Would Religion still continue if....

[Upchurch]

So if the speed of light is the MAXIMUM speed, then how can information travel back and fourth between the TWO ships which are separating at 1.4 x C? In other words, if the two ships are both flying away from the Earth at 0.7 x C (each), then they are separating at a rate of 1.4 x C.

this is only true from the point of view of the Earth frame of reference. From either ship's point of view, their relative velocities would be different and under 1.0C. I don't have time today or I'd do the math and give the actual relativistic speed, but hans is right. it has to do with length contraction and time dialation. (I'm assuming, of course, that there is no acceleration/decelleration going on.)

 

[Franko]

this is only true from the point of view of the Earth frame of reference. From either ship's point of view, their relative velocities would be different and under 1.0C. I don't have time today or I'd do the math and give the actual relativistic speed, but hans is right. it has to do with length contraction and time dialation. (I'm assuming, of course, that there is no acceleration/decelleration going on.)

The Two ships are separating at 1.4 x C, and they are still able to communicate. You don’t see a contradiction there Upchimp?

this is only true from the point of view of the Earth frame of reference. From either ship's point of view, their relative velocities would be different and under 1.0C.

… hans is right

Really? …Then why does MRC agree with me and disagree with you?

MRC:

Actually, you can show that certain incidents can be defined that move faster than light, the theoretical differential speed between your two spaceships being one example, but information still travels only at the speed C.

 

[Upchurch]

The Two ships are separating at 1.4 x C, and they are still able to communicate. You don’t see a contradiction there Upchurch?

Inertial reference frames are a basic component of the Special Theory of Relativity. If you don't get that, I don't know what to tell you. Maybe other than, read a book.

Edited to add:

From the link above

According to special relativity, no wave or particle may travel at a speed greater than the speed of light c. Therefore, the usual rules from Newtonian mechanics do not apply when adding velocities that are large enough. For example, if a particle travels at a speed v with respect to a stationary observer, and another particle travels at a speed v' with respect to the first particle, the speed u of particle two seen by the observer is not v + v' as would be the case in Newtonian mechanics, but rather

u = (v + v') / (1 + (v v') / c^2)

Taken from the POV of one of the ships, the speed of the Earth, v, is 0.7c and the speed of the other ship, v', from the POV of the Earth is 0.7c. Everything else is a constant, so you can determine how fast the ships are actually traving apart from each other, u.

u = (0.7c + 0.7c) / (1 + (0.7c 0.7c) / c^2)

u = (1.4c) / (1.49)

u = 0.940c (approximately)

So, the spaceships have a relative velocity of 0.94c, not 1.4c

 

[Franko]

Franko:
Suppose that at some point in the future Humans are capable of building a spacecraft that can travel of 70% the speed of Light. But imagine that this is a spacecraft built to send Human colonists to another planet, so they build this craft from a large rocky asteroid captured from the solar system.

Now suppose that they build Two of these “spacecraft” – both capable of traveling 70% the speed of light …

… and they send them off in opposite directions. From the POV of the crew on either of these crafts they are standing on a “stationary planetary body” (like the Earth). But since BOTH ships are traveling away from the Earth at 70% the speed of light, wouldn’t they being traveling at 140% the speed of light away from each other? In other words from a person on one of the asteroids, wouldn’t it appear that the other asteroid was moving away from him at a speed beyond what is “allowable” by General Relativity?

Or think of it this way … suppose you have two flashlights, and you “glue” the back ends together so that the beams of lights are shining in opposite directions. From the “POV” of the photons in one beam, aren’t the photons in the opposite beam moving away at twice the speed of light?

MRC:
The very basic of Relativity is that the speed of light is the maximum you can observe, no matter the conditions. If you are in a spaceship going 70% lightspeed and shine a light forward, you will see it leaving you at lightspeed, but the the stationary observer, it will still move only at lightspeed, not 170% lightspeed. Time dilation is the key to the answer.

Actually, you can show that certain incidents can be defined that move faster than light, the theoretical differential speed between your two spaceships being one example, but information still travels only at the speed C.

Franko:
Right, but I thought that according to GR Nothing could move faster than the speed of light relative to any other object? And if information can’t travel faster than the speed of light, then how come the one ship could relay a signal back to the earth, and then the earth could relay the signal on to the second ship? You just acknowledged that the ships would be separating faster than the speed of light, yet they are still able to communicate?

Can you explain this apparent discrepancy for me?

MRC:
Lets assume that ship A sends a message towards B. For simplicity, lets assume it's just a green laser beam. The laser beam will move at the speed C, but because ship A will move away from it at 0.7C, it will be strongly red-shifted (like a police siren when the squad car speeds by, it is called Doppler shift). To the occupants of ship A it will seem normal because their time will run correspondently slower.

Sooner or later the laser beam travelling at C will catch up with ship B, and since B is running away from it at 0.7C, it will be further red-shifted (way into infrared), but this will not be visible to the occupants of Ship B, because their time-dilution will cancel out this extra red-shift. So what they will see is a laserbeam redshifted from being sent backwards from a ship going away at 0,7C; exactly the same as a stationary observer would observe.

However, the stationary observer might calculate the time taken for the laser beam to traverse from ship A to ship B and realize that their speed difference was 1,4C.

Franko:
Exactly.

So if the speed of light is the MAXIMUM speed, then how can information travel back and fourth between the TWO ships which are separating at 1.4 x C? In other words, if the two ships are both flying away from the Earth at 0.7 x C (each), then they are separating at a rate of 1.4 x C.

So if light (information) only travels at 1.0 x C, then how can the Two ships communicate? Isn’t 1.0 less than 1.4?

Upchurch here is where the discussion stands. Am I understanding your correctly? Are you disagreeing with me and MRC that the two ships can be moving away from each other at 1.4 x C?

Please state specifically your precise point of disagreement, and the specific reason(s) you disagree.

 

[Upchurch]

Upchurch here is where the discussion stands. Am I understanding your correctly? Are you disagreeing with me and MRC that the two ships can be moving away from each other at 1.4 x C?

Edited my post while you were posting. see my last post.

BTW, I always feel good when I can bring a little math into a philosophical argument. Warms my heart.

 

[MRC_Hans]

The Two ships are separating at 1.4 x C, and they are still able to communicate. You don’t see a contradiction there Upchimp?

This is the tricky thing about relativism. There is no contradiction, and I really think my explanation showed quite well what happens. The crucial point is that the lightwave transmitted backwards from ship A moves at the speed of light, both from the POV of the ship and a stationary observer.

But the same would be true of sound waves. Imagine two aircraft flying away from each other each going MACH 0,7. Plane A fires a gun, and the sound travels towards plane B at MACH 1, eventually overtaking it and theoretically audible on board. Only here the full doppler shift would be observable, because there is no time dilation.

You could even make this experiment: Two ships are sailing in opposite directions away from each other, each doing 7 knots. Ship A lowers a launch which heads for ship B. The launch can make 10 knots. Despite the separation rate of the ships being 14 knots, the launch has no difficulty reaching ship B. It can also sail back to ship A.

It's really quite simple



Really? …Then why does MRC agree with me and disagree with you?

Why should it bother him? But in this case it is not true. I referred to certain conditions where you can define an EVENT that moves faster than light. But an event is not a physical thing.

OK; since I stuck my head out on C+ events, I'd better put up:

Imagine a wave nearing a beach. If it moves towards the beach at a alightly different angle than 90deg, one end of the wave will hit the beach first, and the event of the wave hitting the beach will travel along the beach as more parts of the wave roll in. This event will travel much faster than the wave. You can sometimes observe this in reality, the speed of the event can be appr. the speed of sound, and if you stand at the end of the wave that hits last, the sound of the wave hitting will reach you as a single boom.

Of course, the same thing can be imagined when a light pulse reaches some surface slightly off-angle. The event of the pulse front hitting the surface travels perpendicular to the light beam, and at a speed that can be many times the speed of light.

Other experiments can be made to show similar effects.
This is mainly an academic exercise with little practical purpose.

Hans

 

[Upchurch]

Upchurch here is where the discussion stands. Am I understanding your correctly? Are you disagreeing with me and MRC that the two ships can be moving away from each other at 1.4 x C?

Please state specifically your precise point of disagreement, and the specific reason(s) you disagree.

Sorry, I realized I didn't actually answer the question.

Yes, I disagree. The ships are not moving apart at 1.4c. The ships are moving apart at 0.94c in each ship's frame of reference as shown above. I hope the above calculation is a specific enough reason for why I disagree.

Sorry for any confusion

 

[Franko]

So Upchurch, according to You, if we have two ships flying in opposite directions then they can't go faster than half the speed of light (each)?

 

[Franko]

MRC:
This is the tricky thing about relativism. There is no contradiction, and I really think my explanation showed quite well what happens. The crucial point is that the lightwave transmitted backwards from ship A moves at the speed of light, both from the POV of the ship and a stationary observer.

But the same would be true of sound waves. Imagine two aircraft flying away from each other each going MACH 0,7. Plane A fires a gun, and the sound travels towards plane B at MACH 1, eventually overtaking it and theoretically audible on board. Only here the full doppler shift would be observable, because there is no time dilation.

You could even make this experiment: Two ships are sailing in opposite directions away from each other, each doing 7 knots. Ship A lowers a launch which heads for ship B. The launch can make 10 knots. Despite the separation rate of the ships being 14 knots, the launch has no difficulty reaching ship B. It can also sail back to ship A.

It's really quite simple

Actually wouldn’t it be more like, we have an asteroid, and we have another asteroid moving away at the rate of 1.4C, and we have a mini-space ship that only travels at 1.0C and somehow it is able to fly between the two asteroids?

 

[Upchurch]

So Upchurch, according to You, if we have two ships flying in opposite directions then they can't go faster than half the speed of light (each)?

Well, first, it's not according to me, it's according to SR. I can't claim credit for it, just for using it.

Second, The only restriction on speed is c, not 0.5c. In the above example, each ship is going 0.7c from the Earth reference frame, but from each ship's reference frame the other ship is moving at 0.94c.

See, the crux of it is that you have to specify what reference frame you are using. You can't use the Earth's reference frame with talking about the relative velocity of two objects that aren't in the Earth's reference frame, which is what you're trying to do when you say that the ships are moving apart at 1.4c. The Earth's reference frame is irrelevant to the relative speed between the two ships. The only two reference frames that matter of that of the ships.

 

[Franko]

Franko:
So Upchurch, according to You, if we have two ships flying in opposite directions then they can't go faster than half the speed of light (each)?

Upchurch:
Well, first, it's not according to me, it's according to SR. I can't claim credit for it, just for using it.

Second, The only restriction on speed is c, not 0.5c. In the above example, each ship is going 0.7c from the Earth reference frame, but from each ship's reference frame the other ship is moving at 0.94c.

If you and I are traveling at opposite directions at 210,000 km/sec (0.7 x C – separating at 410,000 km/sec) then we are separating faster than the speed of light, are we not?

See, the crux of it is that you have to specify what reference frame you are using. You can't use the Earth's reference frame with talking about the relative velocity of two objects that aren't in the Earth's reference frame, which is what you're trying to do when you say that the ships are moving apart at 1.4c. The Earth's reference frame is irrelevant to the relative speed between the two ships. The only two reference frames that matter of that of the ships.

So are you also claiming that when light rays leave the Sun on opposite sides that these light rays (photons) are actually only moving at 0.5 x C, because they cannot be separating at a rate above 1.0xC total? I thought that it took light 8 minutes to reach the Earth from the Sun (the Earth is 8 “light minutes” distant from the Sun), are you claiming that it actually takes 16 minutes for the Sun’s light to reach the Earth?

 

[Stimpson J. Cat]

Franko,

You are making a fool of yourself again. What Upchurch has described is how SR works. This has been demonstrated extensively through empirical testing. It is clear that you don't have any idea what you are talking about. This stuff is covered in any introductory text on the subject. Why don't you try learning about a subject, before you presume to tell people who have studied it extensively that they are all wrong?

Dr. Stupid

 

[Upchurch]

If you and I are traveling at opposite directions at 210,000 km/sec (0.7 x C – separating at 410,000 km/sec) then we are separating faster than the speed of light, are we not?

Nope. If we are each traveling in opposite directions at 0.7c from the Earth, then we are traveling at 0.94c from each other. (You did read my calculation above, right? You understand Relativity, right?)

There is no absolute inertial reference frame. Speed is relative to what you're referencing it from.

So are you also claiming that when light rays leave the Sun on opposite sides that these light rays (photons) are actually only moving at 0.5 x C, because they cannot be separating at a rate above 1.0xC total?

Nope again. I'm claiming that while the photons in each beam are traveling at 1c from the sun, they are also traveling at 1c from each other. Let's do the math:

u = (v + v') / (1 + (v v') / c^2)

where:
v = the relative speed of one photon from the sun = 1c
v' = the relative speed of the one photon from the sun = 1c
u = the relative speed of each photon from each other = ?

u = (1c + 1c) / (1 + (1c 1c) / c^2)

u = (2c) / (2)

u = 1c

So, even though each photon is traveling 1c relative to the sun, they are also traveling 1c relative to each other.

 

[Upchurch]

What Upchurch has described is how SR works.

Thanks, Doc. SR/GR was my fav in college but it's been a while and it's nice to have verification that I'm not totally mis-applying the concepts here.

 

[whitefork]

Well, this is almost as good as the theory of gravitation as put forth in the Nothing thread.

Either move it to Science, or pass me some popcorn. Or both.

 

[Franko]

Franko:
If you and I are traveling at opposite directions at 210,000 km/sec (0.7 x C – separating at 410,000 km/sec [should have been 420,000km/sec]) then we are separating faster than the speed of light, are we not?

Upchurch:
Nope. If we are each traveling in opposite directions at 0.7c from the Earth, then we are traveling at 0.94c from each other. (You did read my calculation above, right? You understand Relativity, right?)

There is no absolute inertial reference frame. Speed is relative to what you're referencing it from.

Right, and if I am an observer on the EARTH (Earth is my “Relative” frame of reference), then I perceive the one ship traveling “West” away from me at 210,000 km/sec, and when I look in the opposite direction (“East”) I perceive the other ship traveling away from me at 210,000 km/sec IN THE OPPSITE DIRECTION OF THE FIRST SHIP! In other words from my perspective aren’t the two ships traveling away from each other at a rate Faster than the speed of light?

Upchurch: (A-Theist)
Nope. If we are each traveling in opposite directions at 0.7c from the Earth, then we are traveling at 0.94c from each other. (You did read my calculation above, right? You understand Relativity, right?)

So if there are two photons being simultaneously emitted from the surface of the sun in opposite directions then you are claiming that they are moving apart from each other at less than 2xC? Does that mean it takes photons longer than 8 minutes to go from the Sun to the Earth, because I am fairly certain the sun emits photons in ALL directions ALL the time?

Upchurch: (A-Theist)
Nope again. I'm claiming that while the photons in each beam are traveling at 1c from the sun, they are also traveling at 1c from each other. Let's do the math:

u = (v + v') / (1 + (v v') / c^2)

where:
v = the relative speed of one photon from the sun = 1c
v' = the relative speed of the one photon from the sun = 1c
u = the relative speed of each photon from each other = ?

u = (1c + 1c) / (1 + (1c 1c) / c^2)

u = (2c) / (2)

u = 1c

So, even though each photon is traveling 1c relative to the sun, they are also traveling 1c relative to each other.

So if the photons are traveling at 300,000 km/sec each, then in 10 seconds how far apart from the Sun will each photon be, and how far part from each other will each photon be?

I would say that in 10 seconds the two photons will each be 3,000,000 km from the Sun, and 6,000,000 km from each other. What EXACTLY are You claiming?

 

[Franko]

Stimpson: (A-Theist)
You are making a fool of yourself again. What Upchurch has described is how SR works. This has been demonstrated extensively through empirical testing. It is clear that you don't have any idea what you are talking about. This stuff is covered in any introductory text on the subject. Why don't you try learning about a subject, before you presume to tell people who have studied it extensively that they are all wrong?

I’m simply asking some basic questions Stimpson. I don’t see why you are getting so worked up, but I am touched that you are so concerned about my reputation.

whitemeat: (A-Theist)
Well, this is almost as good as the theory of gravitation as put forth in the Nothing thread.

Either move it to Science, or pass me some popcorn. Or both.

Damn, for a bunch of nitwits who claim to understand QM so well this thread seems to be making a lot of A-Theists figgity …

 

[Upchurch]

I'm going to break this up more than usual, because you're mixing frames:

Right, and if I am an observer on the EARTH (Earth is my “Relative” frame of reference),

When you say it's relative, you have to say what it's relative to.

then I perceive the one ship traveling “West” away from me at 210,000 km/sec,

the relative speed between you and the "west" ship.

and when I look in the opposite direction (“East”) I perceive the other ship traveling away from me at 210,000 km/sec

the relative speed between you and the "east" ship.

IN THE OPPSITE DIRECTION OF THE FIRST SHIP!

In this specific case, the direction is the same for all frames of reference, but they could be different if moving in anything other than one dimension.

In other words from my perspective aren’t the two ships traveling away from each other at a rate Faster than the speed of light?

The question you're asking is what is the relative speed between the east and west ships. You're trying to make it a three frame problem when speed is only applicable between two frames. with the three frames you've given, you can only talk about the speeds between each set of frames. However, given SR, we can from one frame, calculate the relative speeds between any other set of frames, given the relative speeds of each frame to the first frame.

So if there are two photons being simultaneously emitted from the surface of the sun in opposite directions then you are claiming that they are moving apart from each other at less than 2xC?

I just showed they are moving apart at half that speed above. Do you see an error in my math?

Does that mean it takes photons longer than 8 minutes to go from the Sun to the Earth, because I am fairly certain the sun emits photons in ALL directions ALL the time?

Well, I know that 8 minutes is an approximation, but no it doesn't take longer than that approximation. And I am also fairly certain that the sun emits photons in all directions at all times.

So if the photons are traveling at 300,000 km/sec each, then in 10 seconds how far apart from the Sun will each photon be, and how far part from each other will each photon be?

Hm... Interesting question, which is actually beyond the scope of SR. Due to length contraction, one could approximate through limits that, from each photon's frame of reference, the relative velocity between the two photons is 1c. Special Relativity calculations of length contraction only work for velocities less than 1c. You can make an approximation using limits, however. So, from the photon's frame of reference, after "10 seconds" (I'm not sure that's valid to say), the photons would be 0 light seconds apart. Again, that's a tentative answer based on incomplete information.

I would say that in 10 seconds the two photons will each be 3,000,000 km from the Sun, and 6,000,000 km from each other. What EXACTLY are You claiming?

I agree that they would be an amount of km greater than zero from the sun, but I can't say what they would be from each other, as per above.

 

[Upchurch]

Either move it to Science, or pass me some popcorn. Or both.

Isn't it amazing how philosophical discussions about the nature of the universe always seem to come back to science? How do you differentiate the two?

I prefer butter on my popcorn, please.

 

[LucyR]

u = (0.7c + 0.7c) / (1 + (0.7c 0.7c) / c^2)

u = (1.4c) / (1.49)

u = 0.940c (approximately)

So, the spaceships have a relative velocity of 0.94c, not 1.4c

Upchurch,

I have already demonstrated this in an earlier post in this thread. However, I agree that it probably doesn't hurt to go through it again.