What’s the status of time travel?
Delayed.
Absolutely no progress has been made. Theoretical physicists think about time running backwards in their equations, perhaps to amuse themselves, wow the public, or they really think it might (or some combination). I would say: we don’t really know what time is. I have never read any physics in which it is more than just a parameter in an equation with no definition. I am convinced it never and can never run backwards. Not just for people, but also for any of the physicist’s postulated things that actually exist. I think I read that virtual particles are postulated by some to travel bacwards in time. I don’t believe virtual particles even exist in any sense, and they just help the equations, where the more accurate description would involve waves in an “ether”.
Well, since the OP was written, I’ve traveled into The Future! And it’s glorious! It’s everything we ever dreamed about.
Except for flying cars. Where are the flying cars?
I read an interesting book called, “The Science of Star Trek”, and an amazing number of things they do are actually possible if - and it’s a gigantic IF - you can generate enough power which, at this particular time, is way beyond anything we could possibly muster. However, the one thing that is impossible is the Transporter because of the Heisenberg Uncertainty Principle in Quantum Physics.
Time travel continues to remain in the realm of Science Fiction only.
Well, if there’s an aether, where is this aether? What is the nature of the aether? What’s it like? What is it made of?
The problem with the aether theory is that all the experiments made to investigate the aether instead showed that no such thing could exist. So there’s that.
David Brin invented a much more plausible version of the transporter in one of his short stories. It involves a chemical bath that separates every cell in the body into a slurry, the cellular slurry is then pumped down to the planet surface by long tubes, and reassembled at the new location.
The Uncertainty Principle is only a problem for a transporter if, for some reason, you restrict yourself to classical information channels. And even then, it might or might not be an insurmountable problem, depending on how much fidelity you need (which I don’t think is a settled question).
I find the argument “If time travel is possible, where are the time travellers?” not quite persuasive. It could be that time travel is expensive, uses considerable resources, and requires considerable time to accomplish, all of which would prevent casual time travel tourism.
Time to accomplish you say? It seems that most SF time travel assumes that the traveller remains in the same relative location on Earth. But all celetial bodies, including Earth, are in constant motion. If someone goes back 100 years, he/she would end up somewhere in outer space. So now he/she would have to take the time to travel to wherever Earth was at that point. And reverse that trip when he/she wanted to return. That simple logistic requirement could be enough to prevent any time travel from happening, even if its possible.
But where in space would you end up? If you say “where the Earth was located at that time” how would that spot be determined? Since there are no privileged reference frames isn’t any location relative? In the case of time travel, relative to what?
All very good questions! And they better be answered before we spend the expense and resources to send that spaceship back through time!
While a “Star Trek” style transporter would be difficult to say the least, there are well known and relative straightforward ways to accomplish the same goal.
We of 2018 are beginning to at least talk about emulating human brains in computers, and we’ve finally, after all these years, gotten artificial neural networks to function well enough to be useful.
We also, here in 2018, are beginning to approach the data densities needed to store a human brain’s entire neural connection map though we haven’t yet scanned one or gotten emulators to work at that scale.
But in theory, a transporter is pretty easy. You just send YourBrain.bin, a gigantic data file that contains the strengths, types, and connections for every synapse somewhere else. A machine at the destination receives the file. Appended to this bin file would be error correction data, quite a lot of it, so that the original binary file can be corrected for any transmission errors. Then, with technology we can describe though we are a long way from building, a machine at the destination would build a new brain (made of probably subunits made of artificial diamond) and a new artificial body (it probably wouldn’t bleed but maybe) for you to inhabit.
You wouldn’t need starships to go to any star more than once.
You’d need a starship to place the machinery and supplies at the destination first.
Yes, like walking.
When predicting the likelihood of future technology you need to count the “ifs” built into the statement.
A one if technology has a good chance of being achieved. A two if technology will result only if several improbable lines of research come together. A three if technology will never happen in Earth’s lifetime.
This appears to be a four if technology. Maybe five. Quite an achievement for a paragraph.
There are several ways around the paradox:
Backwards time travel that does not create a grandfather paradox creates a causal loop. The Novikov self-consistency principle expresses one view on how backwards time travel would be possible without the generation of paradoxes. According to this hypothesis, physics in or near closed timelike curves (time machines) can only be consistent with the universal laws of physics, and thus only self-consistent events can occur. Anything a time traveller does in the past must have been part of history all along, and the time traveller can never do anything to prevent the trip back in time from happening, since this would represent an inconsistency. Novikov et al. used the example given by physicist Joseph Polchinski for the grandfather paradox, of a billiard ball heading towards a time machine: the ball’s older self emerges from the time machine and strikes its younger self so its younger self never enters the time machine. Novikov et al. showed how this system can be solved in a self-consistent way which avoids the grandfather paradox, though it creates a causal loop.
Of course the computer you are writing this on was a five ‘if’ technology a hundred years ago.
I know that Novikov self-consistency is very popular among philosophers and physicists who contemplate time travel; but I don’t like it. It means that you could never kill Hitler, no matter how many times you try; this seems to deny any kind of voluntary agency on the part of the time traveller(s). Hitler would be constantly surrounded by a crowd of time travellers with jammed guns.
My idea is a five dimensional block universe; every possible timeline exists, including the ones that are created by time travellers changing history, but each time traveller experiences only one personal timeline.
…which may be the same idea expressed in a different way.
Nobody predicted it. And none of the technologies they did predict with multiple ifs ever came to pass.
Humans are very good at taking random advances and putting them together. They are very bad at the “if we only had ham we could have a ham and cheese sandwich if we only had cheese” wish fulfillment prophesies.
McCoy: Crazy way to travel, turning a man into soup!.
Brin HAD to be tongue in cheek. For the cost of the soupificator, the tubes (and stabilizing the tubes as they went down) and then the de-soupificator, you could just send a shuttle down to the surface.
Do you get left behind as the earth moves now? No? Maybe time travel would work the same way.
Who is to say than any time machine isn’t actually a space/time machine. However the travel works, it automatically compensates for the change in location. How? Who knows! But if you’re going to allow time travel stories, you have to accept that part. When (
) time travel becomes possible in the real world, we’ll know how to do that.
In the real world, a space/time machine is also a space machine. If I can travel back from 1985 to 1955 and stay in the same mall (and the machine automatically adjusts for the 117 B miles the earth has moved since then), why can’t it be used to travel .0000001 second into the past to a point 4 light years away?
The lack of known time travelers is not proof that time travel will never exist, but if it ever does exist you would think that at least one person would admit to it and be able to demonstrate they were from the future. Maybe they would realize nobody would believe them. However, there have been some things happen in the past that eerily presage future events (like The Wreck of The Titan). I wonder if anyone sold a million dollars’ worth of stock the day before Black Friday, or maybe bought as much Microsoft and Apple as they could right after the IPOs.