OT: Gravity, Dark Energy, Universal expansion - Page 4

Suicide Junkie · #31 January 6th, 2008, 05:20 PM

You're the one who said "twice as far away as the big bang"

Anyways...

I think the original point is that indeed there are places you can't get to from here.

Assume space is expanding at 20% per year, just for example, and the fastest you can go is 1 light year per year.
In such a case, attempting to travel to Sirius (8.6 ly away) is a bad idea.

Completely ignoring the compound interest you'll suffer:
In the first year, you'll get 1 lightyear along on your journey, leaving 7.6, but in the meantime that 7.6 will have stretched to 9.1
Light trying to get here from Sirius will suffer the same fate, and we wouldn't be able to see it.

MasterChiToes · #32 January 6th, 2008, 06:08 PM

I still wonder if that complete inability for two separate places in the universe to interact could cause some sort of spatial bifurcation (splitting of space)... very loosely analogous to the spontaneous splitting/radiating of a nucleus.

Suicide Junkie · #33 January 6th, 2008, 06:28 PM

If you had a set of points, A, B and C, where A and B were right at the limit of losing contact, and B and C were right at the limit of losing contact. B is located right in the middle between A and C.
A <-> B <-> C

Even though A and C can no longer see point B, you couldn't split the universe near B, because B would certainly notice

PS:
Of course, if there was some sort of a crack in spacetime, B would hardly be in a position to complain to management about it

MasterChiToes · #34 January 6th, 2008, 06:54 PM

Very true... but I was sort of referring to a radiative cross section... perhaps even a tipping point for spatial continuity. I guess a crack in spacetime might be one result.

Suicide Junkie · #35 January 6th, 2008, 07:05 PM

While you would have two regions that are independent, the space between them is still contiguous.

It is entirely possible to be unable to reach point C from point A, but at the same time be able to reach point B from point A and to reach point C from point B.

narf poit chez BOOM · #36 January 7th, 2008, 10:45 PM

...And here I thought another thread on physics was convinced there was no space-time, only particles and a void.

MasterChiToes · #37 January 7th, 2008, 10:48 PM

space-time happens after you drink the kool-aid.

Randallw · #38 January 7th, 2008, 11:10 PM

Might not the expansion be exponential (excuse me if I use the wrong word). The edge (14 Billion ly away maybe) might expand 20% but when something is only 8.6 ly away the distance moved might be inconsequential.

in fact since matter can not be created, unless there is a connection to another dimension, then the universe may expand but it has the same amount of matter, therefore imagine a distance written on a balloon. the edge expands but the distance expands at the same rate. to an outside observer it has grown but to something limited to the balloon it is the same distance.

Suicide Junkie · #39 January 8th, 2008, 01:16 AM

Except that the folks living on the balloon aren't expanding since they are held together by gravity, electromagnetism, and nuclear forces.

Light will take longer and longer to get from each of your distance marks to the next, making it obvious that they are stretching.

Randallw · #40 January 8th, 2008, 05:24 AM

I was sort of thinking of that epsiode of Futurama where the universe is in a box. Fry sits on the box and the universe is squashed, but since they are in the universe they don't notice. Only us outside observers. Probably a mistake to consider Futurama scientific fact

. After all they increased the speed of light.

"That's impossible"
"nothing's impossible. Not if you can imagine it. That's what being a scientist is all about"
"No, that's what being a magical elf is all about"