01-05-2003 00:00									#31
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quote: Well, what they tell you on these popular science programs on TV isn't true. Partilce, anti-particle pairs do not just spontaneously appear out of the a vacuum. There has to be something there for them to come. You kind of implicitly know this since you said 'from energy' - energy has to be in some form, eg. as a photon.

That's what I meant by energy.

Thanks for the explanation about the photon, and I am too young for the Higgs Boson.

	01-05-2003 00:02									#32
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quote: Originally posted by Azazel WAIT A SEC.......STOP!!!!!!! faster than light?

Yep!

There is no problem with the universe itself expanding at faster than the speed of light. The problem is only with exchanging information at the speed of light. Since everything is moving with the space-time expansion, you still can't send information faster than the speed of light so it is OK.

	01-05-2003 00:02									#33
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quote: Originally posted by Rogan Josh That's not true either. If the universe had expanded at the speed of light after the Big Bang then there would be no stars 14 billion light years away because we would see the Big Bang singularity itself 14 billion light years away (in all directions). Then, what you just said would be true - everyone, everywhere would have the same horizon, bounded by the Big bang singularity.

I have trouble conceptualising that scenario, unless you are saying that the universe would be a closed space of 14 billion l.y diameter. For you are effectively saying that everyone is at the 'centre' of a finite universe.

I'm not saying that this is not the case, I'm just saying we can't discount the alternatives as BG was.

	01-05-2003 00:05									#34
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"Brits seek missing WIMPS of universe"

Tell em to look across the channel.

	01-05-2003 00:09									#35
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quote: Originally posted by Big Crunch I have trouble conceptualising that scenario, unless you are saying that the universe would be a closed space of 14 billion l.y diameter. For you are effectively saying that everyone is at the 'centre' of a finite universe.

I get into difficulties with relativity here. What do we really mean by 'now'? As I am sure you know, the light which we see coming from stars in the sky is billions of years old, so we are seeing the star as it was billions of years ago. If you regard the 'universe' as being what lies along our past light cone, then yes it is a closed space of 14 billion years diameter- and you are sitting at the centre (since it is your light cone).

I would tend to think of the universe in a wider sense though.

	01-05-2003 00:14									#36
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quote: Originally posted by Rogan Josh I get into difficulties with relativity here. What do we really mean by 'now'? As I am sure you know, the light which we see coming from stars in the sky is billions of years old, so we are seeing the star as it was billions of years ago. If you regard the 'universe' as being what lies along our past light cone, then yes it is a closed space of 14 billion years diameter- and you are sitting at the centre (since it is your light cone). I would tend to think of the universe in a wider sense though.

In this instance I am refering to the totality. If you could freeze the universe in space and time what would a map of it look like when all parts are the same age (or rather same stage of development).

	01-05-2003 00:15									#37
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quote: Yep! There is no problem with the universe itself expanding at faster than the speed of light. The problem is only with exchanging information at the speed of light. Since everything is moving with the space-time expansion, you still can't send information faster than the speed of light so it is OK.

Oh, I got it, the space itself was expanding, and so was the matter in that space, and on agreggate the speed was faster than light.

My question is, if space/time itself was expanding, what point of reference can one have?

	01-05-2003 00:18									#38
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RJ, let me clarrify my thinking for you, so you can correct me if I'm missing stuff.

If you consider an explosion from a point in flat or open space there will always be parts that are at the edge of the matter conglomerate, and bits left in the middle. They will all have different perspectives

In a closed space explosion you can have all particles touching another particle from the explosion. They all have the same view.



I don't *know* if that is true, but that is my visual aide, and fits in with what I remember from maths classes.

	01-05-2003 00:23									#39
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Yes BC, that seems right to me.

Sorry Azazel - I don't understand your question.

	01-05-2003 00:28									#40
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well, if Space/time itself expands, what does it expand over?

If space time expands, a meter in a certain direction becomes longer as time passes by. correct? But if a meter becomes longer with time, what stays the same?

	01-05-2003 00:52									#41
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quote: Originally posted by Azazel well, if Space/time itself expands, what does it expand over? If space time expands, a meter in a certain direction becomes longer as time passes by. correct? But if a meter becomes longer with time, what stays the same?

That is a very good question. I actually asked this very question myself to about 10 different cosmologists before I could find one who even understood my question.

The answer (as I understand it - I am not a cosmologist) is that the expansion is only occuring at large scales. So you are not getting any bigger. It is only the measure of distances at large scales (like Earth to the Orion nebula) which are expanding. To make a bad analogy, imagine an explosion which send lumps of rock flying in all directions - the distance between the rocks grows but the rocks themselves don't.

	01-05-2003 01:06									#42
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So let me get this straight, while, say a human being grows say, 2% in length, a planet grows 10%? No, this can't be right. you probably mean that the change is only noticeable on extremely large scales. Also, as I understand OBJECTS don't grow, it's the space that does?

generally, something smells fishy in this. I understand that we're pretty much at the frontiers of human understanding of the universe, right?


I feel missing out, that I didn't go studying in that direction in Uni. Cosmology always fascinated me as a kid. ( But who wasn't fascinated by cosmology as a kid, right? )

	01-05-2003 01:13									#43
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Does the universe have an edge? If so, then what happens when light reaches the edge of the universe? It can't cross the boundary since there is nothing on the other side, and it can't simply dissapear because that would be a violation of the law of conservation of energy. It seems to me that the only possibility is that the light would reflect off of the boundary and come back towards us. But if this is the case, then it would mean we are essentially surrounded by a cosmic mirror in all directions. In such a case, everything would be reflected ad infinitum, and it would mean that most of the galaxies we see are actually just multiple reflections of closer ones.

	01-05-2003 01:14									#44
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The universe doesn't have an edge, as apparently ( ), if you go one way real far, you'll come out of the other end.

	01-05-2003 01:16									#45
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quote: Scientists around the world are racing to be the first to discover the truth about Dark Matter, which cannot be seen because it does not emit light. They believe it makes up the vast majority of the universe.

I don't get this. Not everything that can be seen emits light, a lot/most of it reflects light, right? What the heck are they saying dark matter is? Mini Black holes?

quote: well, if Space/time itself expands, what does it expand over?

I like to think that it is not expanding over something, but into something. That something is something like a Bizarro universe where everything is opposite of what it is here. This could explain a lot, and I am to lazy to explain it. Has something to do with matter/anti-matter relations and entropy. Kind of like a magnetic spring/coil expanding from the big bang, it will eventually reach its full potential energy, at which time all real entropy will be disipated, but concurently bizzaro entropy will be at it's max... and BANG!

Then again, it could just be expanding over a banana

	01-05-2003 01:21									#46
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Bizzarro Universe! It all makes sense now! ROTFLMAO.

Sorry. I just couldn't hold myself.

	01-05-2003 01:32									#47
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quote: Originally posted by Azazel So let me get this straight, while, say a human being grows say, 2% in length, a planet grows 10%? No, this can't be right. you probably mean that the change is only noticeable on extremely large scales. Also, as I understand OBJECTS don't grow, it's the space that does?

Yes, I mean that the change is only noticeable on really large scales. In fact, even our galaxy isn't expanding with space-time. It is larger scale than that. It is due to what is the dominant force for the object.

Let me give another analogy. When you get into a roller coster, different parts of your body are accelarated at different rate, but your body doesn't fly apart because the molecular bond holding you together are stronger than the forces that the roller coster exerts.

Similarly, the bonds in your body are far stronger than the expansion of the universe, so you stay the same size. Even gravity is stronger, so the moon-Earth distance isn't increasing. Even distances within out our galaxy aren't increasing because gravity holds it together. It is only really far distances, where gravity is extremely weak (remember it goes down like 1/distance^2) that the expansion of the universe is dominant.

	01-05-2003 01:33									#48
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quote: Originally posted by Azazel The universe doesn't have an edge, as apparently ( ), if you go one way real far, you'll come out of the other end.

Or if it isn't spherical, you will keep going forever....

	01-05-2003 01:36									#49
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I don't think that "Spherical" is the best way to describe it. Unless it's a 5 (?)- Dimentional sphere.

(My poor brain. Just had a Diff. Eq. test, and now this? )

	01-05-2003 01:37									#50
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Sheessh, just think "Sliders", it's all there!

	01-05-2003 01:38									#51
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quote: Originally posted by Japher I don't get this. Not everything that can be seen emits light, a lot/most of it reflects light, right? What the heck are they saying dark matter is? Mini Black holes?

Everything you 'see' (ie. with your eyes) is emitting light. Light hits it, is absorbed, and remitted. You can build up a picture of what is there because it is interacting with light.

Things which to not interact with light, you will not see. A gas, for example lets (most of) the light pass straight through, so you don't see it.

Similarly, the particles they are looking for do not interact with light. Actually, anything which doesn't have an electric charge will not interact with light. They are being a little simplistic in the article - the point about WIMPS is they almost don't interact with anything at all!

	01-05-2003 01:42									#52
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Yep, That's the theory. It doesn't make sense, though.

	01-05-2003 01:48									#53
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Why not?

	01-05-2003 01:52									#54
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quote: Originally posted by Rogan Josh (This is all supposition of course - the universe could be spherical (and therefore not infinite) for all we know.: travel in one direction long enough and come back to where you started.)

Or Donut shaped.

Mmmm... Donuts...

	01-05-2003 01:54									#55
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quote: Originally posted by Azazel well, if Space/time itself expands, what does it expand over?

Think about a balloon as it expands...

Now, imagine that that balloon represents a 2-D universe to the inhabittants in the rubber of that balloon as the balloon expands in a third direction.

Now add a dimension to take the analogy to our universe.. Poof, viola.

(Of course, IIRC, there's something like at least 7+ dimensions in our universe... )

	01-05-2003 01:55									#56
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quote: Why not?

I'm a MACHO man . Yes, I know there are not nearly enough of them, until I'll see solid proof of those particles, I'll stick with the familiar. I don't know why, really.

	01-05-2003 01:59									#57
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Rogan: thanks for the tutorial.

I never thought of the light being remitted more so reflected. After some quick research I found that I was both right and wrong.

good lesson

Sad, isn't it, that I have a degree in chemical engineering and my physics is so bad. It has been some time since I have had to do anything with optics.

I still don't get thier theory on this Dark Matter. If it doesn't interact with anything at all, then how can it exist? Is this some sort of neutron? A mass without a charge? Odd, sounds to be stupid theory to me, but hey.

	01-05-2003 01:59									#58
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Edan: why do you say there are 7+ dimensions? Last time I looked, there were 4.

	01-05-2003 02:02									#59
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quote: Originally posted by Rogan Josh Edan: why do you say there are 7+ dimensions? Last time I looked, there were 4.

Are you considering time as one of those dimensions? Simply because you can't see a dimension, doesn't mean it isnt there.

String Theory requires something like 7 or 11 dimensions, etc And then theres all that other fun higher order physics stuff...

However, even ignoring time, there would have to be four extra dimensions. Consider the balloon example. That has 3 dimensions for a 2D balloon person, without time being added in - and yet those 2D balloon people can't see the third dimension. To them. the world only goes in two directions, in the balloon...

	01-05-2003 02:03									#60
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quote: Originally posted by Japher I still don't get thier theory on this Dark Matter. If it doesn't interact with anything at all, then how can it exist? Is this some sort of neutron? A mass without a charge? Odd, sounds to be stupid theory to me, but hey.

It does interact. It just interacts really really weakly. If it didn't interact at all the experiment in the Boulby mine would be pretty pointless, because they obviously wouldn't detect anything!

Yes, they have no charge, like a neutron. Why do you think this sound stupid?