I could have posted this in GD as a science question. Science fiction certainly has done it to death. But I thought it would be more fun to post it as an opinion poll. I’m serious.
Will faster-than-light velocity and time travel ever be possible? It’s presented as one question. But answer ‘yes’ if you think either one will be possible some day, I mean in human history. And please, please give your reason or reasons why.
Me, I think of course it will be. Just a couple hundred years ago people thought human flight was impossible. And need I say more?
Of course my answer is very unscientific. I’m guessing you will provide better and more qualified answers.
Thank you in advance for your kindly and civil replies:).
It was not a law of physics that flight was impossible. It is a law of physics that FTL travel is impossible. That’s just the way it’s set up, there’s not some physics cop out there who will give you a ticket for FTL.
Time travel into the past specifically is prohibited.
Time travel into the future via time dilation is certainly doable-in fact technically astronauts have been doing it for decades, and heck the entire human race/planet really.
If time travel into the past were possible, we would have already seen some from-the-future people making appearances in our current day by now. Or some inexplicable futuristic person having shown up in ancient Babylon.
Yes as a way of getting from point A to B faster then light can unquestionably yes. God didn’t leave us hear to die, there is a way. Now drag racing a photon, no I think we will have a work around that obeys the laws, not a power through breaking the laws to accomplish this. Time travel I believe will come however only when we are ready, which is further off.
This effectively invokes parallel universes to avoid the grandfather paradox. Perhaps this is not satisfactory, does not comport with what we think of as “real” time travel; but perhaps reality just doesn’t work the way we intuitively think it does, and time travel would make the quantum mechanical principles under which reality operates more apparent.
It’s not an issue of whether they will be possible someday. The physical laws of the universe don’t change. Faster-than-light travel and time travel are either possible or they aren’t.
Our current knowledge of the physical laws of the universe says that faster-then-light travel and time travel are not possible.
To be clear, the question “will it someday be possible” is really the same question as “is it possible now”. Human flight is possible now. Centuries or millennia ago, human flight was also possible. It hadn’t been done yet, and it would have been very difficult to do, but it was possible.
With time travel, the objection isn’t that we don’t know how to do it, or that we don’t have enough energy available, or that it would be impractical. The objection is that the Universe simply doesn’t work that way. Now, is our understanding of the Universe complete? Certainly not. Is it possible that there’s some loophole in the laws that we just don’t know of yet that would allow for time travel? It’s conceivable. But that’s not the way to bet.
In fact, they are separately conserved. Those two laws are just as ironclad now as they ever have been. We’ve simply found some cases where those laws are not manifested as intuitively as we might like.
It is important to be precise when addressing laws of physics. It is true that an object with mass cannot obtain a velocity greater than c = 299 792 458 meters per second. The reason for this is due to invariance of the propagation of energy through space and the famous mass-energy relation, and all that special relativity entails. (I would caution against assuming that special relativity is actually a scientific law because while it does improve upon Newtonian mechanics it, too, is likely an approximation of a deeper mechanism for how the physics works at a fundamental level.) However, there are a number of theoretical ways to travel from one point in space to another point as measured in a reference frame that are beyond each others light cones, including the controlled distortion of spacetime (a.k.a. a space ‘warp’ drive like the hypothetical Alcubierre drive), creating or using multiply connected manifolds (traversable wormholes), exiting and reentering the universe via some ‘outside’ space (‘hyperspace’), traveling along some compactified spacial dimension that is much shorter than the normal three spacial dimensions we observe (a ‘jump’ drive), or transferring information via nonlocal connections (quantum teleportation).
Are any of these likely to be practicable? It seems unlikely at best given current understanding of physics; even those that have a firm theoretical underpinning such as traversable wormholes or the Alcubierre drive require some kind of ability to manipulate spacetime directly with much finer control than you could have by just moving ordinary mass around (so-called ‘exotic matter’ or negative energy particles), and the energies required are literally astronomical. Others, like “hyperspace” or “warp” drives, are really just a literary conceit of science fiction writers to facilitate an interstellar story that can occur over reasonable timespans. However, two hundred years ago, electricity and magnetism were two separate natural phenomena that were a curiosity, and the maximum amount of power that could be artificially produced was measured in the output of beasts of burden. The integration and subsequent application of electrodynamics fundamentally altered our society and our planet in ways that people before simply could not imagine, and a single individual can operate a vehicle that moves at speeds or flies through the air in ways that are literally inconceivable to someone of the pre-Industrial world. An analogous revolution in physics that would allow the direct manipulation of subnuclear particles they way we manipulate electrons and photons today may allow access to energies many magnitudes of order greater than we can imagine today.
As for controlled time travel, there are again many theoretical possibilities to create closed timelike curves which allow you to follow a path that can put you outside of your light sphere into a past temporal direction, and frankly if you had some form of apparently faster-than-light travel listed above, you would also have a time travel device of sorts albeit not one that would not likely have you zipping back to historical events disguised as a police telephone box. There are, again, a number of reasons to believe that these would not be practicable even though it can be modeled within conventional physics, so it seems unlikely that practical travel back into the past is possible (and certainly not to a past prior to having invented your time travel gadget). However, we cannot rule out that some radical new revelation in physics could permit an ability to travel backward through time in a spacelike fashion, although doing so would definitely break physics as we know it, including problems fundamental assumptions such as causality and conservation of energy.
So, the only real answer that can be provided is “We don’t know.” But if it is possible, it will require some fundamentally new understanding of how the world works, not just smashing some matter and antimatter together, or somehow getting a DeLoreon up to the improbable speed of 88 miles and hour while dumping 1.21 GW through a “flux capacitor”.
The argument that I usually hear, is maybe they are here;), just well-disguised. Granted it’s usually the nuts who offer a pseudoscience reason for that. But you have to consider every argument, no matter how outlandish.
EDIT: BTW Star Trek: TNG even did a show on this subject (I forget the name offhand). A historian from the future came to the Enterprise. He didn’t do a very good job of disguising himself. But he was later found out to be a fraud (which actually brings up another good point).
And even 10000 years ago, it was provable that heavier-than-air flight was possible, as demonstrated by the fact that birds exist and most of them routinely engage in heavier-than-air flight. Making machines that do what birds already did (and having enough additional capacity to carry a human along with) was always known to be an engineering, rather than a “law of physics” problem.
Conversely, there are no “faster than light” birds puttering about, making it obvious that human FTL is possible if we just figure out how.
There’s no question that up until the end of the 18th century, most educated people who wrote about the subject doubted that humans would ever fly. A few speculated about emulating birds, despite Icarus, but none gave any reasonable pathway to flight.
Hot-air balloons proved them wrong in one sense. People could get themselves off the ground, although they were then at the mercy of the winds. People died because of this.
After that people started defining “flight” as heavier-than-air craft that were controllable by their pilots. This was still generally considered impossible. The modern understanding of progress in the sense that invention would always bring better results and new inventions would make the previously impossible possible developed slowly as the Industrial Revolution spread. You can catch glimpses of this attitude after the U.S. Civil War but it wasn’t widespread until the beginning of the 20th century.
Not only did most people not believe that heavier-than-air controlled flight was possible in the early 1900s, they flatly refused to believe that the Wright Brothers had succeeded at it (especially in Europe). They had been hearing for decades that this guy or that invented a contraption that flew but every time somebody tried to demonstrate it in public they failed. Prevailing thought wasn’t that inventors were getting closer and closer and would inevitably fly, but that it was a load of foolishness that everybody knew was impossible. Not until the Wrights finally made a series of public demonstrations in 1908 did public opinion change. After that, all things were possible. No one dared say that any claim was inherently impossible; they would get shouted down and accused of insufficient faith in modern technology. It was that thinking that led to the rise of science fiction and a capital “F” Future of technological wonderment.
Since until the advent of lightweight yet powerful gasoline engines no power source known at the time could lift a craft through the skies to an arranged destination, the mid-century doubters were more correct than the dreamers. Their error was one of engineering, not basic physics.
There are physicists who claim that a form of time travel is possible within known current laws of physics, although they involve things we haven’t proven to exist, like wormholes and infinitely strong materials. You can claim these are mere engineering obstacles that we can overcome but for the moment such a claim has no meaning. Besides, when people talk about time travel they mean - analogously to flight - that it must be controllable: you journey to a set destination and return to your starting point. Anything else is hand-waving. The concepts of FTL and time travel, again like flight, are social concepts more than physical ones.
Whatever physicists learn in the future, my feeling is that the social concepts are impossible. The universe is bigger and deeper than we are.
