Where da Physics junkies at?

[Evil_Sabre]

Ok so I've been trying to explain to a friend why time slows down prospectively as one approaches the speed of light, or increases their speed at all for that matter. I know this has been proven but I'm not sure if the way I'm explaining it is correct. As far as I understand the energy in spacetime cannot change; so if one increases distance (due to speed increase) your time will have to decrease to make up for it. So the faster you travel, the slower time seems to be. I've read the twin paradox and such but it's still a bit over my head.

 

Any help is appreciated

[Hegel]

Your explanations seem rather strange to me. From what I know time dilation follows directly from the principle of equivalence, and if you conduct the 'thought experiment' you should be able to derive the Lorentz transformation without much difficulty. I am not sure which textbook you use but the Feynman Lectures on Physics has a rather neat explanation of relativity.

[i_love_burritos]

Yarr, matey. You would be correct.

 

Okay, I'll try explaining it simply for you measly wenches. Okay with me matey Newton for the last 250 years we've had something like : F= d(mv)/dt and we've always thought m [mass] is constant. But me matey Einstein, yarr bless im', correctly stated the mass of a body, increases with velocity.

 

Hence, correctly, it is now, m = m0/(1-v^2/c^2)^(1/2). As you probably notice, in normal instances mass increase is tiny [due to the limit of c^2, which be very very large indeed. For a practical example, let’s have Blackbeard and Calio Jack. Now me matey Blackbeard is moving in a given direction and for posterity’ sake let that direction be B for Blackbeard.

 

Now, Blackbeard is moving at the velocity u in direction B. On this plane, Blackbeard’s location at any given time due to his constant velocity is B prime or the derivative of B. Now me matey Calio Jack, seeing Blackbeard, keep in mind Calio Jack is standing still, sees Blackbeard on the plane and measures Blackbeards’ starting and moving position as his B distance, and has the point B prime within the plane. Avast !, consider this matey, v = deltaX/deltaT, and since Blackbeard has begun sailing [did I mention they were on boats ?] Blackbeard has moved his velocity and Calio Jack’s time [t].

 

Hence his point on the plane [seven seas] is given by B prime = B – ut. So for any given point on a plane, B prime is B, C prime is C and D prime is D and so on…Yarr be following matey ? Now this system is closed and hence Newtons laws apply do not apply all the same in a moving aswell as stationary system. Moving on to Lorentz matey. The Lorentz transformation when these interesting facts o’ matter are substituted into Maxwell. B prime = B – ut/(1-u^2/c^2)^1/2 and so on, but when to time as shown above obtained, time prime = (t – (uB/c^2))/ (1-u^2/c^2)^(1/2), notice that they same the same no mater what primes are scallwagged in !

 

Yarr, we be sailing off to Lorentz’ Treasure Island now ! Yarr, now that we have the position of a point, let’s have Blackbeards’ sea and Calio Jack’s sea. Now Calio Jack sees how far Blackbeard has sailed in Blackbeards’ sea [remember we pirates be sailing on the seas]. So Calio Jack says Blackbeard has sailed B prime units of length, in direction B.

 

However Calio Jack is using measurements relative to the Calio Jack sea, not the Blackbeard sea, he be using a normal mile instead of a nautical mile. [Or something like that, remember that Calio Jack’s nautical mile is shorter than Blackbeards’ nautical mile] and so according to Jack, Blackbeard has sailed Bprime*(1-u^2/c^2)^(1/2) nautical miles, in the Blackbeard sea.

 

So if the Blackbeard sea has travelled a distance of UT in the Jack sea, Mr. Calio Jack would say that Blackbeard has sailed B = B prime*(1-u^2/c^2)^(1/2)+UT. Yarr har har matey, we be sailing around in circles ! But land ahoy ! We be upon Lorentz Island and feast your eyes matey, the booty ! B prime = B – UT/(1-u^2/c^2)^(1/2). Shiver me timbers !!! Rum and wenches all for one and one for all !

 

Reading in a pirate voice is optional.

[Stommel]

Basically special relativity relies on one fact: The laws of physics apply equally in EVERY inertial referance frame (ones moving at constant velocity relative to each other).

 

Check out the Michelson-Morley experiment, the first experiment that tested special relativity directly (though they managed to make up some other/ether excuse......that was bad, sorry).

It's basically just a thought experiment with some triangle manipulation and using the fact that light moves at c in all reference frames, due to the first statement.

 

 

p.s. I'm liking the pirates meet spec. rel. version Adrenal

[i_love_burritos]

p.s. I'm liking the pirates meet spec. rel. version Adrenal

 

Yarr, hearty thanks to ye'. I woe it be making sense, yet be you a landlubber ?

[Will H]

Yarr, matey. You would be correct.

 

Okay, I'll try explaining it simply for you measly wenches. Okay with me matey Newton for the last 250 years we've had something like : F= d(mv)/dt and we've always thought m [mass] is constant. But me matey Einstein, yarr bless im', correctly stated the mass of a body, increases with velocity.

 

Hence, correctly, it is now, m = m0/(1-v^2/c^2)^(1/2). As you probably notice, in normal instances mass increase is tiny [due to the limit of c^2, which be very very large indeed. For a practical example, lets have Blackbeard and Calio Jack. Now me matey Blackbeard is moving in a given direction and for posterity sake let that direction be B for Blackbeard.

 

Now, Blackbeard is moving at the velocity u in direction B. On this plane, Blackbeards location at any given time due to his constant velocity is B prime or the derivative of B. Now me matey Calio Jack, seeing Blackbeard, keep in mind Calio Jack is standing still, sees Blackbeard on the plane and measures Blackbeards starting and moving position as his B distance, and has the point B prime within the plane. Avast !, consider this matey, v = deltaX/deltaT, and since Blackbeard has begun sailing [did I mention they were on boats ?] Blackbeard has moved his velocity and Calio Jacks time [t].

 

Hence his point on the plane [seven seas] is given by B prime = B ut. So for any given point on a plane, B prime is B, C prime is C and D prime is D and so onYarr be following matey ? Now this system is closed and hence Newtons laws apply do not apply all the same in a moving aswell as stationary system. Moving on to Lorentz matey. The Lorentz transformation when these interesting facts o matter are substituted into Maxwell. B prime = B ut/(1-u^2/c^2)^1/2 and so on, but when to time as shown above obtained, time prime = (t (uB/c^2))/ (1-u^2/c^2)^(1/2), notice that they same the same no mater what primes are scallwagged in !

 

Yarr, we be sailing off to Lorentz Treasure Island now ! Yarr, now that we have the position of a point, lets have Blackbeards sea and Calio Jacks sea. Now Calio Jack sees how far Blackbeard has sailed in Blackbeards sea [remember we pirates be sailing on the seas]. So Calio Jack says Blackbeard has sailed B prime units of length, in direction B.

 

However Calio Jack is using measurements relative to the Calio Jack sea, not the Blackbeard sea, he be using a normal mile instead of a nautical mile. [Or something like that, remember that Calio Jacks nautical mile is shorter than Blackbeards nautical mile] and so according to Jack, Blackbeard has sailed Bprime*(1-u^2/c^2)^(1/2) nautical miles, in the Blackbeard sea.

 

So if the Blackbeard sea has travelled a distance of UT in the Jack sea, Mr. Calio Jack would say that Blackbeard has sailed B = B prime*(1-u^2/c^2)^(1/2)+UT. Yarr har har matey, we be sailing around in circles ! But land ahoy ! We be upon Lorentz Island and feast your eyes matey, the booty ! B prime = B UT/(1-u^2/c^2)^(1/2). Shiver me timbers !!! Rum and wenches all for one and one for all !

 

Reading in a pirate voice is optional.

 

I hereby propose that all physics lessons must be in a pirate voice forthwith, and all examples within must be pertaining to pirates. All who say yarr?

[tortilliachp]

I would start by explaining gravitational time dialation, and thus in essence what gravity is as a force. that is a much simpler concept than the concept of accelerated frames of reference.

 

basically, gravity distorts space-time (3d where time is the 4th dimension). the stronger the effect of gravity, the more distorted space-time is and consequently, the slower time runs. It's essentially putting a heavy object on a trampoline and watching the trampoline curve. as the trampoline curves, the closer you are to the heavy object, the larger area of trampoline is squished together in the same "flat" area as the trampoline without the heavy object on it. As seen in this 2d representation (where the results are observed in the 3d curvature), we need an extra dimension to explain the distortion of a previous one. we can't visualize a 4th dimension of space, so a 3d reprsenation is simply a "mind[bleep]"

 

When you then, close to the heavy object on the trampoline, cover a larger area of the flat dimension of the trampoline (which represents the dimensions of space) you are covering a larger space in the same time based on your locality: time is moving more slowly.

 

that's the easy part. everyone can understand a trampoline bending. that's a good proof of concept, which translates into the real world very easily: time goes so much slower in a GPS sattelite that the clocks need to be adjusted daily for the GPS system to remain accurate.

 

Then, to your real question:

 

first of all, many people think that mass and energy are two different things. In space-time they are the same, as postulated by e=mc^2. gravity then becomes a force affiliated with energy. the energy of mass can be divided into internal energy and motion energy: there is the internal energy which are the direct forces between the particles of a mass holding it together as an object; and there is the motion energy of the object which is basically the energy that it is holding when it moves around.

 

So then, the faster an object is moving the more energy it has. more energy means more gravitational force, and more gravitational force means a "heavier" object has been placed on our metaphorical trampoline (e=mc^2): the area covered close to the heavy object becomes greater with more energy, and then time slows down the faster you travel.

[Danqazmlp]

I don't know anything except that I'm sure I heard somewhere (May have been an article recently by Hawking on time machines) that using the LHC it was proven, as a particle which would normally degrade in x time took four times longer to degrade while going around the collider at almost the speed of light.

[tortilliachp]

I don't know anything except that I'm sure I heard somewhere (May have been an article recently by Hawking on time machines) that using the LHC it was proven, as a particle which would normally degrade in x time took four times longer to degrade while going around the collider at almost the speed of light.

 

yeah it's been proven time and time again, that's not the issue at hand: the issue is how ot explain it to someone who doesn't know a lot of physics :mrgreen:

[Evil_Sabre]

I would start by explaining gravitational time dialation, and thus in essence what gravity is as a force. that is a much simpler concept than the concept of accelerated frames of reference.

 

basically, gravity distorts space-time (3d where time is the 4th dimension). the stronger the effect of gravity, the more distorted space-time is and consequently, the slower time runs. It's essentially putting a heavy object on a trampoline and watching the trampoline curve. as the trampoline curves, the closer you are to the heavy object, the larger area of trampoline is squished together in the same "flat" area as the trampoline without the heavy object on it. As seen in this 2d representation (where the results are observed in the 3d curvature), we need an extra dimension to explain the distortion of a previous one. we can't visualize a 4th dimension of space, so a 3d reprsenation is simply a "mind[bleep]"

 

When you then, close to the heavy object on the trampoline, cover a larger area of the flat dimension of the trampoline (which represents the dimensions of space) you are covering a larger space in the same time based on your locality: time is moving more slowly.

 

that's the easy part. everyone can understand a trampoline bending. that's a good proof of concept, which translates into the real world very easily: time goes so much slower in a GPS sattelite that the clocks need to be adjusted daily for the GPS system to remain accurate.

 

Then, to your real question:

 

first of all, many people think that mass and energy are two different things. In space-time they are the same, as postulated by e=mc^2. gravity then becomes a force affiliated with energy. the energy of mass can be divided into internal energy and motion energy: there is the internal energy which are the direct forces between the particles of a mass holding it together as an object; and there is the motion energy of the object which is basically the energy that it is holding when it moves around.

 

So then, the faster an object is moving the more energy it has. more energy means more gravitational force, and more gravitational force means a "heavier" object has been placed on our metaphorical trampoline (e=mc^2): the area covered close to the heavy object becomes greater with more energy, and then time slows down the faster you travel.

 

I like the pirate explanation but I only fully understood portions of it. This is a little more concise, thanks for all the replies.

[anonymous_user]

Hmm, just a thought. If time goes slower as you speed up, let's say you go so fast that it takes no time at all. Would you go back in time if you moved any faster than that, since it would take negative time? I know it will never be possible to go that fast, just wondering if physics works that way. I can't grasp all the hardcore physics though.

[Danqazmlp]

Nope, as far as speed is concerned, you cannot go faster than the speed of light.

[stevepole]

the issue is how ot explain it to someone who doesn't know a lot of physics :mrgreen:

 

Solution: make him watch one of these Into the Universe with Stephen Hawking on the Discovery Channel. I remember them explaining it during one of the shows. Why he'll belief: A) It's on TV B) It's the Discovery Channel C) It's Stephen Hawking

[Evil_Sabre]

the issue is how ot explain it to someone who doesn't know a lot of physics :mrgreen:

 

Solution: make him watch one of these Into the Universe with Stephen Hawking on the Discovery Channel. I remember them explaining it during one of the shows. Why he'll belief: A) It's on TV B) It's the Discovery Channel C) It's Stephen Hawking

 

Haha that show is exactly why I posted this. I caught the last few minutes of it and they were talking of this, I didn't catch it early enough to get an in depth explanation, however. Really awesome series by the way.

[tortilliachp]

Nope, as far as speed is concerned, you cannot go faster than the speed of light.

 

well, that's really a simplification of the truth. things cannot cross the boundy of the speed of light. either they've always existed above the speed of light, or below since the bing bang, just like any other mathematical limit you can approach it from either direction. As sub-lightspeed particles we'll never be able to observe above-lightspeed particles and vice versa either.

[Evil_Sabre]

Don't some physicists believe that the initial expansion of the universe exceeded the speed of light because there were no physical laws before there was a "physical" universe?

[The Dark Lord]

Nope, as far as speed is concerned, you cannot go faster than the speed of light.

 

Screw that. What if you had the energy of an infinite amount of multiverses? Would you then be able to travel in "negative" time (hence going to the past)?

 

(Not trying to troll. I think that it's a little more interesting when you can speculate what could happen in so and so circumstance rather than limiting discussion by saying that the light barrier cannot be broken.)

[Iamdan]

If you were going backwards in time, you would be timeless. Then you just have speed = distance/0

 

(inb4 divide by 0 universe exploding picture)

 

Even if we had a source of infinite power it's impossible.

[assassin_696]

Nope, as far as speed is concerned, you cannot go faster than the speed of light.

 

well, that's really a simplification of the truth. things cannot cross the boundy of the speed of light. either they've always existed above the speed of light, or below since the bing bang, just like any other mathematical limit you can approach it from either direction. As sub-lightspeed particles we'll never be able to observe above-lightspeed particles and vice versa either.

 

I though charged tachyons would emit Cherenkov radiation, lose energy and then speed up (counter-intuitively)?

 

Don't some physicists believe that the initial expansion of the universe exceeded the speed of light because there were no physical laws before there was a "physical" universe?

 

Not quite. Nothing can travel faster than the speed of light in a vacuum, but technically space itself can expand faster than light.

 

Nope, as far as speed is concerned, you cannot go faster than the speed of light.

 

Screw that. What if you had the energy of an infinite amount of multiverses? Would you then be able to travel in "negative" time (hence going to the past)?

 

(Not trying to troll. I think that it's a little more interesting when you can speculate what could happen in so and so circumstance rather than limiting discussion by saying that the light barrier cannot be broken.)

 

It might be interesting but it's completely pointless. Sorry if the laws of physics are "limiting" your discussion but those are the rules and pretending they don't exist is a waste of time. More interesting is thinking about how faster than light travel might work within the current laws of physics, see for example The Alcubierre Drive.

 

If you were going backwards in time, you would be timeless. Then you just have speed = distance/0

 

(inb4 divide by 0 universe exploding picture)

 

Even if we had a source of infinite power it's impossible.

 

Particles travelling backwards in time have been hypothesised to explain quantum entanglement effects. The laws of physics work nicely in both directions so there's no reason why you couldn't have particles travelling backwards in time, but sending a forwards travelling particles backwards in time would be impossible.

[tortilliachp]

Nope, as far as speed is concerned, you cannot go faster than the speed of light.

 

well, that's really a simplification of the truth. things cannot cross the boundy of the speed of light. either they've always existed above the speed of light, or below since the bing bang, just like any other mathematical limit you can approach it from either direction. As sub-lightspeed particles we'll never be able to observe above-lightspeed particles and vice versa either.

 

I though charged tachyons would emit Cherenkov radiation, lose energy and then speed up (counter-intuitively)?

yes. tachyons are also by definition particles already travelling faster than the speed of light :wink: tachyons may theoretically absorb negative cherenkov radiation in metamaterials, gaining anergy and then slowing down (at least that's my understanding of synthetic meta-materials).

 

I'm sure of my assertion. if you find mathetmatical physics proving me wrong though, i'd have beef with my physics professors and textbooks however :D

[assassin_696]

yes. tachyons are also by definition particles already travelling faster than the speed of light :wink: tachyons may theoretically absorb negative cherenkov radiation in metamaterials, gaining anergy and then slowing down (at least that's my understanding of synthetic meta-materials).

 

I'm sure of my assertion. if you find mathetmatical physics proving me wrong though, i'd have beef with my physics professors and textbooks however :D

 

No I agree, my point is that if you could detect Cherenkov radiation in a vacuum that would indicate that tachyons existed. Obviously that's inferring their existence, but did you mean that we can't directly see superluminal particles?

[tortilliachp]

yes. tachyons are also by definition particles already travelling faster than the speed of light :wink: tachyons may theoretically absorb negative cherenkov radiation in metamaterials, gaining anergy and then slowing down (at least that's my understanding of synthetic meta-materials).

 

I'm sure of my assertion. if you find mathetmatical physics proving me wrong though, i'd have beef with my physics professors and textbooks however :D

 

No I agree, my point is that if you could detect Cherenkov radiation in a vacuum that would indicate that tachyons existed. Obviously that's inferring their existence, but did you mean that we can't directly see superluminal particles?

 

No. i mean that since tachyons do not emit Cherenkov radiation in vacuum, they cannot be indirectly observed either (that proof is a more complex though).

 

an analogy (although completely false) is that you can't break the sound-barrier in vacuum, even if sound could propagate in vacuum, due to there being nothing to "break through" in the vacuum itself.

[assassin_696]

No. i mean that since tachyons do not emit Cherenkov radiation in vacuum, they cannot be indirectly observed either (that proof is a more complex though).

 

an analogy (although completely false) is that you can't break the sound-barrier in vacuum, even if sound could propagate in vacuum, due to there being nothing to "break through" in the vacuum itself.

 

I appreciate that it's never been observed but I don't see in principle why it couldn't happen. Could you refer me to the proof of how superluminal particles cannot be detected? I'm curious and have never explicity heard of it, and it surprises me that quite a few experiments have looked for them if it's known to be impossible.

[tortilliachp]

No. i mean that since tachyons do not emit Cherenkov radiation in vacuum, they cannot be indirectly observed either (that proof is a more complex though).

 

an analogy (although completely false) is that you can't break the sound-barrier in vacuum, even if sound could propagate in vacuum, due to there being nothing to "break through" in the vacuum itself.

 

I appreciate that it's never been observed but I don't see in principle why it couldn't happen. Could you refer me to the proof of how superluminal particles cannot be detected? I'm curious and have never explicity heard of it, and it surprises me that quite a few experiments have looked for them if it's known to be impossible.

at best, significant assumptions are made to allow vacuum Cherenkov radiation. http://prd.aps.org/abstract/PRD/v76/i2/e025024 is the best i can do in terms of articles that are available free online.

 

there are vast assumptions made in all similar articles, assumptions that cannot be controlled, only inferred.

when making assumptions, such as assuming Lorentz law needs modification at speeds close to the speed of light, you're moving in uncharted territory.

 

None of our physical theories can directly be attributed to be true above the speed of light, as no one has yet observed superluminal particles, much less verified theories above the speed of light: therefore anyone can speculate, but that's all it is.

[assassin_696]

at best, significant assumptions are made to allow vacuum Cherenkov radiation. http://prd.aps.org/abstract/PRD/v76/i2/e025024 is the best i can do in terms of articles that are available free online.

 

there are vast assumptions made in all similar articles, assumptions that cannot be controlled, only inferred.

when making assumptions, such as assuming Lorentz law needs modification at speeds close to the speed of light, you're moving in uncharted territory.

 

None of our physical theories can directly be attributed to be true above the speed of light, as no one has yet observed superluminal particles, much less verified theories above the speed of light: therefore anyone can speculate, but that's all it is.

 

I see where you're coming from, and largely agree, but is modifying the Lorentz force near the speed of light really controversial? I thought it was a fairly well accepted principle to account for the gamma function.