Well, it is interesting to imagine what the universe might look like if time travel was possible, and easy. If time travel is invented in the future, would the people of the future (either humans or aliens, or both) come back in time to colonise the present and the past? A universe with time travel would make the Fermi Paradox look simple.
According to the ideas/beliefs of Erich Von Daniken and the like, our species was genetically engineered by aliens in the past. According to the beliefs of others, there is no life on other planets due to the exceedingly slim chances of evolution occurring. So, if you want to weld these two beliefs together, you get the idea that we were actually genetically engineered by time travellers from our future.
Which, honestly, isn’t a legitimate, scientifically-based “method” at all (as you asked about in your OP), it’s just the premise of a science-fiction story.
I don’t think that’s necessarily a valid argument against time travel. Why not assume we could also travel in space as well?
Or what if we invent one of those machines in Tenet that reverses time for whatever you stick in it? You would still be moving relative to the Earth, except that everyone around you would appear to be travelling in reverse.
But the big problem I have with time travel (aside from all the causality issues) is that it’s never really clear to me WHERE the past actually “is” relative to my present frame of reference or why my particular present should be considered more or less important than that point in the past.
Like if there is a distinct past that exists, then there is a distinct future. So all of history essentially becomes like slides on a movie reel. A lot of fiction posits that is, in fact, how time travel would work and that you would not be able to alter the past of future. But it can also lead to bootstrap paradoxes where objects don’t have a point of origin in history. Like the inventor of time travel being handed blueprints for building his time machine by someone from the future.
Why have we not reached Mars then? Or Titan, for example? Because the are far away. Even if we could travel there we would need an enormous machine to take us there: a rocket. Now the time travel is supposed to happen, without the machine, but with the transportation solved?
OK, imagine for the sake of the argument you can do that. So you apparate Harry Potter style on the surface of Earth. If you apparate below the surface, you are dead. But if you apparate in the air, what happens to you (or any other object) when the air that was there is now suddenly inside you? In my case that would be around 80 liters of N2 and 20 liters of O2. I fear I would be literally torn apart and explode. There is something everywhere on Earth: how do you make it go away so there is space free for your body?
And you not only have to apparate at the right place in the right moment, but at the right speed also. Otherwise you are going to splat against that wall, or that mountain slope, or the ground itself that is coming towards you at a significant fraction of the speed of sound relative to your speed.
Perhaps I lack imagination, but I don’t see how this is going to end well for you.
Any method of ‘time travel’ that goes outside of your subjective light cone is by definition “faster than light” travel, and vice versa.
This isn’t a reason that time travel cannot exist but it is certainly a complication for anyone who thinks they can just travel “in time” without reference to movement “in space”, or to exit a path at any arbitrary location in spacetime that isn’t a predetermined locus. A similar problem exists for the arbitrary teleportation of matter a la the “transporter” of Star Trek notwithstanding the fundamental impossibility of being able to disassemble a living organism in one location and reassemble it in a remote location in an identical and still functional form.
Stranger
Von Daniken is a crank whose crackpot speculations have zero scientific basis.
Has anyone quantified what those “exceedingly slim chances” actually are? Given that the JWST is discovering complex carbon-based molecules around distant stars and compounds consistent with life in the atmospheres of exoplanets, the odds may actually be pretty damn high on any planet with the right conditions. And even if the odds were a million to one, that’s still a virtual certainty that life will occur throughout our galaxy and all the other galaxies beyond.
It’s at this point that I’ll mention I actually did know someone at one time who claimed to have discovered the secret of time travel. His name was David H.Boyle. He was the guy responsible for running the Doctor Who and Conspiracy Theories exhibition at Blackpool. He’s since died from a stroke. He believed our species to have been genetically engineered from a lion and an ape, and according to him the Sphinx at Egypt represented said lion. He also claimed to have had encounters with extraterrestrial life, and also to have travelled back in time to the era of the dinosaurs (when he actually encountered one he was protected from being eaten by a "guardian angel’, or so he said). Other unusual beliefs held by him were that the Earth was 40 billion years old instead of the 4.6 billion years scientists usually estimate it’s age as. Also, he believes our species to have been around for hundreds of millions of years, which again contradicts the teachings of science which say we’ve only been here merely for hundreds of thousands of years. As far as religion went, he seemed to be pseudo-, atheistic, preferring to use the term “consciousness” rather than God when referring to the being that was responsible for creating the universe.
Too bad your friend is dead, I’d love to ask him to explain how come the sun, given its mass, is still burning brightly in its main sequence stage after 40 billion years. I won’t complicate the matter with any sort of questions about the known age of the universe.
His other beliefs, such as that we were genetically engineered by aliens from a lion and an ape, and that he traveled back in time to the era of the dinosaurs protected by a guardian angel, are more reasonable and I would have liked to subscribe to his newsletter. Speaking of the Sphinx, Woody Allen once wrote a history of mythology that included an account of a mythical creature that had the head of a lion and the body of a lion, but not the same lion.
The origin of life has nothing to do with evolution.
IMO, whether or not time travel is possible may depend on how you define it.
Certainly, being able to see events in the past would be possible if you can travel faster than light and have a powerful enough telescope - you have to travel to a point where the light from the time period you wish to view is just about to reach it.
On the other hand, in terms of being able to be present in the past/future, I think the closest we can get is relativistic aging - someone traveling fast eough long enough can, in effect. travel forward into the future. However, going into the past using known forms of physics and mathematics is impossible, for one simple reason; even if time is treated as a dimension in space-time, then you can’t go from space-time point A to point B without passing through a continuous series of points between them, and trying to go back in time at all will have the same result as trying to walk through a wall - you’re going to run into something that stops you. In the case of time, the thing you run into is yourself, a billionth of a second ago.
Stephen Hawking famously cited the fact that we had not been invaded by tourists from the future as evidence that time travel would never be possible and would always remain in the domain of science fiction.
However, how does he know that the U.F.O.'s we are supposed to have encountered are not piloted by the very time travellers from the future he believed to be an impossibility?
P.S. Travelling backwards in time within one’s own universe may be impossible but, as I’ve mentioned previously, how do we know there aren’t parallel universes we could enter where our past is their present? And another thing, wasn’t John Logie Baird initially thought to be a lunatic when he claimed to have invented television?
Here’s the David H.Boyle I mentioned in a recent post:
For that matter is there necessarily only one past? As in, if different possible pasts could converge on an identical present, then you could only postulate more probable versus less probable pasts, not one absolutely certain past.
For those who remember the 1970s Saturday morning show Land of the Lost, I think something like that might be necessary for time travel: an artificial bubble universe which can shift when and where it connects with our universe.
Will someone please build me a TARDIS pretty soon, I’m getting desperate? Simply gotta travel back in time and speak to my mum and dad. Gotta tell them about everything my future has in store for me.
To my knowledge, nobody has ever traveled from the future to the past. That is, there has never been a credible report of someone who claimed to be from the future and (for example) provided evidence in the form of very detailed predictions of events in our future. For example, if someone in the summer of 2001 predicted the events of 9/11 in excruciating detail - the exact times and locations of the aircraft impacts, building collapses, and names of the ~3000 fatalities - and got their report logged into official records before those events happened, we might start to take the possibility of into-the-past time travel seriously.
The fact that we’ve never seen such a thing (not just related to 9/11, but to any historic event where the reported details aren’t the kind of thing anyone could know in advance) could have two causes:
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Either time travel into the past is truly impossible, or
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Time travel is possible, but humanity is utterly destroyed in the near future. This must happen in the near future (before we learn how to time-travel), and it must be an event that ends humanity so that we never learn how to time-travel - because if we ever learned how to time-travel at any point in the future, then there would be a very long future full of time travelers coming to the past, and eventually one or more of them would show up during our lifetime.
(if there’s concern about a time-traveler’s report affecting the reported events, then we’d want a report of natural phenomenon that we don’t have the power to change, e.g. earthquakes, tsunamis, hurricanes, volcanic eruptions, solar storms).
The type of travel into the future you are describing is different than the instantaneous time jump imagined in science fiction. We are all traveling into the future, all the time. The trick is for you to travel into the future at a different rate relative to someone in a different frame of reference, which can theoretically be done to a significant degree if you can travel through space really really fast. It doesn’t have to be near the speed of light, but the closer you get, the bigger the difference in rate.
Also, using this method it’s a bit of a bummer that you can’t go back again.
If I lived in the future and could freely travel into the past, I would do a lot more than just anonymously buzz Air Force jets and hover over cow pastures.
It’s no wonder he had a stroke.