Time Travel

[swainy (tc)]

But Ok, hows this for a physical limitation?

Obviously, it's not. Been there, done that. Read your own article.

Not sure what this has to do with time travel, though

It has everything to do with never giving up. To reach our goals. And understanding, nothing is imposable. We can work out how, and we will.

tc

[Chris Peterson]

It has everything to do with never giving up. To reach our goals. And understanding, nothing is imposable. We can work out how, and we will.

There are things that are truly limited by physics. Such as how fast you can go. There are things that are impossible. You can spend forever trying to get around natural laws, and it still won't happen. One of the truly important things that comes with a deep understanding of something is the knowledge of what is possible, and therefore worth trying for (despite what might be great practical difficulties), and what is not possible, and therefore should not have time wasted on it.

[Guest]

obviosly mark is not so good with 'right' examples of physical limitations that were overcomed. better examples would be indivisibility of matter, then indivisibility of atoms, then indivisibility of particles, currently indivisibility of quarks... just because we are out of resources to go any deeper that way, doesn't mean there's nowhere to go in principle. and if we could go there, who knows what kind of physical forces we might find, and what would be macroscopic implications (from explainig dark matter to changing fabric of space... I'm not saying that's what would happen, but it could).

[Chris Peterson]

obviosly mark is not so good with 'right' examples of physical limitations that were overcomed. better examples would be indivisibility of matter, then indivisibility of atoms, then indivisibility of particles, currently indivisibility of quarks... just because we are out of resources to go any deeper that way, doesn't mean there's nowhere to go in principle. and if we could go there, who knows what kind of physical forces we might find, and what would be macroscopic implications (from explainig dark matter to changing fabric of space... I'm not saying that's what would happen, but it could).

I'd argue that those were not physical limitations at all. They were only technological limitations. And those limitations were overcome precisely because improvements in knowledge made it clear that overcoming them was possible. There are other things that are not attempted because the theory that tells us they are impossible is too well supported to ignore.

[swainy (tc)]

It has everything to do with never giving up. To reach our goals. And understanding, nothing is imposable. We can work out how, and we will.

There are things that are truly limited by physics. Such as how fast you can go. There are things that are impossible. You can spend forever trying to get around natural laws, and it still won't happen. One of the truly important things that comes with a deep understanding of something is the knowledge of what is possible, and therefore worth trying for (despite what might be great practical difficulties), and what is not possible, and therefore should not have time wasted on it.

Hey Chris, I wonder how many times that has been "said" over the last 10 thousand years. Chris, I never wanted to say this. But I have seen something with my own eyes. And I cant explain it. But I saw It, And so did A friend of mine. It was 100 foot from my face, Its was unbelievable, and I will never forget it. I understand what you understand Chris, But I can not understand what, I saw 30 years ago. And I will never believe anything, Until, Its written in stone.

That,s Me Sorry

Guest wrote:obviosly mark is not so good with 'right' examples of physical limitations that were overcomed.

You don't no me very well, Huh?



tc

[Chris Peterson]

Hey Chris, I wonder how many times that has been "said" over the last 10 thousand years.

I don't think that matters. We've only been able to apply scientific thinking towards problems of physics for the last few hundred years. And that way of thinking makes all the difference.

It doesn't matter if we are correct with our theory. The nature of science is that knowledge always grows; we get closer to "truth" as time passes, never further. The current state of theory tells us what is and is not possible, or it may tell us when we don't know if something is possible. But it is theory that evolves. There is no point in looking for a way to "beat" a physical law. If it can be beat, it isn't a physical law at all. And if that turns out to be the case, it will be understood at some later time. Understood because people applied the scientific method of theorizing and testing, not because anybody tried to "beat" some physical law.

[Guest]

well, the theory behind "cant go faster than light" assumes gradual acceleration of stuff like we did for ages; obviously, whoever is going to work around this limitation has to come up with something radically different, and then theory might just bend enough in his favor.

within current theory, we could perfectly reach stars in reasonably short times at high subluminal speed, as measured by would-be travellers. the problem is that it's going to be one-way ticket, and that's where we could use some time traveling. until there's no time traveling, reaching significant fractions of c is useless, and will not be attempted for _that_ reason.

[swainy (tc)]

It doesn't matter if we are correct with our theory. The nature of science is that knowledge always grows; we get closer to "truth" as time passes, never further. The current state of theory tells us what is and is not possible, or it may tell us when we don't know if something is possible. But it is theory that evolves. There is no point in looking for a way to "beat" a physical law. If it can be beat, it isn't a physical law at all. And if that turns out to be the case, it will be understood at some later time. Understood because people applied the scientific method of theorizing and testing, not because anybody tried to "beat" some physical law.

Tell us?. Work it out for your self. Next you will be telling me, France, the other side of the English Channel, is the end of the world.

tc

[Chris Peterson]

Tell us?. Work it out for your self. Next you will be telling me, France, the other side of the English Channel, is the end of the world.

You're totally missing the point of what I'm saying. Several points, in fact.

[geckzilla]

Dear Diary,
I'm thoroughly convinced Swainy is affected by some form of delusion. It's impossible to argue with him simply with logic. A breakdown of the delusion is required. Further examination is required.

[Henning Makholm]

well, the theory behind "cant go faster than light" assumes gradual acceleration of stuff like we did for ages;

No it doesn't. Popular accounts of relativity needs to answer the question of why one couldn't break the lightspeed barrier simply by gradually accelerating past it, but these answers are not the theory's reason why faster-than-light communication is impossible in principle.

The reason for the light-speed maximum has nothing to do with gradual acceleration. It is because communication faster than light is always, for some observer moving sufficiently fast in the right direction, communication that arrives before it is sent. A conspiracy of observers with large mutual velocities which were in possesion of faster-than-light signaling could work together to achieve real backwards-in-time communication, where a message is received by some observer before he himself sends it later.

This is therefore considered to be impossible, because it would entail time travel and the destruction of causality.

[neufer]

well, the theory behind "cant go faster than light" assumes gradual acceleration of stuff like we did for ages;

No it doesn't. Popular accounts of relativity needs to answer the question of why one couldn't break the lightspeed barrier simply by gradually accelerating past it, but these answers are not the theory's reason why faster-than-light communication is impossible in principle.

The reason for the light-speed maximum has nothing to do with gradual acceleration. It is because communication faster than light is always, for some observer moving sufficiently fast in the right direction, communication that arrives before it is sent. A conspiracy of observers with large mutual velocities which were in possesion of faster-than-light signaling could work together to achieve real backwards-in-time communication, where a message is received by some observer before he himself sends it later.

This is therefore considered to be impossible, because it would entail time travel and the destruction of causality.

Techy, a. [From OE. tecche, tache, a habit, bad habit, vice, OF. tache, teche, a spot, stain, blemish, habit, vice, F. tache a spot, blemish; probably akin to E. tack a small nail.] Peevish; fretful; irritable.

Tacky, a. [Cf. Techy, Tack a spot.] (Webster 1913)

• 1) Sticky; adhesive; raw; -- said of paint, varnish, etc., when not well dried.
  2) In poor taste; appearing cheap; gaudy; unstylish.
  3) Tactless; in poor taste; -- used to describe behavior.

<<A Tachyon (Greek: ταχύς, "swift" + English: -on "elementary particle") is a hypothetical subatomic particle that moves faster than light. In the language of special relativity, a tachyon is a particle with space-like four-momentum and imaginary proper time. A tachyon is constrained to the space-like portion of the energy-momentum graph. Therefore, it cannot slow down to subluminal speeds. The first description of tachyons is attributed to German physicist Arnold Sommerfeld. However, it was George Sudarshan, Olexa-Myron Bilaniuk, Vijay Deshpande, and Gerald Feinberg (who originally coined the term in the 1960s) who advanced a theoretical framework for their study.

If tachyons were conventional, localizable particles that could be used to send signals faster than light, this would lead to violations of causality in special relativity. But in the framework of quantum field theory, tachyons are understood as signifying an instability of the system and treated using tachyon condensation, rather than as real faster-than-light particles, and such instabilities are described by tachyonic fields. Tachyonic fields have appeared theoretically in a variety of contexts, such as the bosonic string theory.
..................................................
Cherenkov radiation

Taking the formalisms of electromagnetic radiation and supposing a tachyon had an electric charge—as there is no reason to suppose a priori that tachyons must be either neutral or charged—then a charged tachyon must lose energy as Cherenkov radiation—just as ordinary charged particles do when they exceed the local speed of light in a medium. A charged tachyon traveling in a vacuum therefore undergoes a constant proper time acceleration and, by necessity, its worldline forms a hyperbola in space-time. However, as we have seen, reducing a tachyon's energy increases its speed, so that the single hyperbola formed is of two oppositely charged tachyons with opposite momenta (same magnitude, opposite sign) which annihilate each other when they simultaneously reach infinite speed at the same place in space. (At infinite speed the two tachyons have no energy each and finite momentum of opposite direction, so no conservation laws are violated in their mutual annihilation.) Even an electrically neutral tachyon would be expected to lose energy via gravitational Cherenkov radiation, because it has a gravitational mass, and therefore increase in speed as it travels, as described above.
..................................................
Quantum field theory

Quantizing tachyons shows that they must be spinless particles which obey Fermi-Dirac statistics; i.e., tachyons are Scalar fermions, a combination which is not permitted for ordinary particles. They also must be created and annihilated in pairs.
..................................................
Causality

The property of causality is a fundamental principle of theoretical particle physics. If tachyons could be used to transmit information faster than light, then according to relativity they could also be used to violate causality using a scheme sometimes known as the "tachyon telephone paradox". This can be understood in terms of the relativity of simultaneity in special relativity, which says that in some cases different inertial reference frames will disagree on whether two events at different locations happened "at the same time" or not, and they can also disagree on the order of the two events (technically, these disagreements occur when spacetime interval between the events is 'space-like', meaning that neither event lies in the future light cone of the other).

It has been argued that we can avoid the notion of tachyons traveling into the past using the Feinberg reinterpretation principle which states that a negative-energy tachyon sent back in time in an attempt to violate causality can always be reinterpreted as a positive-energy tachyon traveling forward in time. This is because observers cannot distinguish between the emission and absorption of tachyons. For a tachyon, there is no distinction between the processes of emission and absorption, because there always exists a sub-light speed reference frame shift that alters the temporal direction of the tachyon's world-line. The attempt to detect a tachyon from the future (and violate causality) can actually create the same tachyon and sends it forward in time (which is causal).

In fact, there are arguments from quantum field theory suggesting that even if tachyons existed, they could not be used to transmit information faster than light at all, either because disturbances in the quantum field for a tachyon would not actually propagate faster than light, or because the tachyon is impossible to localize. Without the possibility of faster-than-light information transmission, the problem of backwards-in-time information transmission could be avoided as well.
................................
Despite the theoretical arguments against the existence of tachyon particles, experimental searches have been conducted to test the assumption against their existence; however, no experimental evidence for the existence of tachyon particles has been found.>>

[Guest]

It is because communication faster than light is always, for some observer moving sufficiently fast in the right direction, communication that arrives before it is sent. A conspiracy of observers with large mutual velocities which were in possesion of faster-than-light signaling could work together to achieve real backwards-in-time communication, where a message is received by some observer before he himself sends it later.

So?

This is therefore considered to be impossible, because it would entail time travel and the destruction of causality.

In other words, it is impossible because you cant wrap your head around its consequences. Doesn't sound like true physical limitation to me.

[Chris Peterson]

This is therefore considered to be impossible, because it would entail time travel and the destruction of causality.

In other words, it is impossible because you cant wrap your head around its consequences. Doesn't sound like true physical limitation to me.

That's not what he is saying at all.

[Guest]

Then what _does_ he say? Why dont you (two) elaborate? Is there anything absolutely impossible about causality violations or time travelling? Is there a theorem saying that the universe will go big bang if any of the above would actually happen? Im sure if that's physically possible, the universe has nice way to handle all the paradoxes you can come up with, they are paradoxes merely because we don't know anything about that way. Don't get me wrong, it could still be impossible after all, I'm just saying that you can't know for sure when our experience doesn't come even close to such situations.

[Chris Peterson]

Then what _does_ he say? Why dont you (two) elaborate?

What he is saying (as am I) is that there is a very powerful theory that concludes it is impossible. And that theory is extremely well supported by many independent lines of evidence. Is it possible that the theory is wrong, or so incomplete as to be wrong about this? Of course. But it is so extremely unlikely that we can, with a very, very high level of confidence, state that transferring information faster than c is impossible, and say the same for the related case of transferring information backwards in time.

While proper scientific skepticism requires us to technically exclude impossible in favor of extreme unlikelihood, scientific rationalism tells us that it is not profitable to waste much effort looking for alternatives to very well supported theories.

[orin stepanek]

Maybe I'm all wet; but the way I see it it that an event happens at a certain point of time and space. To go back in time you would have to move the whole universe to that point in space. Since the universe is forever moving that spot in time and space is forever gone. We are time travelers going into the future; one day at a time. To go back in time we have history; news reels; radio; TV; books; movies; memories; etc. If somehow a Time Machine were developed; I'm afraid man would go back in time and change history. I for one; hopes that never happens.

[Chris Peterson]

If somehow a Time Machine were developed; I'm afraid man would go back in time and change history. I for one; hopes that never happens. :?

There's an interesting argument against time travel that says the Universe evolved into a state where time travel is impossible. This occurred because in every version where time travel was possible, it resulted in the past being changed. Eventually the change was one where time travel was impossible (or at least, never occurs/occurred), and that Universe was the final, stable one.

It's an explanation that is likely to appeal to those familiar with control theory.

[swainy (tc)]

Gravity stops light, Light can not escape a Black Hole. They Say A Black Hole also Stops Time. Time started At T=0 Just like inflation, and expansion, Everything including time was Created. You cant just say part of the universe was created, and then was left to create itself. All of Time was created. The last 13.7 billion years was created, and the next 20 billion years was created. we just cant see it. The fact that Time never started ticking, for some of the real big black holes, should point you to some sort of answer. Now, If all of Time was created at the same time, Then all of time should be accessible. Now when scientist say that being in the vicinity of a Black Hole, Or traveling at the speed of light, We see Time changing. This shows me that Time is some how malleable, In certain aspects and ways. It tells me I can speed time up or slow it down, if i get the energy or tech to do this. There is nothing wrong, In believing, that any part of the giant jigsaw we have, can be worked out.
There is a reason for every part of it.

tc

[Guest]

...and that Universe was the final, stable one.

says who? let's say the past is actually changed every minute. how would you even notice it?

[bystander]

Why dont you (two) elaborate?

Why don't you just log in and post under your id?

I'm fairly certain I know who you are, what I don't understand is why you are hiding.

[Guest]

Now, If all of Time was created at the same time, Then all of time should be accessible.

Right... what?

Now when scientist say that being in the vicinity of a Black Hole, Or traveling at the speed of light, We see Time changing. This shows me that Time is some how malleable, In certain aspects and ways. It tells me I can speed time up or slow it down, if i get the energy or tech to do this. There is nothing wrong, In believing, that any part of the giant jigsaw we have, can be worked out.

I like it how you use same theory Chris is using to argue against you. However, your argument is weak, all you are saying is that you hope for new theory with broader range of time "changes" available; in present theory you don't have much room for that.

[Chris Peterson]

...and that Universe was the final, stable one.

says who? let's say the past is actually changed every minute. how would you even notice it?

I was only describing a though provoking idea about how the Universe (or a universe) might evolve into a stable state that disallows time travel. I wasn't proposing it as a serious scientific theory, or taking much of a position about it one way or the other.

[Guest]

Why dont you (two) elaborate?

Why don't you just log in and post under your id?

I'm fairly certain I know who you are, what I don't understand is why you are hiding.

not hiding, how can you hide when there's "see who posted from this ip" feature this is my wife's notebook, so I just open up the site from history and type right away, too lazy to go and log in.

[Chris Peterson]

Gravity stops light, Light can not escape a Black Hole.

Light being unable to escape a black hole most assuredly is not equivalent to "gravity stops light".

They Say A Black Hole also Stops Time.

I don't know which "they" you are referring to, but this is not mainstream theory. You are vastly oversimplifying the situation.

Now, If all of Time was created at the same time, Then all of time should be accessible.

Why? That does not follow from any logic I can see. All of space was created at the same time, but it is most certainly not all accessible.

Now when scientist say that being in the vicinity of a Black Hole, Or traveling at the speed of light, We see Time changing. This shows me that Time is some how malleable, In certain aspects and ways. It tells me I can speed time up or slow it down, if i get the energy or tech to do this.

Again, you fail to understand relativity. It does not say that time changes, or is malleable, or anything of the sort. It only says that observers in one non-inertial frame of reference observe time in a different frame of reference as moving at a different rate. It does not say that time actually changes its rate of flow. By analogy, consider the simple case of motion in inertial frames. If you observe the velocity of something outside your frame, and then change your own velocity and observe it again, it will appear to have changed velocity. But I don't think anybody would rationally say that you changed that object's velocity, or that velocity was somehow "malleable" as applied to what you were observing. You are simply seeing a relative effect- one that will look completely different to observers in other frames.