288
Ok so far. Do continue...

14. ### James RJust this guy, you know?Staff Member

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31,288
Ok so far. Do continue...

15. ### leeausRegistered Senior Member

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265
JR hello. Happy to continue if you want. Any line that encompasses all distance (a dimension in effect) is necessarily intersected by two other such lines.
That is just a statement that says there aren’t one but three dimensions.
Have you a problem with any of that? Shouldn't be to long and we will have your question answered.

Regards
Leeaus

16. ### James RJust this guy, you know?Staff Member

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31,288
leeaus:

<i>Happy to continue if you want. Any line that encompasses all distance (a dimension in effect) is necessarily intersected by two other such lines. That is just a statement that says there aren’t one but three dimensions.</i>

If that's all it is, I'm happy to accept it.

<i>Have you a problem with any of that? Shouldn't be to long and we will have your question answered.</i>

Not so far.

Let's try to keep our eyes on the ball here. Remember the eventual aim is to respond to this:

Do you think you'll get to an actual answer sometime soon?

17. ### thedIT GopherRegistered Senior Member

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1,105
To back James up here let us investigate the original claim.

Why do 3 perpendicular dimensions dictate a limit and not 2 or 4, say. Is there an a priori reason that 3 perpendicular dimensions dictate that space is limited.

We know that the sets of numerous scalar numbers can be unlimited or unbounded (infinite) in extent so there is nothing stopping any one 'dimension' being unbounded. It is after all just a construct representing a set of numbers so there is nothing stopping it being unbounded. The issue then becomes one of the dimensions being perpendicular. The corollary of this being that non-perpendicular dimensions (a Reimannian space for example) must be bounded or finite.

I strongly doubt that anyone can prove the above. It is a given that the Universe can be finite or infinite in extent yet still have a beginning.

My tuppeneths worth, anyway.

18. ### MacMRegistered Senior Member

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10,104
lethe,

ANS: You seem to be falling behind the times a bit.

MOND says Dark Energy is not required at all. We are not sure it is out there. Occam's Razor would favor MOND.

FOR WHAT IT IS WORTH.

But I can see where both MOND and vacuum energy could be involved.

Knowing to believe only half of
what you hear is a sign of
intelligence. Knowing which
half to believe will make you a
genius.

19. ### letheRegistered Senior Member

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2,009
i m behind the times? i find that unlikely. i follow all new developments of physics. i talk to people advancing the field, and read their papers. do you?

1. MOND solves dark matter, not dark energy. they are different. i didn t mention dark matter in my post at all, and frankly find dark matter kind of boring. MOND is completely unable to say anything about dark energy, since it is a cosmological phenomenon, and there is no MOND cosmology.

2. MOND faces serious experimental barriers, and may very well be incorrect. it certainly seemed promising for a time, if unsatisfactory. remember, MOND is not a fundamental theory, but just a phenomenological curve fitting power law.

3. also, dark matter has been measured by now from several independent methods. the first was the galactic rotation curve. MOND solves this problem. however, WMAP data (from a few months ago) and gravitational lensing all verify the amount of dark matter to surprising accuracy through independent tests. there is now little doubt in the scientific community about the presence of dark matter. it seems it is you who are behind the times.

20. ### leeausRegistered Senior Member

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265
JR Hello. We will get an answer sometime soon.
Your question actually was to do with an implication you made of the finite + the finite = the infinite. Allowing that you seem to believe that space is either finite or infinite at mathematical behest going a little further will not be a problem.

So we have established that any line in space is intersected by another line.

Moving along, neither portion of an intersected line can be of infinite length. That just comes from where we began when we reasoned out that an infinite line would encompass all distance. One section of the intersected line will not contain the other section. Therefore each section is finite.

Are you in dispute with that. The answer is probably getting to the obvious stage but are you settled with neither portion of an intersected line being of an infinite length due to neither section containing the length of the other section.

Regards
Leeaus.

21. ### MacMRegistered Senior Member

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10,104
lethe,

[Mac]: "MOND says Dark Energy is not required at all."

[Lethe]1. MOND solves dark matter, not dark energy. they are different.

Let me know if English is not your first language, I'll try to accomadate you.

My statement does not equate Dark Matter (MOND) to Dark Energy. It addresses a statement made regarding MOND mitigating the necessity for Dark Energy.

ANS: Not at all, I have read the reports and there is new evidence which falls outside of MOND but it is no clear yet if it can be reconciled or not.

Knowing to believe only half of
what you hear is a sign of
intelligence. Knowing which
half to believe will make you a
genius.

22. ### James RJust this guy, you know?Staff Member

Messages:
31,288
leeaus:

<i>Moving along, neither portion of an intersected line can be of infinite length. That just comes from where we began when we reasoned out that an infinite line would encompass all distance. One section of the intersected line will not contain the other section. Therefore each section is finite.</i>

Wrong. One infinity can contain another.

For example, the set of all integers has an infinite number of elements. The set of even numbers has exactly the same number of elements - still infinite.

If you cut a line of infinite length in half, each half still has infinite length.

23. ### letheRegistered Senior Member

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2,009
english is my native tongue.

now try to follow me here:

i mentioned dark energy. you said "lethe, check out MOND, it accounts for dark energy". i said: "MOND does not account for dark energy, it accounts for dark matter. they are not the same thing." my point was: MOND does not say that dark energy is not required. it says that dark matter is not required.

dark energy has nothing to do with MOND, MOND never said that dark energy was not required.

now what happened after that?