Maybe we got this all wrong...

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Maybe we got this all wrong...

Postby blue_bird_96 » Mon Feb 23, 2004 12:19 am

As far as we all can see, the universe is infinite. BUT!! What if we're wrong in that theory? Then everything we think we know about tetraspace wrong, just because we think the universe is infinite. Then our theory of time and space is wrong... I'm so confused, my brain is overloaded, WAAAY too much for a 13-year olds mind :? :shock: :?
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Postby RQ » Mon Feb 23, 2004 4:41 am

The universe isn't infinite, for one very simplistic reason explained in Hawking's a theory of everything.
If it were infinite, then the night sky would be as bright as the day, since all the infinite stars would send light, and even if there was matter as suggested in the 1800s by a scientist (forgot his name), it would be so heated up until it glows. If there are infinite objects, then they would be overwhelmed by the number of stars, and Cantor sets would explain why there would be "more" infinite stars than objects. Besides, relativity explains that this universe must be curled up in the 4th dimension, so in whatever direction we traveled for whatever amount of time, we would eventually come back to the same point of space we left.
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Postby Aale de Winkel » Mon Feb 23, 2004 8:21 am

RQ wrote: Besides, relativity explains that this universe must be curled up in the 4th dimension.


I don't know wheter you are aware of the possibility to edit once postings, it may make thing more readable when you do!

I don't know whether the universe is curled up in the fourth dimension, it might well be the picture our puny trionian brains need to deal with Riemanian curvature.
The curves in space is generated by gravity, and is the reason why we can see stars that would otherwise be hidden by the sun. I see this as a feature of the universe itself, which is curved on its own by the internal object excerting gravity on its surroundings.
In principle there thus is no need to see a fourth dimension behind this feature, and that 4th dimension might thus well be a figment of our imagination. :twisted:
Due to this curvature the earth is moving in a straight line around the sun :lol:
.
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Postby Geosphere » Mon Feb 23, 2004 7:13 pm

Where are you coming up with the universe is infinite?
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Postby PWrong » Wed Feb 25, 2004 1:44 am

The idea that the universe is infinite is actually pretty old now. Since the big bang, the universe has been expanding, and the expansion is apparrently accelerating, but the size of the universe is still finite.

RQ, you're mixing up relativity, string theory, and another completely different theory. Relativity says that spacetime is curved into the 4th dimension, while string theory says that it's curled up in 9 or ten dimensions, but only at small scales. The theory you're trying to describe says that the universe is like the surface of a sphere, or the surcell of a glome, so you can come back to the same point if you travel long enough. That's not widely accepted yet, it's just one of many theories.
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Postby blue_bird_96 » Wed Feb 25, 2004 7:58 pm

This makes understanding the fourth dimension a whole lot easier now, thanx!! I should read other theories before learning about more complicated ones. :)
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Postby RQ » Thu Feb 26, 2004 2:37 pm

A lot of it was pretty much summarizing Hawking. Although not everybody has agreed upon whether the universe is curled up in a glome, that is from what I was told what relativity predicts. And for what I know about string theory is, that if you represent the dimensions as units where there are only lattice points then there are 7 dimensions to go, and lengths with nonlattice points are the regular 3.(Dont quote me here).
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Postby PWrong » Mon Mar 01, 2004 10:30 am

Einstein invented relativity very soon after the possibility of extra dimensions had been proposed. Relativity and string theory are the only actual "theories" that use extra dimensions.

The rest, like the universe being like the surcell of a glome, is more of a popular speculation. It's a lot easier for the public to understand, and it helps science fiction authors to move characters around, but the shape of the whole universe isn't really that important to physicists.

By the way, RQ, I didn't say, "curled up in a glome". That's completely different from the surcell of a glome. If you paraphrase someone, do it properly, or just quote directly.

The best way to learn about string theory is to read The Elegant Universe. I don't think anyone could explain it better than Brian Greene does. Sorry if this makes me a heretic, but I think he's a better author than Hawking.[/quote]
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Postby RQ » Tue Mar 02, 2004 6:43 am

Well I meant just as a plane curled up in a sphere, our universe is curved the same way.
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Postby elpenmaster » Fri Mar 05, 2004 6:58 am

my conception of the matter was that the 3-d universe is the surcell of a glome, and that gravity bends the surcell into the inside of the glome. since gravity obviously exists, wouldnt this nessecitate the fact that the 3-d universe is the surface of a glome?
please pardon my cartesian logic
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Postby PWrong » Mon Mar 08, 2004 9:20 am

A plane isn't curled up inside a sphere, it's the surface of the sphere.

The 3D universe doesn't have to be the surcell of a glome. It could be the surcell of a tetracube, or another shape, or just a tarrow swock, curved upsilon. (I'm using the terms without explanation to encourage new members to read the introduction before they post anything).

In fact, we don't know for certain that spacetime is curved at all. It certainly seems that way according to relativity, but it's mostly just a way to describe the universe. and predicted. Other explanations exist that predict the same the relativistic effects.

I read an idea in The Elegant Universe about gravitons being the threads in the fabric of spacetime, that can stretch, become tense, and exert a force on matter. This theory doesn't involve curving into the fourth large dimension, although it's part of string theory, so it does have extra smaller dimensions.
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Postby PepsiCola » Wed Mar 17, 2004 4:06 am

RQ wrote:The universe isn't infinite, for one very simplistic reason explained in Hawking's a theory of everything.
If it were infinite, then the night sky would be as bright as the day, since all the infinite stars would send light, and even if there was matter as suggested in the 1800s by a scientist (forgot his name), it would be so heated up until it glows.


That's one of the dumbest assumptions I've heard.
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Postby PWrong » Wed Mar 17, 2004 11:25 am

PepsiCola wrote:
RQ wrote:The universe isn't infinite, for one very simplistic reason explained in Hawking's a theory of everything.
If it were infinite, then the night sky would be as bright as the day, since all the infinite stars would send light, and even if there was matter as suggested in the 1800s by a scientist (forgot his name), it would be so heated up until it glows.


That's one of the dumbest assumptions I've heard.


As much as I'd like to agree with you, the assumption itself isn't actually dumb. Hawking explains it in more detail, but it doesn't really matter today. We know the universe is infinite because we know exactly how big it is, how much matter is in it, and how much dark matter is in it.

Speaking of dark matter, could that be something to do with the 4th dimension? Probably not a good thing to ask here. I'll post a new thread on it tomorrow.
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Postby elpenmaster » Sat Mar 20, 2004 5:04 am

how do we know that the universe is infinite?
if the universe is infinite, how would we know how much matter is in it?
wouldnt there then be infinite matter?
:)
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Postby RQ » Sat Mar 20, 2004 5:08 am

You know, calling it an assumption, and then dumb, you must be pretty ignorant and arrogant. I mean, if you actually read a book, it might clear up some "smart" questions, I probably wouldn't ask since I'm stupid.
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Postby elpenmaster » Sat Mar 20, 2004 5:55 am

thank you for you r brilliant personal mental analysis of me
but unfortunatetley i am stupid as well
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Postby PWrong » Sat Mar 20, 2004 6:31 am

Ooh, sorry. :oops:
I meant to say we know the universe isn't infinite.
Wow, this is embarrassing. I usually try really hard to get everything right, and now I've confused everyone.

It's nothing to do with being stupid. If any of us were stupid we wouldn't be talking about cosmology. It is important to read books on the matter, but it's almost impossible to paraphrase part of a science book and get it right. But can we try not to insult each other?
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Postby elpenmaster » Sun Mar 21, 2004 6:30 am

sorry i thought you were talking to me, pwrong
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Postby RQ » Sun Mar 21, 2004 8:52 pm

Yeah well tell that to pepsi cola over there.
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Postby Nick » Sat May 06, 2006 1:12 pm

PepsiCola wrote:
RQ wrote:The universe isn't infinite, for one very simplistic reason explained in Hawking's a theory of everything.
If it were infinite, then the night sky would be as bright as the day, since all the infinite stars would send light, and even if there was matter as suggested in the 1800s by a scientist (forgot his name), it would be so heated up until it glows.


That's one of the dumbest assumptions I've heard.


I agree with PepsiCola, though I wouldn't call Stephen Hawking dumb. If the Universe was infinite, then the night wouldn't necessarily be filled up with stars... the light from the stars might not have reached Earth yet.
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Postby Keiji » Sat May 06, 2006 5:54 pm

... What's with the major bump? (this topic is over two years old...)
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Postby Nick » Sun May 07, 2006 3:37 am

iNVERTED wrote:... What's with the major bump? (this topic is over two years old...)


I'm just browsing through the old topics. Seriously, if we stopped posting on old topics, what's the point of keeping them on the website? :P
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Postby bo198214 » Sun May 07, 2006 8:14 am

Can anyone tell me what you (all) mean by infinite?
From the discussions (argument of Hawking) I would guess you mean infinite mass.
Or do you really mean volume (for example if the universe could be imagined as a closed surface in 4 dimensional space)?
In the latter case it would helpful to describe how one then measures the 3d volume from inside the 3d space.
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Postby Nick » Sun May 07, 2006 11:46 am

bo198214 wrote:Or do you really mean volume (for example if the universe could be imagined as a closed surface in 4 dimensional space)?
In the latter case it would helpful to describe how one then measures the 3d volume from inside the 3d space.


That's what we mean :).
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Re: Maybe we got this all wrong...

Postby Rkyeun » Wed Jun 03, 2009 6:28 pm

If the universe were infinite in time and space, then in any direction we cared to look into space there would be a star, reflective object, or black body, and its light would reach us by virtue of having singled it out if it had happened to emit a photon in our direction at that instant. This decreases the further away an object gets, as it only has finitely many photons to send and they get further apart as they travel until the object is dark by virtue of all its photons having missed us. From there comes the inverse square law. But at that same field of view as distance increases there are direct square more space to view, which we assume contains stars with the same frequency (namely that frequency is "Yes"). And so the chances of us seeing that lucky photon are also "Yes" and the night sky must be staring directly into the surface of the sun. It is not, so either the universe is not infinite in time and thus light from distant regions hasn't reached us yet, or the universe is not infinite in space and those stars do not exist to observe, or some combination of both.
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