# Why can't I do this?

1. Mar 30, 2006

### tribdog

say I make a wormhole, a big one. that instead of connecting two places in space it connects two places in time. something that goes in one end comes out the other 1 second earlier. Then I throw in a black hole. which goes back in time and comes out the other end and now i have two black holes which go in and now I have four then eight etc. can I now reverse the big bang with all my extra gravity?

2. Mar 30, 2006

### DaveC426913

Last edited by a moderator: May 2, 2017
3. Mar 30, 2006

### tribdog

so I can't do it because Mr. Sawyer says so?

4. Mar 30, 2006

### pervect

Staff Emeritus
I'm not sure how well a wormhole will accomodate a black hole.

As far as the energy conservation issues go, the entracne wormhole mouth will gain all the mass of anything that passes through it, and the exit wormhole mouth will lose that mass. So the total mass at both ends of the wormhole remains constant.

Thus if black holes could pass through wormholes without any problems (I don't know the answer to this, as I mentioned), on the exit side you'd have a large negative mass wormhole mouth together with a bunch of smaller positive mass black holes, but the total mass on the exit side of the wormhole before and after the emergence of the black holes wouldn't change.

Note: this implicitly assumes that you have an isolated section of the universe to play with, one that has an asymptotically flat space-time, so that you can measure the mass.

See for instance
http://www.npl.washington.edu/av/altvw69.html

Note that this creates some stability issues, as Cramer goes on to discuss. Also note that while this article appeared in a science fiction magazine, it is a factual (popular-level) article by a professional physicist who also writes science fiction.

Last edited: Mar 30, 2006
5. Mar 31, 2006

### AlphaNumeric

Would the worm holes mouth not then violate the positive energy theorem?

6. Apr 23, 2006

### Romanus

I think physicists have postulated something like this for a long time. The basic mechanism would involve putting one "end" of a wormhole in a deep gravity well, such as very near a neutron star or black hole, where gravitational time dilation would pile up an offset between the two ends. When you get the right delay, then move the business end away from the neutron star/black hole, and you have an instant time--and space--machine