The reason why we never meet time travelers is because our civilization ends before the technology can come to fruition.
The reason why we never meet time travelers is because our civilization ends before the technology can come to fruition.
Sort of similar to the Great Filter theory, but applied to time travel technology.
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.
Pretty sure there is no absolute universal position, everything in the universe being in motion relative to everything else as the universe expands, but that does not disprove your point anyways.
The reason it doesn’t disprove it is because the assumption “time travel works” is really just saying, if we ignore some basic rules of physics, what happens to what’s left? It’s a nonesense premise to debate what is basically nothing more than science fiction.
Could the rules we know about the universe be wrong? Absolutely! But discovering those new rules is what will answer that question. Till then, we might as well try and say Harry Potter is just quantum mechanics.
This is a basic fact overlooked by almost every time travel sci-fi. We wouldn't just jump into a machine and poof be in the exact same location 1,000 years ago.
It would be more like trying to land a spaceship on a planet light years away, there would have to be calculations for position and gravity. All sorts of crap before you even solve the impossible problem of turning back the clock.
Also we'd first have to figure out how to travel faster than light to even hope to break the riddle of time travel.
As fun as it is to theorize time travel would be impossibly complex and probably devastating to try.
Imagine what an object would do with all those forces behind it suddenly slamming into a object moving much slower, it would be like a time bullet that would tear apart the planet and punch a hole in space. We would likely achieve a black hole and destroy all of earth before we could see what earth looked like 1,000 years ago.
This is a basic fact overlooked by almost every time travel sci-fi. We wouldn’t just jump into a machine and poof be in the exact same location 1,000 years ago.
It would be more like trying to land a spaceship on a planet light years away, there would have to be calculations for position and gravity. All sorts of crap before you even solve the impossible problem of turning back the clock.
If the only reason you find the premise of traveling through time preposterous is that they didn't do the basic research to make it work, why not just assume they did? It's a fictional world. Just go with it.
The only theory I've seen that really holds any water is time travel going forward by using a ftl loop.
Have you noticed the flashing light in the sky? It started last year. It gets a little brighter every night. I only used to notice it when I was out of town, but now I can see it in the city. It blinks pretty quickly, probably twice a second. Some blinks are longer than others. If you watch long enough, it repeats. Short. Short. Short. Long. Long. Long. Short. Short. Short.
Maybe it's impossible to travel back in time?
If time travel is possible it'll probably be limited to the lifeline of the time machine itself. You cannot travel back in time to a point prior to the invention of the first time machine.
GR predicts "closed time-like curves," but they require weird conditions (an infinitely dense and infinitely long rotating string) or negative energy, and you can only ever travel to the start of the loop at the earliest.
No that can't possibly be the reason
Time isn’t really a thing, right? It’s just the chain of cause and effect, tied inexorably with space. There is only ever the present, the ever-shifting now. The past is a remembered state, the future is merely possible states.
Cause and effect happens more slowly or quickly due to relativity, but it doesn’t go backwards.
(Note, I am not a physicist.)
Location isn't really a thing right? It's just a chain of "over here" and "over there" tied inexorably with space. There is only ever "here", the place you occupy while things move around you. Behind is places you have been, forward is places you might be.
Reading that formed an interesting question in my (also non-physicist) mind:
If we can, at most, take advantage of relativity to slow down our own time frame, then time could just be our way to describe the pace of how space changes around us following simple causality.
But if, on the other hand, it is possible to move backwards through time, wouldn't the universe have to necessarily exist not only as a giant block of eternally changing 3D space, but as a giant block of 4D spacetime one could move around in? And would that mean predetermined past and future, or would that 4D block of spacetime change, too, advancing through meta-time, continually changing future and past of the universe?
ScienceClic has a cool video, stipulating that we live in 4D spacetime and are bound to always move forward at light speed. If we stand still in 3D space, we move forwards in time at light speed. If we accelerate in 3D space, we change out motion vector from only pointing forwards in time to pointing slightly sideways (up to completely sideways, i.e. time stops, if we were able to move at light speed). But there may be now way to do a 180 involving the time axis like we could do involving the other 3 axes.
Maybe they are afraid to come back because we are still savage cavemen and carewomen to them.
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:
One of my favourite theory about human evolution is the stoned ape theory. It delivers the conditions of the evolution. Apes were forced outside of the jungle and ventured into open field and had to depend on different nutrition. So they ate some mushrooms and eventually ate ones with psylocibin. Small amounts increase your eyesight - so you can hunt better, bigger amounts are very sexuall arrousing - so more reproduction :)
You don't even need that hypothetical for it to make sense. Look up how chimpanzees fight against each other for territory. It's survival of the fittest over millions of years, simple. Cold weather in the north, requiring the development of technology for survival, learning how to use fire to cook clean food, learning how to use alcohol to purify water, etc. We split from chimpanzees millions of years ago, and chimpanzees can only survive in very lush jungle areas because of the food sources they rely on, which is why they're endangered.
Time travel within the same universe is not possible
Not exactly true. Technically, paradox free time travel would theoretically be possible.
As long as the time travel follows the Novikov self-consistency principle, there's no need for parallel universes.
Essentially the type of time travel employed in Harry Potter and the Prisoner of Azkaban. So you wouldn't be able to change anything, even if you did do things — as if you did something, it had always already been done previously (before you travelled back).
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.
Imagine creating the first functional time machine only to have a shitton of time travelling tourists appear in it the second you turn it on
Exactly. We can still only send a single gel banana back in time until we invent proper time machines.
My favorite depiction of time travel tech is Primer. Assuming you figure out the time travel part itself, I can imagine a time machine that can take you all the way back to the moment it was switched on. Any other mechanism has introduces way more issues that time travel alone.
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.
There is a great Futurama episode that visualises this. The Late Philip J. Fry - Futurama S06E07
There's a hard sci-fi novel (1970s or 1980s) called "Tau Zero" that features this idea.
Book summary (spoils all of it)
A colony ship with a Bussard Ramjet on each end (debunked theoretical spaceship drive that uses interstellar hydrogen for propulsion, i.e. the faster you go, the more medium you hit and the harder you accelerate) suffers an accident that destroys the deceleration engine. They keep accelerating because they need the engine's magnetic field to protect them from interstellar dust. First they try reach the void between galaxies to safely repair the ship, when the interstellar medium is still too "dense," they go for the void between galaxy clusters, then superclusters, then they just stay on the throttle until the big crunch, at which point, in the nothingness after the universe collapsed in on itself, they can finally fix their ship and begin decelerating into the bounce-back big bang of the forming next universe and colonize a planet.
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
That's why the reason for inventing the time machine is "just in case"
Basically everytime you go back it will make changes to the future in such way you don't exist thus the time machine by its very nature can never be discovered. Everyone that does immediately erases their future self from existence.
I've never been motivated to create a time machine, but you've suddenly made it extremely appealing...
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.
As I understand, the FTL "transmission" in quantum entanglement is equivalent to just ripping a photograph in half, sticking the halves into envelopes and sending one of them to Australia.
By measuring the envelope you kept, i.e. opening it and seeing which half is in it, you gain instant knowledge, what the other half in Australia is.
This is mostly useless for communication, though, because the person in Australia does not get this information instantly.In the case of quantum entanglement, the photograph halves are a particle, which has decayed into two particles, each of which have kept a shared property, like a spin of -1 and +1 respectively.
This is the hidden-variables hypothesis and specific tests were made to check for it. See https://en.m.wikipedia.org/wiki/Bell's_theorem
Quantum mechanics does not allow for FTL transmission. Disallowing information flow is the same as disallowing transmission.
It seems to allow it, in a sense. The errors are also left on the transmission end. By transmitting them normally, the 2 signals can be combined to recreate the data. Something is shared, at some point.
It's definitely a "we're not sure what's actually going on" type situation though. Either both ends are drawing on some (otherwise) hidden data layer, or FTL transmission is allowed, so long as no information flows (information as defined by quantum mechanics). It just turns out that weird entanglement based systems are the only ones (we've found so far) able to send infomationless transmissions.
Both solutions would give deeper insights into reality, and its underpinnings. Unfortunately, we've not actually teased out which is happening.
My gut feeling is that the speed of light is a side effect of a fixed/stable causality across all rest frames. Hidden information seems to be a lot more cumbersome.
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.
Doc does draw that on the board, but the movie doesn't follow that logic. It's strictly a cause effect type of time travel.
The movie doesn't really follow they though. Otherwise why did Marty start disappearing.
That's why I said their time travel theory doesn't make sense. The movie doesn't even follow its own logic.
Or the timeline they are from is not our timeline
Isn't there some theory that says the reasons why we don't see advanced civilization is because they destroy themselves with technology.
Yep. Look up the Great Filter theory.
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 invincible has taught me anything, it's that the aliens are here because they want to fuck
Every civilization has its Captain Kirk.
maybe they don't visit us because we never call or text
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.
Future historians could have infinite time. We could get grad students a thousand years after time travel is invented. Of course, they could be sneaky.
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.
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.
Everyone is mentioning branching timeline of back to the future but the movie never follows that. Marty's parents are not getting together he ceases to exist. Biff brings book back and Marty goes right to that timeline. The movie is just cause and effect.
People bring it up because there is a scene in one of them where Doc Brown explains the branching timeline theory.
Or there are he boxes siting sound that we ignore.
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.
Seven days into the past? Microwave electronic resonance craft
I feel like that's a reference to a supremely underrated and long forgotten television show...
It’s a reference to a patent held by the navy. It’s concentric shells of nickel or something like that, then microwaves bounced inside that cavity. According to the patent it ends up producing power on the order of a hundred atom bombs per second.
Nah we've had them. We just lock them in mental hospitals.
Just tryna find the 12 monkeys bruv
Oops innit
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.
or it's impossible lol, today physics and teories agree that time travels to the past is impossible, it's go against literally everything, or ours theories are worng, but well it's working to this day
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.
Yeah but is there evidence to suggest that this is not the case? My understanding is that we don't really understand time.
I think, lots of people these days have an inflated understanding of time, because of the time travel trope in pop culture, as well as videos and simulations with time sliders being readily available.
Without getting into Einstein's theories for a moment, time is something we measure, we never modify time in reality.
In particular, we measure the progression of causality. Say, you kick a ball, then the atoms in your foot push the atoms in the ball, the whole ball rapidly accelerates and then takes 0.6 seconds to hit a wall.
You can't just set the whole process to -1x speed and expect it to happen in reverse. That breaks causality. The ball would need to fly towards your foot without anything giving it a push.
With our time sliders, this may seem like a small difference, but it's just completely different from anything we've ever observed in the universe.Now, about Einstein's theories, all of the above is still true. However, Einstein has discovered that travelling through time is possible, but only going forward in time, at a different speed than everything else.
Basically, causality has a speed limit, which happens to be the speed of light. (We believe photons to be massless, so with our usual acceleration formula, any acceleration would make them go at literally infinite speed. They don't, which is why a speed limit for causality is assumed.)
Gravity and your own speed can influence this speed of causality for you, meaning at a lower speed of causality, things happen less quickly for you and you'd age more slowly.
So, theoretically¹, you can get into an extremely fast spaceship, spend 5 years-as-perceived-by-you in there and then land on an Earth that's in the year 3000.
That is a one-way trip, though, because going backwards is not a thing.¹) In practice, you need to go at speeds for this, that are magnitudes higher than anything humanity has ever achieved.
also because it is genuinely impossible to move faster than light as matter, let alone survive it
That's why you make the space move around you instead.
https://en.m.wikipedia.org/wiki/Alcubierre_drive
That's not related to time travel though, but that's a link to an actual irl concept of a warp engine.
that's so cool
All those random scraps of metal you find lying are just the end result of someone trying to travel back in time and the time machine not surviving
The vulkan science proved time travel impossible
The Vulcan science directorate has determined that time travel is impossible.
Now I just wanna watch Primer again.
Incorrect. The child support liability on multiple timelines could no longer be insured.