Time paradox

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You can bring up as many examples of science being wrong as you like, but I'd bet anything that time travel is far too wacky to ever happen (other than pseudo time travel such as being frozen and waking up in a 100 years time).

 

God does play dice; my dearly departed great-great-great-great grandfather told me about a great game he had with God the other night.

 

As for Einstein, umm, quantum physics has actually discarded many of his theories. He's kind of like Freud. He was great in that he got us thinking about a lot of new stuff, but he usually turned out to be wrong.

 

Que? Einstein's theories were concerned with Relativity - Special and General. Whilst it is true that relativistic mechanics is not compatible with quantum mechanics, there is no way you can say that either SR or GR have been "discarded". They really deal with very different things to QM, which describes events on small scales rather than cosmic ones, as GR does. You could equally well argue that the problem was with QM not functioning at large distance scales. After all, it's definitely QM's problem that it predicts the Universe's wavefunction is time-independent, implying a steady-state cosmos when all experimental observations - and GR theory - contradict this.

And before anyone mentions the cosmological constant, even Einstein admitted that it was his "biggest mistake".

EDIT: and I even forgot to mention Einstein's QM papers! Well at least T2Bruno picked up the baton successfully. After all, it was that paper on the photoelectric effect that won him the Nobel prize, basically because the judges couldn't understand relativity...

[ March 27, 2006, 22:02: Message edited by: The Magpie ]

 

Umm... do you even know any of Einstein's work? Quantum physics was not accepted by the scientific community initially. Three major papers validated the quantum model -- two were written by Einstein. Einstein's interpretation of the photoelectric effect (which earned him the Nobel Prize in Physics) and his explaination of vibrational energy in crystals were monumental for quantum physics. Neils Bohr's model of the atom using quanta theory (where he explained every spectral line of hydrogen) was the third major paper. Quantum physics would not have been accepted by the scientific community without these theories.

I'm not sure where you come up with a statement like that. Einstein's work was the foundation of quantum physics. There have been many physicists who have expanded on Einstein's work, but the theories are still quite solid.

Edit: glad you approved, Magpie....

[ March 27, 2006, 22:15: Message edited by: T2Bruno ]

 

Ok, here's where I get my previous statement from. The names of the theories may still be the same, but the details of them have been so reworked and corrected over the past 65 years that they bear little resemblance to the originals. The same can actually be said for SR and GR. Einstein's predictions of what happens as one approaches the speed of light have been entirely rewritten.
Einstein also said that the time-space continuum is an unbreakable medium, meaning there can be no holes in it that haven't always been there. This idea is on the rocks, though M-theory may yet rescue it, of course M-theory is not concidered science by most scientists, simply because, at the moment at least, it is totally untestable.

EDIT: If this is right, then it means that the most probable form of time-travel, that of a temporal rift or wormhole, is out. The only other realistic theory is that we may find some kind of process that generates 'propulsion' in time, effectively letting us change our temporal velocity. Of course, if the laws of Newtonian physics still apply, that means we have to accelerate something else the opposite way (think rocket exhaust).

 

The "core" mathematics of GR is the same, it's only really the formulation that's different. Einstein formulated his original equations using Partial Differential Equations, which whilst the easiest way to understand what is actually going on, are too time-consuming to be put to use on solving more complicated problems. Hence, everyone uses tensor mathematics ( ) to solve GR problems nowadays, because it takes substantially less time, once you've got your head round all the bastard bastard bastard tensor notation. It's more the case that people have been building upon Einstein's original work rather than breaking it down. A lot of people have come along and used these new equations (which are really doing the same maths, but quicker) to unveil new cosmological insights, and add to our understanding of the large scale structure & motions of the Universe. It's like importing a file from M$ Word into OpenOffice, because .sxw files are smaller and load much quicker onto your PC than .doc files. You get the same text and the same formatting, but quicker and without having to sell your soul to Bill Gates. Similarly, you can still calculate the same planetary orbits in GR, but it will be much easier. If you understand tensors, that is...

No. Just... no. SR's description of what happens to massive particles at near-c velocities still stands. Any physics beyond that has yet to be tested. Besides which, any Grand Unified Theory will have the physics of both Relativity and QM as its basis, with new physics only really relevant in very high energy collisons. Just as Newtonian physics is entirely applicable to 99% of day-to-day physics problems. No civil or mechanical engineer uses QM or relativity, at least not in any even semi-serious way. The scientific method is not inductive - at its core lies falsification. A theory - any theory - is permanently "on probation"; when an experimental result occurs that contradicts the theory, then it becomes necessary to either ammend the theory or tighten up its field of applicability. It is very rare that a theory is ever "scrapped" completely. The process is one of constant progression, with no expectation of "absolute" truths, only useful ones.

This is how science is done. After all, if we just took what one person said as truth for all time and didn't improve upon it, it'd be religion.

 

I didn't know about the tensor mathematics. Thanks for clearing that up. Modern relativity has, however, discarded such notions as particles approaching the speed of light approach infinite mass and zero volume, and the reletivistic time thing is still up in the air.
As for the scientific process, I know how it works, but I think its safe to say that Freud was wrong about a lot of stuff. His theories are still taught today, and they were the origins of a great many modern techniques and theories, but Freudian psychologists are the laughing stock of the profession. Einstein was many, many steps above Freud, but the same general principle applies. He's been proven wrong many times, several of them in his own lifetime and he refused to admit he was wrong. A genius, no doubt, but a damn arrogant one.

 

Those are such excellent points that I can't believe I have never thought of them before. I hereby decalre time travel to be even more impossible than I previously thought.

 

Not true, these notions have not been discarded but rather have been expanded (and there is a big difference between the two). I've asked before which of Einstein theories have been proven wrong -- you still have not answered that question. You keep giving vague generalities that are not backed by any substance.

 

I'd just like to point out that 2 actually explains 1.

My own views on the subject are that the Timeline is self-protecting. Most travel backwards wouldn't work since you'd change something and the Universe would simply not allow it in order to prevent paradoxes. But forward (and any pre-determined backward) would definitely be possible. We even have a type of forward time travel available today: it's called cryogenics.

 

Now that is another damn good point!

 

Hmm... Not so sure about that one, Fel - the "Universe protecting itself" sounds a wee bit too metaphysical for my tastes. But there may be other explanations for time travel's impossibility.

Mostly, our arguments have been centred around relativistic mechanics, which is all well and good, as relativity does deal directly with time dilation and such matters. But it's also worth mentioning thermodynamics, and its connection with time via entropy and the 2nd law of Thermodynamics.

The 2nd law (or one formulation of it; there are many ways of expressing the same thing) states that: In a thermally isolated system, entropy must either increase or remain constant. All well and good, but it's not immediately obvious how that relates to time travel.

Entropy, for those who've not encountered the term before, is essentially a measure of disorder. The 2nd law can therefore be said to imply that as time goes on, disorder tends to increase. The caveat "in a thermally isolated system" is added to avoid confusion: whilst it maybe possible for disorder to be decreased locally, to do so would result in a compensatory increase in disorder in the surroundings.

Where the 2nd law gets interesting, however, is not in the banal study of ideal gases in tubs with plungers ( ), but when one begins to turn the statement on its head. If entropy increases as time shifts forwards, going "backwards" through time similarly would (theoretically) imply decreased entropy. But the 2nd law would proscribe this. It would seem that entropy is more than just an indicator of the amount of wiggling that atoms are doing, but also the direction that time is flowing. There seems to be a logical corollary between travel back in time and entropy decrease. Since entropy decrease is impossible, it follows that travel backwards in time is as well. The issue of the "thermally isolated system" does arise, of course, but it's a fair bet that any time machine would have to be considered "Thermally isolated" for the course of a journey back in time.

As for travel forwards in time, there are some "cheats" that enable you to do it, sort of. Cryogenics - whilst it's 99.99999...% that it's utter bollocks - could enable one to get a glimpse of the future (ta, Fel ), if it is medically possible to revive frozen corpses one day (personally, I'd bet that either it isn't, or no-one will be bothered ). There's also time dilation (i.e. the famous "Twin Paradox"), which would utilise time dilation to slow down your personal clock on a journey to near light-speed, before returning to Earth to see how everyone had got on in your absence. Theoretically achevable, accept that you'd need much, much more powerful rockets than are available today. And possibly more fuel than is left on the whole damn planet, too.

I think that a good way to think of time travel and entropy is as a free fall - you can tinker with how fast you're going down, but you can't go back up again. Of course, the analogy breaks down in trying to compare time machines to planes. Unlike fighting gravity, there just aren't any ways of making machines to let us completely reverse our plummet. At the end of the day, chaos always wins. Sorry chev.

 

Actually, the thermodynamics do bring up an interesting question: should time, in these instances be treated as a vector?
If so, then entropy always increases with forward motion in time, and decreases with backwards motion (or stays the same for either). If not, then we're screwed. Also, the closed system being the ship shouldn't matter. If the ship is closed, entropy will increase or stay constant in the ship, its the universe around the ship it's decreasing in. If the ship isn't closed, well, we get some interesting stuff.
Of course, if the ship is closed and entropy inside is increasing, then the ship must be going forwards in time, not back. You'd have to make time travel an isentropic event, and totally freeze everything on board.
The thing I have trouble with is that simple time travel means you have to pass through all intervening time. This means your ship doesn't just disapear, its always there, just time inside is different from outside. If someone crashes a car into you're time machine because you parked it where a superhighway will be (or was) then you're probably screwed. If a tornado passes through, the same. You see the problem.

 

That's a very good point, NOG, and one I'd considered myself. I can't see how it'd work in practice either, and I'm beginning to think that time travel is one of those concepts, like infinity, that whilst you can say it, that doesn't make it so.

 

If you have technology allowing you to travel back in time, you probably have technology allowing you to compensate for the motion of celestial bodies.

 

But not necessarily as matter. Take for example the Star Trek transporter; it converts your matter into energy before sending that energy to another location and converting it back into matter. The same could be done for theoretical time travel devices. Of course, even then you still have hazards (interference and the like), but not quite as solid as your examples.

It could be quite easily done if there were a 'receiver' on the other end (simple transmission), but then how do you get that there? You would need some sort of gravity source localization to fix coordinates on a particular celestial body, and that would require some sort of extratemporal sensor. Guessing just wouldn't cut it if the entire system/galaxy/universe is moving at unknown rates.