Or they know better than to visit the violent primitives.

nah, the reason is: when you travel back in time, our galaxy, solar system and planet are in different absolute universal positions. so you end up alone in deep space and by the time the planet reaches your position the time you traveled back has passed, making it absolutely useless and life threatening.

Maybe it's impossible to travel back in time?

Time travel within the same universe is not possible, it is a fun fiction which is always contradictory in some way. The only time travel possible would be the one that William Gibson uses in The Peripheral. His idea is that every time you go back in time a new parallel universe is created, and it doesn't impact your current universe because of that.

My theory is that we're one of the most advanced species in our galaxy, and yet we still can't reach another solar system. The probability of intelligent life forming from unintelligent life is extremely unlikely, and we had life on Earth for a LONG time before humans evolved. Intelligent life is very difficult to form, you need the perfect conditions and perfect stressors over millions of years. Then on top of that intelligent life which can reach another solar system is even less likely.

There's life out there thinking the same thing right now:

Or it's because we don't have time machines yet. It's like making a phone call when you have the only phone in existence.

I prefer the theory of "OMLY FORWARD!"

Basically, you can only travel forwards in time because going backwards violates causality

However

Because of the possible 4th dimensional geometry of the universe and what that means for how it behaves over deep time intervals, it could theoretically be possible to go so far forward you end up back in time.

This possibility relies on the accuracy of the theory of the bang and crunch cycle, which basically states that the universe is a bubble of infiniteness and that if you figure out how to ride out a big crunch and following big bang, you can just keep fast forwarding infinitely until random happenstance takes you far enough forward in time to a universe that is identical to ours except you're arriving to a point that is identical to one that was "back in time" from where you started.

It's probably one of the more depressing takes on time travel since it's impossible to ever go "home" but then again in that sense you've never returned to the home you left from in the morning, because the one you return to exists forward in time from where you left.

I believe the only viable timeline is the one where time travel is never invented because if you create the machine to go back to prevent something happening then there is no need to create the time machine.

Which yes is an actual paradox

The universe seems to be keyed to disallow time travel. The speed of light limit, in relativity, is sat exactly at the limit where time travel would become possible. Conversely, quantum mechanics does allow for FTP transmission. What it doesn't allow is information to flow along those links. It's hit with a 0.5 error rate, which completely blocks FTP communication.

General relativity does allow for a few time travel options. However, these are sat well off in the sticks, where quantum relativity would dominate. Since we don't have such a theory yet, our predictions are likely wrong. Even within these theories, a time machine would require a "closed timelike curve". These can, in theory be made using several rapidly rotating black holes. Any ship traversing it, would never be able to leave before the time machine was built.

Basically, time travel is almost certainly blocked by our laws of physics. Any loopholes would be limited to the lifetime of the "machine" and would require stellar level engineering for even a few seconds of travel.

Back to the Future had an extremely convoluted time travel theory that didn't actually make sense, but one interesting idea they sparked is that you create branching timelines when you go back to the past. Meaning your present timeline remains unaltered, but you basically skip to a new reality when you time travel. Essentially, they claimed the multiverse exists and you travel across dimensions, not necessarily time, when you used the Delorean.

Maybe this is why we never meet time travelers. Because our current universe is an unaltered world and any time traveling that happens here just sends people to other universes instead of our established timeline.

This theory is kind of nightmare fuel when you consider Doc and Marty left Marty's girlfriend on her porch in a dark future and just expected her to be there when they "fixed" the timeline. Nah, bro. You just abandoned her in the darkest timeline. The girl you picked up was an alternate reality version of her.

*EDIT: Back to the Future, not Bank to the Future.

Isn't there some theory that says the reasons why we don't see advanced civilization is because they destroy themselves with technology.

Or the timeline they are from is not our timeline

The future doesn't exist, and the past is inaccessible to our Temporality.

Or they're the things 99% of people are calling 'aliens.'

Why an interstellar species would travel light years to come to this pale blue dot in ships that don't really interfere and look like our own just a few hundred to thousand years more advanced is kind of hand waved away.

But if those sightings are in fact accurate, it sure seems like our narcissistic species would be pretty interested in our past selves once the tech existed.

If you were a historian with a time machine doing original research for your doctoral dissertation, you’d probably prioritize visiting the most poorly-documented eras first—the Information Age would be at the very bottom of your list.

There was an interesting physics paper recently that suggested that time travel was possible, but you wouldn’t be able to travel to before when the machine was built. Of course, it also would require an impossibly huge amount on energy, but that’s a problem for the engineers.

maybe they don't visit us because we never call or text

If time travel existed, why would anyone come to this time period where everything is fucked up?

And if the tech is regulated to stop altering the timeline, they could be here in disguise. Possibly literally invisible to us because they're only permitted to observe and not actually take part in anything. It could even be that time travel works like Paycheck and not The Time Machine, and you're just able to look into the future/past but not actual travel to it.

Or the branching timeline scenario in Back to the Future is the reality of things, so even if you went back in time to talk to yourself as a younger person, that happens in a totally different dimension than the one you were in when you yourself were a younger person.

Nah we've had them. We just lock them in mental hospitals.

Listen, the only logical conclusion to stop time tavel fuckery is a cascading series of event that cause all time travelers to be killed before tbey discover time teavel, or otherwise foil the discovery. The result is a nice clean timeline. I know this to be true because that technology would NOT be used responsibly

It takes more energy to go further back in time.

Everyone just assumes time travel is frictionless, but that doesn’t make sense. You want to go back ten seconds? Couple AA batteries. Want to go back an hour? Nuclear fission required. Seven days into the past? Microwave electronic resonance craft. A year? Forget about it.

I've begun thinking that time travel can only be possible if all of time were to exist simultaneously. Like a singularity. Then with complete knowledge and ability to influence matter you can rewrite time anyway you would like.

Like spreading the frames of a film out and altering them as you see fit.

If the Multiverse is a thing, then that timeline has happened somewhere and our future selves visited us. Ahahaha. That would be trippy.

In this Multiverse though, it looks like we become the Borg, so they would have already collected all the info they needed and thus have no need to go back in time.