# What's the matter: time travel paradox **URL:** \ **Category:** Great Debates\ **Created:** [December 9, 2003, 3:47pm UTC](https://boards.straightdope.com/t/whats-the-matter-time-travel-paradox/217938 "2003-12-09T15:47:06Z")\ **Posts on this page:** 2\ **Page:** 2
**Author:** ![Chicago\_Faucet](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/chicago_faucet/32/13910_2.png) [@Chicago\_Faucet](https://boards.straightdope.com/u/Chicago_Faucet)\ **Post date:** [December 15, 2003, 7:18pm UTC](https://boards.straightdope.com/t/whats-the-matter-time-travel-paradox/217938/21 "2003-12-15T19:18:36Z")
> [@](#): > > \*Originally posted by Scylla \* > \*\*Just thought of something else. > > It isn’t a problem at all. > > In one of those tricky dick paradox thingies it comes clear. > > When the future sends Schwarzenegger back in time it creates a deficit in mass/energy, right? > > There’s too much mass/energy in the past and not enough in the future, right? There’s a defecit in the future and a surplus in the past. > > Eventually though time goes on in the past. The years go by and finally we are at the point where Arnie was sent back. At that point in time when they send Arnie back they correct the surplus and balance everything out. > > So actually it would violate the conservation of mass/energy if they **didn’t** send Schwarzenegger back. Why? Because they did. > > The only way that you could screw things up would be by sending Schwarzenegger back so that he changes the past so that they end up not Schwarzenegger back in the future. > > Of course, by definition this is impossible. If they sent Arnie back then they did. If they didn’t, they didn’t. > > So, to answer your original question, not only does it not violate the laws of physics to send Schwarzeneger back in time, it is specifically required that it happen by the laws of physics. > > This is one of those things that’s obvious if you’re a Conservative. That’s why liberals shouldn’t be allowed to mess with the space/time continuum. \*\* Actually, I do see a problem with this. The problem is that the mass of material that made up The Terminator in the future already exists in the past. It exists in the present up until it gets put into The Terminator, and sent back in time, never to return. But one thing about The Terminator movies. They initially sent one back in time to kill Sarah Connor. As soon as they sent it back in time, if Connor Jr. didn’t immediately cease to exist, then they would know that The Terminator failed. What would they then do? Send back another Terminator, and another, until the job was done. Just because you defeated one, doesn’t mean you are safe. More are on the way. I like to harken time to the 4th dimensions theory that was mentioned above, which makes you wonder what it would be like to live in the 2nd dimension. But I digress. If we existed in the 4th dimension, then time would be an object to us that could be melded and formed, just like we meld and form matter in our dimension. ---
**Author:** ![MC\_Master\_of\_Ceremonies](https://avatars.discourse-cdn.com/v4/letter/m/bb73d2/32.png) [@MC\_Master\_of\_Ceremonies](https://boards.straightdope.com/u/MC_Master_of_Ceremonies)\ **Post date:** [December 15, 2003, 9:13pm UTC](https://boards.straightdope.com/t/whats-the-matter-time-travel-paradox/217938/22 "2003-12-15T21:13:44Z")
> [@](#): > > \*Originally posted by lissener \* > \*\*This just occurred to me, while watching the first Terminator on IFC this weekend. > > IF matter cannot be created or destroyed, then the total matter in the universe at any given moment is constant, right? What would the consequences of altering that constancy? > > If you send a Scharzenegger-sized chunk of matter out of the present and into the past, isn’t that matter now MISSING from the present and SURPLUS to the past? > > Is this proof that time travel is not possible, or can this “obstacle” be overcome? \*\* If we introduce special relativity we find that your statement isn’t strong enough, because a) mass is not a conserved quantity and b) There is no such thing as a “given moment” in the universe due to the failure of simultaneity. However within the confines of special relativity your statemnt can be altered so it still holds (i.e something along the lines that energy is always globally conserved in a given reference frame thus time travel is impossible) The problem arises when we go from the flat spacetime of special relativity into the curved spacetime of general relatvity and you now find that the new statement is no longer strong enough to rule out time travel if there exists closed timelike loops. At the moment there is no known way to completely rule out the possibilty of time travel as there are solutions to general relativity which contain closed timelike loops (even though those situations aren’t physical). [Previous page](https://boards.straightdope.com/t/whats-the-matter-time-travel-paradox/217938.md?page=1)