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Q & A: How to Travel Through Time

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Most recent answer: 10/09/2010
Q:
Are TIME TRAVELS possible? How?
- Utkarsh Pandey (age 13)
Haldwani,U.P,India
A:
Utkarsh -

That's a really good question. Unfortunately, nobody really knows the answer. There are people who think that time travel is possible, and there are people who think that it isn't. So far, no one has figured out how to do it. If you figure it out, though, I'm sure you would become very famous. :)

-Tamara

(published on 10/22/2007)

Follow-Up #1: Steady state universe? Probably not.

Q:
Doesenít theory say that there is a steady state universe and that you can neither create or destroy matter? So if you traveled thru time (forward or backward) would you not increase (or decrease) the total sum of matter in the universe at the points in time traveled to (and from) thus rendering the steady state universe theory wrong or at lease untrue)
- BJC
Illinois
A:
Many theories of the universe have been proposed.  A number are still in contention but the one involving a steady state is no longer considered consistent with modern observational data.  It was proposed in the 1950ís by Fred Hoyle and collaborators.  Our present universe is considered quite dynamic evolving from a big bang, star formation,  galaxy formation, cluster formation, and so on. As for creating matter/antimatter, well, actually you can at the expense of energy.  Itís energy that you cannot create or destroy. 
As for time travel, forget about it (except in science fiction stories).

LeeH

Some of these conservation laws get tricky for an infinite universe. What does it mean to say that an infinity has increased or decreased?

Mike W.

(published on 10/22/2007)

Follow-Up #2: information loss

Q:
Based on the Black Hole Paradox, as hypothesized by Stephen Hawking, everything in the universe contains information and that information can never be destroyed. If this is so, then can we not take information, store it in an energy-based medium, and then essentially recreate that information as it once was?
- Anonymous
USA
A:
This is problem of what happens to information is general, not specific to black holes. (Hawking for a while though that black holes were an exception to the rule that information is not destroyed.)

Of course we have many media in which we can store large amounts of information and then retrieve it. My current typing is being saved as magnetic patterns on several disks. The problem is that, according to the second law of thermodynamics, some of the information currently available will inevitably be lost. Yet according to the microscopic laws of physics (quantum Liouville theorem) no information is ever lost. So how do we reconcile these facts?

Here's a sketch of what is probably the current conventional wisdom on the topic. A lot of information is currently available as local organization of things. For example, the arrangement of dye molecules on a printed page is highly organized and obviously conveys useful information. Gradually that local information disappears (local entropy increases). It's replaced by a complex and largely inaccessible set of quantum entanglements between remote objects, e.g. hidden connections between the state of your mind and some imperceptible detail of the rotation of Jupiter.

We know of no way of reversing or stopping this decay of usable information.

Mike W.

For an amusing take on the issue see the article on the Thorne-Hawking-Preskill wager;


LeeH

(published on 10/09/2010)

Follow-up on this answer.