Universe Ending (my way of thinking it)

If you don't know where to post something, put it here and an administrator or moderator will move it to the right place.

Postby houserichichi » Tue Sep 19, 2006 11:15 pm

I stand happily corrected after a day of reading. Gravity seems to bind spacetime together on small scales and the expansion is only observable over great distances. This then leads me to question whether expansion is just so feebly small at local scales that we just can't detect it. At any rate, contracting the universe back to the singularity nugget that it came from and calling that "point" the center makes no sense unless you are assuming outright that the universe exists in some higher-dimensional embedding space. The big bang (and expansion that followed) is not an expansion in space but an expansion of space. Since accepted cosmology does not embed our universe in something higher there is no such thing as "center of expansion" nor "center of the universe". IF, however, we are embedded in something higher then yes, there really is a center but it is not in our universe.

If we reverse expansion then density grows, temperature grows, and physics as we know it breaks down...this is exactly why we have no answer as to "why" the big bang happened in the first place. As far as I can tell (now) it appears as though all matter would get closer together, not shrink along with the reversed-expansion.

As things get closer and closer the particles that make everything up become more disturbed. At the quantum scale the force of gravity is unbearably weak so I would imagine that the EM force would repel the charged particles. As space contracts there would be no room for repelled particles to escape to so they would shake violently around the ever decreasing space left. As they shook and jetted about the kinetic energy would result in an increase in thermal energy. As the (tiny) universe heated up particles would begin to dissociate themselves from eachother. In fact, we would reach energy scales that particles physicists would only dream of. We'd revert back to the quark-gluon soup and eventually our physics would break down entirely and we'd ultimately get our singularity, I suppose.

That's all just speculation as I'm by no means a professional cosmologist.
houserichichi
Tetronian
 
Posts: 590
Joined: Wed May 12, 2004 1:03 am
Location: Canada

Postby PWrong » Wed Sep 20, 2006 1:44 pm

oh yes and still on the topic of center. There is a center of mass, right? or is that circumvented by something else i don't know about?

That's an extremely interesting question, but for reasons that are pretty much irrelevent to this thread. I wonder if there is a way to define a centre of mass over non-euclidean space?

If you have a set of points distributed over the real line, the "centre of mass" is simply the average of the points i.e. add them up and divide by the number of points. But if we have a set of points spaced around a circle, is there any analogue of a centre of mass that remains on the circle?

If the points are evenly spaced, the centre is undefined (this is also the case with the universe). But if most of the points were up near the top, then we would have a centre of mass, also near the top. Does anyone know of a way to do this?
User avatar
PWrong
Pentonian
 
Posts: 1599
Joined: Fri Jan 30, 2004 8:21 am
Location: Perth, Australia

Postby moonlord » Wed Sep 20, 2006 5:02 pm

I thought of this:

Consider S1. Define "the coordinate" of a point to be the measure of the angle from a defined origin. Consider how it's done in trigonometry. The coordinate of the center of mass is a ponderate average on the coordinate of the considered points over their mass. Just like the way the center of mass is defined in E1, but instead of having lenghts you have measures of angles. Makes any sense?
Last edited by moonlord on Fri Sep 22, 2006 5:44 pm, edited 1 time in total.
"God does not play dice." -- Albert Einstein, early 1900's.
"Not only does God play dice, but... he sometimes throws them where we cannot see them." -- Stephen Hawking, late 1900's.
moonlord
Tetronian
 
Posts: 605
Joined: Fri Dec 02, 2005 7:01 pm
Location: CT, RO, CE EU

Postby thigle » Wed Sep 20, 2006 5:17 pm

i also always wondered what is centre of mass of a 4dimensional object ?

anyway, i dont know how to do it (in reply to pwrong's last question)
thigle
Tetronian
 
Posts: 388
Joined: Fri Jul 29, 2005 5:00 pm

Postby moonlord » Wed Sep 20, 2006 5:39 pm

The center of mass in Euclidean space is independent of the number of dimensions. Remember the Lorentz transfomations. That's why I consider only E1. Let x_i be the coordinates of the i=1..n points and m_i their mass.

The coordinate x_c of the center of mass is x_c = Sum[1<=i<=n](x_i * m_i) / Sum[1<=i<=n](m_i). Ponderate average.

[ Replace x_i with alpha_i, the angles between the origin and the points on a spherical space - S1 ]

Clearer now? I hope ... :)
"God does not play dice." -- Albert Einstein, early 1900's.
"Not only does God play dice, but... he sometimes throws them where we cannot see them." -- Stephen Hawking, late 1900's.
moonlord
Tetronian
 
Posts: 605
Joined: Fri Dec 02, 2005 7:01 pm
Location: CT, RO, CE EU

Postby PWrong » Thu Sep 21, 2006 3:31 am

What's a pondetare average?

You could just add up the angles and divide by the number of points, but I think that would depend on the coordinate system. If you did that with four points on the circle at {0, pi/2, pi, 3pi/2}, your centre of mass would be 3pi/4, and you could draw this point on the circle. But if you rotated the axes without moving the points, the angles would change, and your centre of mass would be different. :?
User avatar
PWrong
Pentonian
 
Posts: 1599
Joined: Fri Jan 30, 2004 8:21 am
Location: Perth, Australia

Postby moonlord » Fri Sep 22, 2006 5:47 pm

Oups a typo. A ponderate average is when you calculate for example the average mark of a class. If there are 10 with mark 10, 9 with mark 7 and 13 with mark 2, the average mark of the class is (10*10 + 9*7 + 13*2)/(10 + 9 + 13) -- that's a ponderate average. Don't know if the term is an english one, though :)
"God does not play dice." -- Albert Einstein, early 1900's.
"Not only does God play dice, but... he sometimes throws them where we cannot see them." -- Stephen Hawking, late 1900's.
moonlord
Tetronian
 
Posts: 605
Joined: Fri Dec 02, 2005 7:01 pm
Location: CT, RO, CE EU

Postby PWrong » Sat Sep 23, 2006 4:00 am

Ok, I've never heard that word before, but what you described is what I'd just call an average or a mean.

Anyway, I don't think that would work for points on a circle. We need a new type of average that's invariant to rotations. If we only have two points, they split the circle into two intervals. The average should choose the smaller interval, and put the centre of mass in the middle.

Here's an idea. Take the normal planar centre of mass (i.e. take the average x value, and the average y value). Now draw a line from the centre to the planar centre of mass. Continue this line until it hits the circle. This is the centre of mass we want. I'll try figuring out a formula for it.
User avatar
PWrong
Pentonian
 
Posts: 1599
Joined: Fri Jan 30, 2004 8:21 am
Location: Perth, Australia

Postby houserichichi » Sat Sep 23, 2006 4:26 am

Ponderate average = weighted average in English? That's what I see, anyway.
houserichichi
Tetronian
 
Posts: 590
Joined: Wed May 12, 2004 1:03 am
Location: Canada

Black Hole or Super Nova?

Postby Russ1953 » Wed Nov 15, 2006 7:51 pm

When a star starts to loose matter the fields are exaserbated (tish tish, my spelling) and expands to grab the missing mass to adjust the fields to temporial balance. If it is not sufficient it will reach beyond equal mass to control its radical dialation. If balanced is not achieved a nova effect is possible with the star taking the rest of its orbs in a jet stream of accelerated trajectory. If it its apeased proportionately it will settle. If by chance the balance of the fields is unaddressed and it reaches critical mass implosion to its heavy matter core will ignite a mass to dark matter transfer creating a black hole. Suffice it to say then that universe is in trouble. Consider a nueron when it splits the spacial distance between the split from its original location of the greater mass before the split where the 2 new matters end up could be another outcome of twin stars. The split will thrust each apart enough to either balance the fields between the 2 or split the immediate system regrouping the planets that orbit around them. That will be detremental to who gets what planet by field aquisition. In any sense continuity would be very abrupt to this planet.
Russ1953
Dionian
 
Posts: 40
Joined: Thu Nov 09, 2006 3:28 am

Postby PWrong » Thu Nov 16, 2006 3:44 am

Ok Russ. You'll be glad know that I've worked out the formula I was talking about.

Let x = Sum[ cos(theta<sub>i</sub>)] and let y = Sum[ sin(theta<sub>i</sub>)]

Then the average theta is arctan(y/x)
User avatar
PWrong
Pentonian
 
Posts: 1599
Joined: Fri Jan 30, 2004 8:21 am
Location: Perth, Australia

To PWRONG

Postby Russ1953 » Thu Nov 16, 2006 3:48 pm

Thanks for addressing an observative theorm. I'd be really cool if you'd break it down for me. I'd love to understand the math. I have found this site to be very cool and inspiring!
Russ1953
Dionian
 
Posts: 40
Joined: Thu Nov 09, 2006 3:28 am

Postby PWrong » Thu Nov 16, 2006 4:33 pm

Sorry for ignoring your first post. I had a look at it, but I think it warrants a new topic.

I'd be really cool if you'd break it down for me. I'd love to understand the math.

I'd be happy to explain it to you. How much maths do you know already? Are you familiar with sin and cos? The basic idea is that we have a bunch of points on the edge of a circle, and we're trying to find the "middle point", which is also on the circle.
User avatar
PWrong
Pentonian
 
Posts: 1599
Joined: Fri Jan 30, 2004 8:21 am
Location: Perth, Australia

Previous

Return to Where Should I Post This?

Who is online

Users browsing this forum: No registered users and 1 guest

cron