# Wolv1's questions about causality and particles

Discussion in 'Physics & Math' started by Wolv1, Aug 25, 2008.

1. ### ReikuBannedBanned

Messages:
11,238
For a better set of words, some scientists believe you can enter a black hole that is large enough, and entered very carefully. Hawking now believes you can't enter a black hole, because your particles would be mangled, and then quantum tunneled out of the black hole, and back into spacetime. Some scientists don't even believe black holes exist. So you see, it is very difficult to have an absolute model, that we can say (is the correct one).

3. ### Wolv1BannedBanned

Messages:
322
i know that godel's metric cant work becuase the universe does not rotate,what does kerr's metric need to obtain a ctc?

Messages:
11,238
Not sure.

7. ### Wolv1BannedBanned

Messages:
322
tipler's time machine have ctc's,but only if it's infinintly long?, also a ctc would be in the singulartiy?

8. ### ReikuBannedBanned

Messages:
11,238
I had never heard of the ''infinite long'' part of the machine. I also was curious of this.

A singularity, can be thought of a curve in spacetime: An infinite curvature to be correct.

9. ### Wolv1BannedBanned

Messages:
322
ya it says tippler's time machine would only go back in time if it were infinintly long,on the wiki page.

10. ### ReikuBannedBanned

Messages:
11,238
Ok. It's just i had never heard of this. I never doubted Oli though.

11. ### ReikuBannedBanned

Messages:
11,238
I'm not sure how Tipler would ever get a time machine to extend into infinity. It's a bit of a cop-out in that respect, nothing but waisted mathematics.

12. ### ReikuBannedBanned

Messages:
11,238
Very dissappointed

Messages:
322

14. ### Wolv1BannedBanned

Messages:
322
but black hole's have evidence and ctc's dont?

15. ### ReikuBannedBanned

Messages:
11,238
Black Holes evidence, is indirect. Anything goes, at the moment.

16. ### Wolv1BannedBanned

Messages:
322
so i read it right? that it has to be infinite? sorry a little tired.

17. ### Wolv1BannedBanned

Messages:
322
that it has to be infinite?

18. ### ReikuBannedBanned

Messages:
11,238
You're tired!

I've been up practically all night worrying about a test today at collage :bawl:

Yes, i am a bit dissappointed the machine he proposed, isn't exactly constructable. Not within our capabilities anyway, to make an infinitely extending time machine.

19. ### Wolv1BannedBanned

Messages:
322
ya,it sucks it has to be infinite.you don't mind me asking what are you studying?

20. ### ReikuBannedBanned

Messages:
11,238
Physics, Chemistry, Biology and (now) Math.

21. ### Guest254Valued Senior Member

Messages:
1,056
Any compact spacetime admits closed, timelike curves.

Sketch proof: let $I^+ (p)$ denote interior of the future lightcone of the point $p\in M$. Use $\tau = \{I^+(p)\, :\, p\in M\}$ as an open cover of $M$, and since $M$ is compact we may assume wlog that this cover is finite so $\tau = \{ I^+(p_1), I^+ (p_2) , \ldots, I^+ (p_n)\}$. Also wlog assume that no $I^+(p_i)$ is contained in some $I^+ (p_j)$ (since we could just make a finer cover removing the unwanted open set). But because of this, it follows that $p_1$ is not in $I^+(p_i)$ for $2\leq i \leq n$, and so $p_1$ is in $I^+(p_1)$, hence there exists a closed timelike curve in $M$.

Awesome.

22. ### Wolv1BannedBanned

Messages:
322
but closed timelike curves arent real know to exist?

Messages:
322