The Big Bang Theory

[Choobus]

a different tim wrote

......you don't need extra dimensions to explain the big bang.

You don't want them really. If you write Einsteins field equations in N+3 spatial dimensions and let the universe expand from a point where the N dimensions are of the same size as the three the solution naturally leans towards a split in the nature of the two groups of spatial dimenstions, with the N (which can be any finite number) getting progressively smaller. This isn't a compactification model because it just assigns different properties two the dimensions indicating that the solution to the ordinary GR field equations is more stable with 3 spatial dimensions. Having more dimensions is a pain in the arse. (One can of course alter the equations to avoid this, but this is very contrived).

[Kate]

[psychodiva]

Choobus wrote

You don't want them really. If you write Einsteins field equations in N+3 spatial dimensions and let the universe expand from a point where the N dimensions are of the same size as the three the solution naturally leans towards a split in the nature of the two groups of spatial dimenstions, with the N (which can be any finite number) getting progressively smaller. This isn't a compactification model because it just assigns different properties two the dimensions indicating that the solution to the ordinary GR field equations is more stable with 3 spatial dimensions. Having more dimensions is a pain in the arse. (One can of course alter the equations to avoid this, but this is very contrived).

well- I understand each individual word of that but put the whole together and I'm lost- so- I will just keep lurking and trying to learn

Purely hobby, reading in spare time. I'm an IT so I sit around (waiting for people to "break" their computers) reading blogs and such all day, following links to new stories etc, and if there's something I've never heard about I go try to find whatever I can on the subject. I'm currently going back to school to get a degree in Biology and I'd like to do some Master's work and possible Doctoral. Did I say something blatantly wrong, if so I'd like to know so I can correct it. That tennis ball thing was from Astronomer Alex Filippenko.

psychodiva wrote

well- I understand each individual word of that but put the whole together and I'm lost- so- I will just keep lurking and trying to learn

I'm with you on this one... when Choobus isn't telling someone to fuck off, or linking pictures of shit streaks in tighty whiteys, he really knows his shit and it makes me feel pretty damn ignorant.

[Choobus]

Are you implying that when telling someone to fuck off I don't know what I'm talking about?

There's no reason you should feel ignorant for not knowing what I had to go to school for 10 years to learn.

[Kate]

zer0 wrote

I'm an IT so I sit around (waiting for people to "break" their computers)

I got to submit a trouble ticket yesterday, and I wrote "unable to map to workstation".

Fastest response I ever got.

Choobus wrote

Having more dimensions is a pain in the arse. (One can of course alter the equations to avoid this, but this is very contrived).

i take it you're not a fan of string theory then?

[Kate]

[Choobus]

String theory is ok, but I like physics much more than matehmatics.

Well I meant ignorant as in "lack of knowledge of a specific subject" so I really don't have a problem admitting ignorance. I think the world would be a lot better off if people would just admit their ignorance more often.

[nkb]

zer0 wrote

Purely hobby, reading in spare time. I'm an IT so I sit around (waiting for people to "break" their computers) reading blogs and such all day, following links to new stories etc, and if there's something I've never heard about I go try to find whatever I can on the subject. I'm currently going back to school to get a degree in Biology and I'd like to do some Master's work and possible Doctoral. Did I say something blatantly wrong, if so I'd like to know so I can correct it. That tennis ball thing was from Astronomer Alex Filippenko.

No, not at all. I don't have anywhere near the requisite physics expertise to call you out on anything that complicated.

You speak on the subject authoritatively (and have not been slapped down by the experts here), so I was just curious about your background.

I just wish I had more time to get deeper into this kind of stuff, but having young kids at home has a way of cutting your free time down to nothing. I envy people like you.

[Sternwallow]

VladTheImpaler wrote

Thanks ADT!



I still have a problem with this.

If we reach the conclusion that the universe is 13.7 billion years old because we are able to detect light in every direction from Earth 13.7 billion light years away then does that not suggest that we are in the centre of the expansion?

For you to understand my thinking lets hypothesize that we moved 6 billion light years in one direction away from the Earth. Then from this position should you not be able to gaze 13.7 billion light years into the direction towards Earth and beyond while only 7.7 billion light years into the opposite direction?

If not how do we know the universe is 13.7 billion years old? I don’t get it…

I’m just trying to visualize the universe as a whole in relation to our selves and under the Big Bang Theory my mind tries to visualise a spherical universe.

I see, very interesting!

I guess the question is then why is space expanding?

A train left Chicago bound for LA. As it passes a station in Nevada, it is noted that the train is going 60 MPH. How long ago did it leave Chicago? Answer: the distance in miles between the station and Chicago expressed as minutes. So, if the galaxies are moving apart at a known rate and they are a known distance apart, simple division yields the point in time when they were all in the same spot. It gets trickier if the expansion rate is not constant and even more so if the rate of change is, itself, changing, but the calculating principle is the same. Miles/Miles-per-hour = Hours.


Things expand when they are affected by a force or when they obey momentum caused by a force in the past. Thus, if we observe expansion in the form of galaxies moving away from each other, it is reasonable to postulate a force even though other characteristics of such a force are not known. Thus we have "Dark Energy". Similarly, if a galaxy rotates too fast for the gravity of the detectable mass to hold it together, then there must be enough more undetected mass to make up the deficit. Thus we have "Dark Matter". We don't know what dark Mater is either, but now, using the galactic rotation effect, we can detect it and measure it.

[Choobus]

galaxies are moving in space, and space is itself expanding, so it's a bit more complicated than that. Galaxies could move apart from each other with no forces acting on them just by virtue of the expansion of the universe.

[Sternwallow]

VladTheImpaler wrote

I understand the concept but I can't for the life of me visualize or grasp what this actually means in practical terms in relation to a three dimensional universe.

If there is no centre then how can the Big Bang have originated from a single super massive and dense point?

Did the explosion or expansion from the Big Bang expand “into the emptiness” to create the universe or was the super massive and dense point that lead to the Big Bang the entire universe in itself and space/time expanded “within it”? Heh? Does this make any sense?

The common description that I visualize is that, when all of the universe was compressed into a single point, that point was the center of the universe (where else can it be when there is no where else?). So, as the universe expanded, that is, as space expanded, the universe remained the center. IOW it is equally true that there is no center and that everywhere is the center.

In principle, if light traveled in a "true" straight line (that is, unaffected by gravity) and if it went at infinite speed, you could use a telescope to look at the back of your own head, the light from it traversing the closed (finite but unbounded) universe around and back to your eye.