Why don't we see concrete evidence of time travel?

[Num7]

If time travel to and from the past were possible... And if time travel to and from the future were possible... Wouldn't we see concrete evidence or traces of time travel?

Like remnants of time machines? I mean, sure, there are things like misplaced artifacts and strange helicopter hieroglyphics that come to mind. But shouldn't we be able to find remnants of time machines or other futuristic devices?

Or are we missing something? Something science doesn't want to see?

Maybe time travel doesn't work that way.

What do you think? Is the evidence all around us and we are not seeing it?

 

[Classicalfan626]

I'd agree with you that there is nothing in plain sight that is evidence of time travel beyond reasonable doubt.

But I do think time travel is very secretive, and any evidence that we can see is by no means beyond reasonable doubt. And if there's any concrete evidence of time travel that already exists, it's guaranteed to have been covered up by the powers that be. That's my overall gut feeling.

 

[Num7]

I agree that the powers that be probably don't want us to know that time travel is possible. It would open up so many possibilities, so many ways for them to lose their power over us...

I like that you suggest that time travel is very secretive. What if it is so secretive that there are literally organizations whose whole purpose is to clean up after time travelers who have left traces from their missions? That sounds pretty awesome.

 

[Darby]

The problem with the "it's a secret" proposition is that it is set to our current perspective. It's how we see the thinking of a would be time travel enabled society. The problem is "forever" is a long time. Once two-way time travel is invented all bets about secrecy are off. From "that" instant you have time traveling ability at all times going forward and into the past. What's the biggest secret the US has ever had? Arguably it was the Manhattan Program to develop and deploy a uranium/plutonium nuclear device. How long were we able to keep that a secret? Zero. General Groves took the entire R&D team to the middle of the desert, isolated them, put a fence around them and stationed military police to monitor them yet the secret was being leaked to the USSR during the entire program. In the case of time travel you have forever for just one time traveler to spill the beans.

I put scare quotes around "that" in "From 'that' instant..." because there is no possible way to identify the moment when time travel is invented. In fact there is no incentive to even try to invent time travel. Do we see anyone trying to invent boats today? Of course not. They were invented long ago. The same would be true of time travel with the exception that today's technology could have been invented in either the past or the future; it would be a technology that just is. Such a society wouldn't question the situation because it understands and is familiar with the implications. It seems to have never actually been invented. See Robert A. Heinlein's short story "All You Zombies..."

Once the secret is out you have forever for the technology, and all other associated technologies (electricity, metallurgy, solid state physics, special relativity, general relativity, quantum physics, etc.) to be leaked into the past. Again, forever is a very long time for hundreds of billions of people to further spill the beans. If two-way time travel is possible as we envision it why don't we have our own time machines? If two-way time travel is possible why are we still confined to Earth instead of exploring the galaxy? A time travel machine itself is sufficient to explore the galaxy. As Minkowski told Einstein, "From henceforth, space by itself, and time by itself, have vanished into the merest shadows and only a kind of blend of the two exists on its own right." Travel in space; travel in time. The choice is yours.

Why wasn't Hitler assassinated by a time traveler as a teenager? Why wasn't he saved by another time traveler? Assassinated again by a third time traveler? Saved by a fourth time traveler? Et sic in aeternum.

 

[Prez]

I think there could be several reasons.

1. No evidence left behind. Take for example, a device built using materials that melt. Mercury as an example, is a superconductor when solid--but melts at room temperature. A device using similar materials would just melt into the ground once it's turned off or disabled.
   • Assuming what I've been saying for a while is true, when a person travels--they're really leaving their universe behind. Thus, there would be no physical devices because they're constantly taking the evidence with them & we're just seeing the footprints.
   • Anyone with the technology and understanding would also take great care to cover their footsteps.
2. Evidence of traveling in ancient times would have been poorly recorded (if at all) as they wouldn't understand what was happening, nor would they have the vocabulary to fully explain.
   • A bit of modern technology in ancient times would cause them to write about gods and heroes.
3. Evidence in more modern times could be right in front of everyone. As Darby mentioned regarding Hitler--give people time travel and inevitably someone may try it. Then, realizing WW2 was the best possible outcome, others would step in to ensure the best outcome.
   • There would be many universes spawned, and the frame of reference from any given one may be hard to discern if / when / who / what was done.
   • People could encrypt future messages under the guise of fiction.
   • Technology we see and take advantage of today could have first been invented in a future alternate universe.
4. Evidence is deleted. In addition to the rogue travelers trying to off or save Hitler, others may step in to minimize damage (intentional or unintentional) and remove physical traces of devices--or just integrate those devices into their arsenals.
   • Spooks snatching people and their devices up falls under this category.
5. Evidence his hidden. This would be things like machines buried deep in the ground or ocean that can remain untouched for thousands of years. We're still finding tombs and cities even thousands of years later.

In general I think society could no more function as an everyday time travel society as it could a nuclear weapon society. Time / multiversal travel is a super weapon to end all super weapons, which the usage would be highly guarded.

Finally, I like Darby's other point about space. A device capable of moving through time must also move through space. Once you unlock the ability to go anywhere else, the probability of finding the physical devices on Earth at any one point in time grows exponentially smaller.

 

[Darby]

No evidence left behind. Take for example, a device built using materials that melt.

That's not the issue. The issue is having a commitment by an infinite number of people to keep a secret forever both in the future and the past. It's irrelevant that one person or a group of persons makes their gadgets from melting materials. It's that one person or a group that simply doesn't care to keep the secret or by some set of circumstances or omission lets the secret out of the bag. Again, they have forever for that one slip. Once that happens the game is over.

Take Titor for instance. He said he would not give away information that could be used to alter history. It was a secret and he was committed to keep the secret. Slick answer, yes? But the logical is irrevocably faulty. There weren't all that many people posting on the threads but there were a couple dozen people regularly posting.

Now, in the "Titor Posts" reality among the people posting with him is "Rick" who in the "No Titor" reality would otherwise have gone out with friends and met a woman who would become his wife instead of posting with Titor. But Titor did post and Rick chose to stay home and participate.

In the "No Titor" reality there is no Titor with whom Rick would post and he therefore goes out, meets and marries the woman and they have two children who grow to adult age and have two children each. The two children meet and marry someone and have two children each. Those four children also meet and marry someone and have two children each. At this point in the "No Titor" reality about 40 years have passed and there are already 14 people and four marriages that don't exist in the "Titor Posts" reality.

Next we go to Rick's spouse. In her "Titor Posts" reality she lives a completely different "No Rick" reality. She meets and marries someone other than Rick and after the same period of time, assuming two children per marriage, there are 14 people born. In this reality her children and grandchildren do not exist in the her "No Titor" reality.

The growth per generation is 2^n where n is the number of generation in the person's line. To get the total population you sum each generation into a single total.

It gets worse because this only accounts for Rick's and his "No Titor" spouse's line. It does not account for the sons and daughters in law's family lines in each reality. In each reality those children meet and marry people and create new realities that don't exist in the "Titor Posts" reality.

It's not 14 + 14 = 28, it is (14+ 14)^2 = 784 people who are divergent from the two realities after only ~40 years. We've now combined the two divergent realities. The next generation will be 784^2 = 614,656 (round it to 614,000 because at these numbers not everyone has survived). At this point we're only ~60 years down the pike. One more generation, 80 years and not a single on earth in either reality would match the expectation value one might have had in 2000. 614,000^2 is ~377 billion people (obviously far, far, far more people than have every existed since the earth formed).

And this only considers Rick. It does not consider any other person who was posting with Titor on this site and/or Post-2-Post.

In less than a century history has spun out of control (at least for the omnicient who can "look down" and see the different permutations). All because Titor appeared and said, "Shhhhh....it's all a secret and I refuse to tell you the secret because that would alter the 'timeline' which is a big no-no even though I'm mavericking this visit without authorization because I want to have fun, drink orange wine and get drunk while posting on a public BBS...and my handlers will never know." His handlers, at least the ones he knew, likely no longer exist. The fact that a time traveler appeared at all alters reality.

See Ray Bradbury's short story, "A Sound of Thunder" for details.

In short, the situation created by a Titor would-be time traveler is called a boundary condition. The future evolution of a system is, in principle, determined by the initial boundary conditions of the system.

 

[Prez]

I like where your heads at, Darby. Language easy enough for me to understand ^_^
What you've described is indeed a boundary condition. You're also correct in your assumption regarding the future evolution of a system intrinsically tied to its initial conditions, which all discussions would be relative to w/e "it" is. The scenario you laid out is a good extreme example, but still within potential probabilities. All still within the realm of a layer 1 multiverse.

What really seems to cook people's noodles are infinity, and how not all infinities are the same or share the same cardinality. Superpositions and probabilities play into exactly what you described. A similar boundary can be found by taking the opposite assumption, that non-titors are maidenless & would not have procreated (effectively zero'ing them out in the calcluations). Between those two boundaries, you can probably guess, is infinity again.

You also lightly touch on the Ripple Effect (or butterfly effect w/e you want to call it). I like the ripple analogy because they're effectively circles that grow from the origin.

Again, they have forever for that one slip. Once that happens the game is over.

Feels like something people have been saying for years. The multiverse is uncountably infinitely stacked against travelers, yet people still want to change things. Many reasons why not to change anything, or why one should take every effort to minimize their impact, but never as much discussion on how quickly even a small change (I used punching Presidents as an example in a different post) can quickly ripple into extreme levels of divergence when someone metaphorically "re-nocks" time arrows & fires them off with different trajectories.

Still not impossible, just highly improbable (for good reasons!)

Some more thought experiments:
-If Rick posted frequently on TTI and missed out on wife and kids because of Titor, how would anyone know & does it mean anything if nobody knows? Wife, kid, and grandkids would all be in superposition relative to Rick so he wouldn't even know. Takes at least a third observer to resolve a dispute between two people disagreeing on something. Rick would be in superposition to all TTI members unless they engaged.

-If you have a thought and do not write it down, can it be said that the thought is "real?" If you remember to write the thought down, is it any more or less real than the first thought? A thought transcribed on some medium can potentially be considered "realer" than a thought by itself. I propose the thought transcribed has greater "weight" or "realness" to it than those that remain as thoughts.

Similarly, our interactions here on TTI can have different weights that would need to be factored in as well. As an example, I would wager mine are a bit weightier than say, a guy who wants you to send him $5mil in bitcoin to build a time machine in like 20 years no guarantees. All of which if we start factoring in events outside of TTI...the weight diminishes significantly. A lot of messiness can potentially be avoided by zeroing out trivialities and dealing with the margin of error.