Can time travel happen, even if it’s a century from now?

By Chris Craddock

I originally wrote: “No. Nobody can convince you that time travel can happen because it really can’t happen. Not in the sci-fi sense everybody seems to long for.

We are all “traveling” forwards into the future at an eye popping rate of 1 second per second. We can’t go forwards any faster than that and we can’t EVER go backwards in time. Bottom line, time travel isn’t possible.

Then David Chidakel asked “I would like to hear your reasoning”. I started to answer David in the comment section but my answer got quite long, so I decided to edit my original post instead. I have written a few answers about this topic already and this one might end up TL;DR but what the heck, Here goes.

Time’s arrow…
Some physics equations seem not to care about the sign of the time variable, or in many cases not to care about time at all. If you suspend disbelief for a moment, they seem to allow for “closed time-like curves” and quantum entanglements which is geek code for “time travel”. But those are only hypothetical quantum scale effects. They probably don’t work out when considered in conjunction with other known physical laws and certainly don’t work for massive objects like people and time machines.

First of all, let’s dispose with time travel into the past… that is ruled out by thermodynamics.

First (law): just for grins and giggles let’s assume a time lord has invented a blue box that somehow instantaneously leaps the traveler back to some particular time and place in the past (relative to the traveler’s rest frame yada yada) where/when the travelers step out of the box and start interacting with the universe and alien creatures as they were back then.

But atoms/subatomic particles and their constituent energy fields are pretty tough things. They might get smashed in an accelerator or reactor, or be fused inside a star or have their electrons torn off inside a 9v battery along the way, but for the most part they are eternal and indestructible. Certainly within your own lifetime your atoms belong to you and only to you.

The problem then is that  instantly upon arrival all of the atoms making up the traveler and his/her time machine would suddenly have to exist in two places at the same time: Inside the traveler (obviously) and ALSO inside  whatever those same atoms happened to be contained within at that exact moment in the past. That can’t happen. If it could the whole edifice of physical laws would fall apart. So strike one.

Second (law): a.k.a. “entropy always wins”. The universe is made up of atoms/energy fields each more or less randomly going about its business. At any given moment we can’t even know everything there is to know (position, momentum etc) about a single atom (according to Heisenberg and half a dozen other quantum laws) -AND EVEN WORSE- a moment later even that information is lost.

So no matter how much energy you’re willing to expend, there is simply NO way to rearrange all of the particles in the universe back to some prior state. The information about that state doesn’t I have written a few answers about this topic already and this one might end up TL;DR but what the heck, Here goes.I have written a few answers about this topic already and this one might end up TL;DR but what the heck, Here goes.exist. Fried eggs can’t become fresh unbroken eggs no matter what you do. So even if you can decide “when” to go back to, there is no “there” to go back to. Strike two.

Third (admittedly just a thought experiment): While we know that time and space are entangled from a relativistic point of view, they are not the same thing. If time was just another dimension that you could (somehow) independently move along like a bead on a wire, then perhaps you could just pop out of the blue box and the universe would be sitting there exactly as it was “before”.

But whose version of “before” are we talking about? There is no universal time reference. That line of reasoning leads to grandfather paradoxes and infinite regression. If we supposed for a moment that it could happen, how could you ever tell? Aside from the violent anti-matter annihilation of the travelers atoms 🙂 I imagine the rest of the universe would simply carry on exactly the way it did last time. So logically it can’t happen. Strike three.

Now let’s think about time travel to the future. This also fails the thought experiment above.

The Future
Now let’s think about time travel to the future. This also fails the thought experiment above. In gross details if we look at (say) a tennis ball in motion right now and we know its position and velocity and mass and angular momentum and air density etc, we can predict its future position quite accurately for a short time O(seconds). Beyond that, we just can’t predict its future. What happens to the ball next week, or in a hundred years from now? How about the position and momentum of every atom in a nearby star or the couple of hundred billion of its cousins in our galaxy?

Time travel to the future isn’t possible because the future has not happened yet. Which future would be traveling to? Our blue box can’t slide the travelers time bead along the wire of the time axis because we just proved (above) that there IS no wire. And the blue box can’t rearrange the entire universe’s atoms into some as yet unseen future state because it can’t predict what that state will be, even if it had the means to rearrange them to its desired state.

3 thoughts on “Can time travel happen, even if it’s a century from now?

Add yours

  1. Time travel, as it is known, is mostly a literary plot mechanism, and a horribly overused and tired one at that (see Star Trek reboots). I say this even as a nearing 40-year fan of that blue box time traveler. As far as contemporary fiction goes, time travel is the refuge of the lazy author.

    This post mentions my favorite argument against travelling into the past, that the same objects/matter/atoms cannot exist twice or more in the universe at the same time. It’s a great example of a negative proof.

    On time being constant and travelling into the future, I’m not so sure, because here I think of Einstein. According to him, time is relative for us all, such that we are all “time travelling” based on our relative speeds. It is obviously entirely academic for us until you near the speed of light. And of course, we can only travel into the future, insofar as our relative time may slow down relative to those slower-moving people around us.

    Although I feel pretty confident in these past/future time travel assertions, I am not so arrogant as to not acknowledge that someday even all this can be unproven by advanced thinking. Perhaps, a century from now, an entirely new field of quantum mechanics will show how travelling into the past could work. There may even be theories explaining the universe that ignore entirely the time variable. How cool would that be? But it’s all beyond my imagination for now.

    Liked by 1 person

    1. To date, the most in-depth comment to any article I’ve posted on this newly-created blog. I thank you for that. I also agree that according to Einstein’s conjecture, time travel is indeed possible, a subject, perhaps, for a future article. It is relative to whom is observing, and that is why it is interwoven as spacetime. For a man traveling at near the speed of light, looking back at earth, people would appear to accelerate. Thus on his return to earth, the people will have grown older than he, thus indicated he traveled forward in time.

      There is an interesting article posted at entitled Einstein’s Relativity and Everyday Life by Clifford M. Will. In this article Mr. Will points out the very ordinary influence time travel has on each and everyone with a GPS device like a smartphone. Since GPS satellites are traveling in orbit around the earth, their built-in time is traveling at a different speed than we here on earth. If this is not compensated, it would throw the entire GPS system off by as much as 10 km per day. This is an astounding figure that proves relativistic time travel affects everyone.

      Liked by 1 person

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