111 réponses à ce sujet

[RedKnight410]

it's not relative either, doesn't change no matter the frame you are in. I'm not going to right out the formula that explains how to add velocities when moving at relativistic speeds but look it up if you need clarification. I'm not saying she would see herself as frozen in place; it's just a principle of physics that if you were to say be falling then you would perceive the ground to be moving towards you not the other way around. Common sense tells us that is not the case but it's how you go about doing relativity problems. Finally, I never questioned your grasp of time dilation.

[Evil Johnny 666]

Just for fun, some day I did some calculations regarding ME's FTL speed (it's calculable based on the codex info) and with different accelerations. I don't have the results anymore, but with an acceleration of 3 gs (space shuttle), they would reach the 12 ly (if I can remember correctly, FTL should enable you to travel 12 ly in a day) LOOONG before attaining FTL. I did some others with different accelerations, and even accelerations that can be only be suffered for a second or two before someone dies from it would need a ridiculous amount of time to reach that speed. I think some of my calculations returned results of a minimum of 100 years, sometimes it'd take 300 years. And then, someone's resistance (lethality) to acceleration is dependant of the time you're under that acceleration. So you might die of a 3 g acceleration if you're subject to it for more than a year or something - or less. Of course it's all science fiction, but it's fun to see such stuff.

[TheJiveDJ]

RedKnight410 wrote...

it's not relative either, doesn't change no matter the frame you are in. I'm not going to right out the formula that explains how to add velocities when moving at relativistic speeds but look it up if you need clarification. I'm not saying she would see herself as frozen in place; it's just a principle of physics that if you were to say be falling then you would perceive the ground to be moving towards you not the other way around. Common sense tells us that is not the case but it's how you go about doing relativity problems. Finally, I never questioned your grasp of time dilation.

Okay okay to me it seems like a case of tomato/tomoto.  You say the gound is moving toward me, I say I'm moving toward ground.  Two sides of the same coin really.  We're getting into the semantics of it all when you and me are arguing the same point just from different perspectives.

[TheJiveDJ]

Evil Johnny 666 wrote...

Just for fun, some day I did some calculations regarding ME's FTL speed (it's calculable based on the codex info) and with different accelerations. I don't have the results anymore, but with an acceleration of 3 gs (space shuttle), they would reach the 12 ly (if I can remember correctly, FTL should enable you to travel 12 ly in a day) LOOONG before attaining FTL. I did some others with different accelerations, and even accelerations that can be only be suffered for a second or two before someone dies from it would need a ridiculous amount of time to reach that speed. I think some of my calculations returned results of a minimum of 100 years, sometimes it'd take 300 years. And then, someone's resistance (lethality) to acceleration is dependant of the time you're under that acceleration. So you might die of a 3 g acceleration if you're subject to it for more than a year or something - or less. Of course it's all science fiction, but it's fun to see such stuff.

Interesting.  I'd argue that it's not the duration of gforces but the speed at which you accelerate.  A 3g acceleration could be lethal if you accelerate to 3gs in under 5 seconds lets say whereas if you accelerated to 3gs over 10 minutes it wouldn't be anywhere near as bad.  Once your body has the inertia it should be able to withstand acceleration forces of well over 25gs and we know this because that is the speed at which astronaughts re-enter Earths atmosphere.

[adam_grif]

ok so one of the things Mr. Albert Einstein talked about in his Teory of
relativity was that if you were albe to travel with a speed close to
the speed of light, or even faster, you would actually travel through
time, since the time you experience is different from the time for those
observing "you", thus traveling through time.

You're close. It does involve time travel, but not in the conventional sense, you don't just go faster and start moving in reverse, however you do end up in situations where you warp out to Alpha Centauri and back, and you arrive before you left. It's time travel but you always seem to be moving forwards from your own perspective. The light speed limit is the only thing enforcing causality given relative time (which has been experimentally verified). To save time I'll just copy+paste a post I made on the topic a long time ago:

adam_grif wrote...

Relativistic Time Dilation means that as you approach C, everybody
around you seems to be moving slower than you. To them, you appear to be
moving slower. This is NOT just an optical illusion of some sort, it's
actually happening.



The following is known as the Tachyon pistol duel thought experiment. It
demonstrates why FTL travel results in time paradoxes. For simplicity
of calculation's sake, FTL is considered to have infinite speed,
striking its target instantly. The same effects apply with limited FTL
velocities, but they are a **** to do the number crunching with.



Man A and Man B meet at a point in space, and agree to turn around, move
away from each other, count down 8 seconds, then turn and fire their
weapons at each other. We will follow from man A's perspective.



Both parties exit and travel away from each other at 0.866 C. Man A
counts down to 0, turns and then fires. Due to time dilation, when Man A
counts to zero, Man B has only counted down to 4, thus his shot flies
past Man B at 4 seconds.



Enraged that Man A has fired before he has hit 0, he fires at 4 seconds,
and due to time dilation, man A has only counted down to 6! It strikes
man A and kills him dead after he has counted down only 2 seconds, a
full 6 seconds before he fired his initial shot. A classic grandfather
paradox. It gets made worse by the fact that if you started from man B's
perspective instead of man A, the exact inverse happens, with man B
dead 6 seconds before he fires his shot instead.



So we're not only left with a grandfather paradox, but 2 events that both should have happened, but are mutually exclusive.

Now on to some of the replies that made me RAGE.

Mister Mida wrote...

And concerning Einstein's theory: It's still a theory. So far no one we know off has been able to actually test it.

Time dilation has been experimentally verified, and the GPS satellites in earth orbit have to by synchronized with Earth clocks every 24 hours or so because they experience gravitational time dilation. One day they only get out of synch very slightly, but if you leave it for months it builds up to significant levels.

Mass-energy equivelance has also been experimentally verified (atomic weapons and antimatter anihilation tests), as has the light-speed limit (high energy particle accelerators).

Phaedon wrote...

Einstein's theory is rather outdated, also, check the Alcubierre drive and wormholes.

Outdated in the sense that they are still highly relevant, have been experimentally verified as true to a very high degree of accuracy, and are inadequate only when dealing with quantum-scale phenomena, whose governing theory (quantum theory) is useless at describing macro-scale events.

Relativity is not wrong, it's incomplete. Newton was also incomplete, but his principles still hold true today in all but the most extreme circumstances (where we need relativity to take over).

Alcubierre drives and Wormholes both require black magic to work (they're "possible" only in the most physically asinine sense of the word, given that they demand exotic matter, naked singularities and preposterous energies to get the former to work, and there are no known methods by which wormholes can form at all even though their geometry is not impossible), and neither explains how FTL will not result in time travel. Both of those designs still create paradoxes, assuming they were ever to be constructed.

Finding a way to "break the light barrier" is called "The Easy Problem of FTL". Finding a way to explain why paradoxes don't occur when you do break it is called "The Hard Problem of FTL".

xentar wrote...

(it would help it reach the speed of light easier, though).

Not really, because you need infinite energy to reach C. It takes the same infinite energy to make 1 gram reach C as it does for 10000000000 tonnes to reach it.

[Spornicus]

It's probably wrong, but eh, it's a science fiction game. There's gotta be some way to travel immense distances in little time.

[adam_grif]

I disagree. You can craft beautiful stories even with the FTL limit in place. Science Fiction doesn't have to be pew pew space ship battles and galactic politics. A lot of the best SciFi isn't even close to that.



Even if you do want space opera, you can do something like Revelation Space, which enforces it's FTL limit pretty tightly (although second book onwards gets ridiculous with magitech even though there is no FTL).

[TheJiveDJ]

adam_grif wrote...

ok so one of the things Mr. Albert Einstein talked about in his Teory of
relativity was that if you were albe to travel with a speed close to
the speed of light, or even faster, you would actually travel through
time, since the time you experience is different from the time for those
observing "you", thus traveling through time.

You're close. It does involve time travel, but not in the conventional sense, you don't just go faster and start moving in reverse, however you do end up in situations where you warp out to Alpha Centauri and back, and you arrive before you left. It's time travel but you always seem to be moving forwards from your own perspective. The light speed limit is the only thing enforcing causality given relative time (which has been experimentally verified). To save time I'll just copy+paste a post I made on the topic a long time ago:

adam_grif wrote...

Relativistic Time Dilation means that as you approach C, everybody
around you seems to be moving slower than you. To them, you appear to be
moving slower. This is NOT just an optical illusion of some sort, it's
actually happening.



The following is known as the Tachyon pistol duel thought experiment. It
demonstrates why FTL travel results in time paradoxes. For simplicity
of calculation's sake, FTL is considered to have infinite speed,
striking its target instantly. The same effects apply with limited FTL
velocities, but they are a **** to do the number crunching with.



Man A and Man B meet at a point in space, and agree to turn around, move
away from each other, count down 8 seconds, then turn and fire their
weapons at each other. We will follow from man A's perspective.



Both parties exit and travel away from each other at 0.866 C. Man A
counts down to 0, turns and then fires. Due to time dilation, when Man A
counts to zero, Man B has only counted down to 4, thus his shot flies
past Man B at 4 seconds.



Enraged that Man A has fired before he has hit 0, he fires at 4 seconds,
and due to time dilation, man A has only counted down to 6! It strikes
man A and kills him dead after he has counted down only 2 seconds, a
full 6 seconds before he fired his initial shot. A classic grandfather
paradox. It gets made worse by the fact that if you started from man B's
perspective instead of man A, the exact inverse happens, with man B
dead 6 seconds before he fires his shot instead.



So we're not only left with a grandfather paradox, but 2 events that both should have happened, but are mutually exclusive.

Now on to some of the replies that made me RAGE.

Mister Mida wrote...

And concerning Einstein's theory: It's still a theory. So far no one we know off has been able to actually test it.

Time dilation has been experimentally verified, and the GPS satellites in earth orbit have to by synchronized with Earth clocks every 24 hours or so because they experience gravitational time dilation. One day they only get out of synch very slightly, but if you leave it for months it builds up to significant levels.

Mass-energy equivelance has also been experimentally verified (atomic weapons and antimatter anihilation tests), as has the light-speed limit (high energy particle accelerators).

Phaedon wrote...

Einstein's theory is rather outdated, also, check the Alcubierre drive and wormholes.

Outdated in the sense that they are still highly relevant, have been experimentally verified as true to a very high degree of accuracy, and are inadequate only when dealing with quantum-scale phenomena, whose governing theory (quantum theory) is useless at describing macro-scale events.

Relativity is not wrong, it's incomplete. Newton was also incomplete, but his principles still hold true today in all but the most extreme circumstances (where we need relativity to take over).

Alcubierre drives and Wormholes both require black magic to work (they're "possible" only in the most physically asinine sense of the word, given that they demand exotic matter, naked singularities and preposterous energies to get the former to work, and there are no known methods by which wormholes can form at all even though their geometry is not impossible), and neither explains how FTL will not result in time travel. Both of those designs still create paradoxes, assuming they were ever to be constructed.

Finding a way to "break the light barrier" is called "The Easy Problem of FTL". Finding a way to explain why paradoxes don't occur when you do break it is called "The Hard Problem of FTL".

xentar wrote...

(it would help it reach the speed of light easier, though).

Not really, because you need infinite energy to reach C. It takes the same infinite energy to make 1 gram reach C as it does for 10000000000 tonnes to reach it.

Actually if you were traveling at the speed of light everyone else would be moving abnormally fast from your perspective.  Just thought I'd clarify, perhaps you overlooked that.  Explained further, time dilation only works in one direction, forward.  So if I was traveling at the speed of light and everyone else appeared slower...then technically I am ageing faster than them.  You see where I'm going?  As you approach light speed you are, in effect, traveling into the future.  Logically this means everyone else ages faster than you.  What you'd see if you looked out your space-craft is everyone else moving very very fast.  What they'd see if they peered into your spacecraft would be you...frozen in time.

Modifié par TheJiveDJ, 17 janvier 2011 - 01:20 .

[adam_grif]

Actually if you were traveling at the speed of light everyone else would be moving abnormally fast from your perspective. Just thought I'd clarify, perhaps you overlooked that. Explained further, time dilation only works in one direction, forward. So if I was traveling at the speed of light and everyone else appeared slower...then technically I am ageing faster than them. You see where I'm going? As you approach light speed you are, in effect, traveling into the future. Logically this means everyone else ages faster than you. What you'd see if you looked out your space-craft is everyone else moving very very fast. What they'd see if they peered into your spacecraft would be you...frozen in time.

This website is usually considered the best SciFi resource on the whole internet, read what it has to say on the matter.



I would also direct you to this post from Ars Technica:

According to special relativity, the global concept of 'simultaneity' is essentially destroyed. Two events which happen simultaneously in one frame will happen at different times in another.



The classic example used to demonstrate this is the railroad car with a flash bulb in the middle and photon detectors at each end. To an observer standing on the rail car, the two photon detectors will go off simultaneously after a flash. However, to an observer on the ground, the rear detector will go off first, because it is moving to meet the photons emitted by the flash bulb. Additionally, an observer moving on a parallel line going faster will observe the front detector going off first, since in his reference frame the rail car is moving backwards.



What does this have to do with causality? Well, a central tenet of causality is that event A must precede event B in order for event A to cause event B. Since the precise timing of events can shift (as demonstrated above) in relativistic frames, special relativity extends this statement. Event A must precede Event B in all reference frames.



It is at this point that one really must look at the math, but what one finds if one does is that that this last statement breaks down fairly simply. If two events are separated by enough space that light cannot get from one event to the other event, then there is some relativistic frame in which the order of the events changes. If, however, the two events are separated by enough time that light can get from one event to the other event, then one event will precede the other in all reference frames. The first scenario is called a 'spacelike' separation, while the second is called a 'timelike' separation.



How does this relate to time travel? Well, consider two events, A and B separated by a spacelike interval. If Event A can send a message to Event B faster than light, then that message can travel backwards in time, since in some reference frame Event B happens before Event A.

Finally, there is this diagram that may or may not make a lot of sense depending on your level of familiarity with relativity:

[Spartas Husky]

damn this has gone way beyond my paygrade lol. ...this is one of those that call for this quote "agree to disagree"

[s_mirage]

Stensig wrote...

Spartas Husky wrote...

photons dont have mass dude.

I love this. Decades from now.... or prolly a century or so into the future our progeny will be laughing at us lol

Idd they will. But seriously check it... it does have a mass, but the fact that its messured in electromagnetic volt says how small it is, and even in that messuring, its an insaly small number..

No they don't. The common definition for mass, and what people here are referring to, is rest mass. Photons have no rest mass. What you are referring to is relativistic mass, which in this case is simply the kinetic energy level of a photon.

[xentar]

s_mirage wrote...

No they don't. The common definition for mass, and what people here are referring to, is rest mass. Photons have no rest mass. What you are referring to is relativistic mass, which in this case is simply the kinetic energy level of a photon.

And I was just about to make a rage post...