The Physics Of Back To The Future (Synopsis)

Mr. Strickland: “I noticed your band is on the roster for the dance auditions after school today. Why even bother, McFly? You don’t have a chance. You’re too much like your old man. No McFly ever amounted to anything in the history of Hill Valley!”
Marty McFly: “Yeah, well, history is gonna change.” -
Back To The Future

If you've ever wished you could go back in time and undo that mistake you made, to have a second chance to get it right the first time, you're certainly not alone. Indeed, for as long as the concept of time has been around, humans have dreamed about this possibility, as some of our oldest myths and stories involve traveling back in time to fix our own past, or even the pasts of our ancestors.

But from a physics point of view, this is likely impossible. Time travel is inevitable -- to the future -- but going to the past? That seems like much more fiction than science. While it's an entertaining fiction, Einstein's relativity in the Universe we have seems to prohibit it.

Image credit: New Scientist / John Papasian. Image credit: New Scientist / John Papasian.

Here's the science as to why!


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Very interesting and informative article. Distilled nicely for the layman.

Even if backward time travel were possible, it would seem to me a meaningless exercise, since one cannot remember the future.
You'd have no idea why you'd been sent then or for that matter what or who you are.

By Rick Shasha (not verified) on 22 Oct 2015 #permalink

Time travel into the future seems widely held as probable. I may be missing something here, but are we talking 'Back to the Future' type of time travel, or twin paradox time travel.

In the the twin paradox, for any single time frame, can it ever be said that one twin is in the future in comparison to the other? The twin is never in the future, only somewhere else.
It seems to me like being put into deep freeze is being interpreted to be time travel.
Is this any more time travel than we already experience every day?

Backward time travel is impossible because it is a logical impossibility.

1) Time is not a place. It is just our way of describing motion. One revolution of the Earth on its axis is one day or a complete ellipse around the sun is a year. If you could build a time machine, where exactly would you go? There is no "place" that exists in the passage of time.

2) There is no DVR recording the events of the universe. If somehow you could go back in time, there is no giant REWIND button that gets pressed and forces the universe to run backwards for your benefit. It's a logical impossibility for the entire universe to jump back into a previous state simply because you decide to go backwards in time, if that were possible, which it's not.

3) Almost every movie about time travel, including BTTF, forgets one critical fact about the universe. It is always in motion. Everything in the universe is constantly moving, including the earth. The earth travels approximately 50,000 miles every day in its circuit around the sun. So, if you went back in time one day in your Delorean time machine, and you instantaneously jumped from one time to the next without moving physically, you would find yourself floating in space! That's because the earth was 50,000 miles away yesterday, not having moved to where it will be today.

So, if you could build a time machine, which I have just shown to be impossible, but if you could, it would have to be capable of space travel. A Delorean just wouldn't cut it.

By Craig Iskowitz (not verified) on 22 Oct 2015 #permalink

Actually, that idea has been, in a form anyway, in the EE Smith Lensman series.

And in Piers Anthony "incarnations of immortality", Time, IIRC.

Geez, Ethan- you should've prefaced this story with, "SPOILER ALERT!" ;-)
(quick! go back and time and edit it to before I read it...)

Thanks, Ethan for putting this out near the anniversary of Back to the Future.

In your article you omit two factors.

One is that travel through the worm hole, according to mathematical modeling, is not possible because the tunnel, when formed, stretches much faster than anything traveling through it.

And, two, you do not mention parallel universes. If universes are arranged this way, then when you travel back in time (no saying how) via a parallel universe, and change things there, the first universe is not affected.

I'd like to hear your take on these comments, please.