Keep calm, I'm objecting to the terminology. I don't see the Minkowski metric as 'absolute space-time'.altsci2 said:One needs 4-d coordinate system with Lorentz metric. May be you think it was existed before SR?
And what is in SR that above the 4-d coordinate system with Lorentz metrics? May be Lorentz metrics itself?
It is standard terminology.altsci2 said:Both Mentz and Dale objections against the term "absolute". Also they rather use the term "Minkowski space" and "Minkowski metric".
Minkowski used imaginary time and Euclidean metric. Also he did not consider arbitrary transformations of coordinates. As far as we concerned with 4-d geometry I would better refer to Riemann approach with real axes and arbitrary transformations of coordinates. We always need to start with the coordinate system with rectilinear axes and prescribed metrics (the Lorentz Metrics). This coordinate system and this metrics describe the "Space of SR". We can call it "Minkowski Space" just to honor Minkowski. If you mean that - it is ok.
I think the word you are looking for is "invariant". Here is a recent discussion on the topic.altsci2 said:About "absolute". Having Minkowski coordinate system and given a trajectory of a point particle in it (numerical description) is enough to calculate acceleration in any point that will be the same in any other coordinate system (scalar) in the same point (points survive arbitrary transformation). The acceleration will be not relative, it will be "absolute" (no other reference is necessary except Minkovski space itself).
You can't use light to detect inertial motion because it will always travel at c.Gadhav said:Some basic doubts I have are:
1) When doing thought experiment for Inertial frame moving with constant velocity and enclosed in box, when a ray of light starts, does it get detached from the box? If yes, we can detect the motion, correct?
In this situation it is better think of light as EM waves.2) When ray of light emits say from star, (and say they emit photons), the beam would diverge outwards. what happens to space between the two rays say trillion miles away from star? If there are no photons here, I should not see the star, correct?
Gadhav said:Some basic doubts I have are:
1) When doing thought experiment for Inertial frame moving with constant velocity and enclosed in box, when a ray of light starts, does it get detached from the box? If yes, we can detect the motion, correct?
Gadhav said:2) When ray of light emits say from star, (and say they emit photons), the beam would diverge outwards. what happens to space between the two rays say trillion miles away from star? If there are no photons here, I should not see the star, correct?
That post says "Here is a transform which has the relativity of simultaneity, but not length contraction or time dilation: t′=t−vx, x′=x−vt. " Actually I think that transformation does entail some time dilation, although not reciprocal. A clock at rest in the primed coordinates would run slow by a factor of 1-v^2 relative to the unprimed coordinates. On the other hand, a clock at rest in the (unique) unprimed coordinates has no dilation relative to the primed coordinates.
Mentz114 said:You can't use light to detect inertial motion because it will always travel at c.
In this situation it is better think of light as EM waves.
Gadhav said:I think my point is that if light detached from the box and box moving, it will take more time for it to travel to end and less time when coming back. Speed at which it does should not matter.
Also Whether it is photon or EM wave, they all travel in st lines and diverge so in theory there can be areas where EMwave or photon will not reach, far away from star.
Sorry but I don't think I am convinced yet why it happens.
Can you describe exactly the apparatus to detect this ?Gadhav said:I think my point is that if light detached from the box and box moving, it will take more time for it to travel to end and less time when coming back. Speed at which it does should not matter.
True, when the intensity of the light falls below the limit of detection then nothing will be seen. So what ?Also Whether it is photon or EM wave, they all travel in st lines and diverge so in theory there can be areas where EMwave or photon will not reach, far away from star.
Mentz114 said:Can you describe exactly the apparatus to detect this ?
In the section I've highlighted, what is 'v' in 'L+vt' ?Gadhav said:Let us assume that a photon leaves one end of room. Room is moving right at "v" since photon is not acquiring room's velocity, it travels L+vt in forward direction and L-vt in reverse. Since the time is different, it can be detected.
This is same as MM Experiment. I understand that this logic works for point of view of observer outside. My Q is: why cannot person inside the box detect the same. Note that if particle acquired box's speed, it would be impossible to detect it (Ex: person in car) but photon does not and that is important.
The exact concept is not going in my head.
The exact concept is what Einstein discussed in section 1 of his 1905 paper introducing SR. Please read and study that section and either tell us that the exact concept is now going in your head or tell us why you think that Einstein was wrong.Gadhav said:Let us assume that a photon leaves one end of room. Room is moving right at "v" since photon is not acquiring room's velocity, it travels L+vt in forward direction and L-vt in reverse. Since the time is different, it can be detected.
This is same as MM Experiment. I understand that this logic works for point of view of observer outside. My Q is: why cannot person inside the box detect the same. Note that if particle acquired box's speed, it would be impossible to detect it (Ex: person in car) but photon does not and that is important.
The exact concept is not going in my head.
Gadhav said:Let us assume that a photon leaves one end of room. Room is moving right at "v" since photon is not acquiring room's velocity, it travels L+vt in forward direction and L-vt in reverse. Since the time is different, it can be detected.
This is same as MM Experiment. I understand that this logic works for point of view of observer outside. My Q is: why cannot person inside the box detect the same. Note that if particle acquired box's speed, it would be impossible to detect it (Ex: person in car) but photon does not and that is important.
The exact concept is not going in my head.
Gadhav said:Let us assume that a photon leaves one end of room. Room is moving right at "v" since photon is not acquiring room's velocity, it travels L+vt in forward direction and L-vt in reverse. Since the time is different, it can be detected.
This is same as MM Experiment. I understand that this logic works for point of view of observer outside. My Q is: why cannot person inside the box detect the same. Note that if particle acquired box's speed, it would be impossible to detect it (Ex: person in car) but photon does not and that is important.
The exact concept is not going in my head.
You cannot measure the speed of light to be c in all directions. Instead, Einstein defines the speed of light to be c in all directions and then uses that to define an inertial reference frame. The sagnac effect does not apply as it is not inertial.JohnWisp said:Here is the deal.
For whatever reason, there have been many experiments that have proven no matter what you think the room is doing, the room measures c except for the Earth's rotational sagnac effect.
For example, the "room" "earth" rotates. travels around the sun, moves with the milky way and whatever else, but light still measures c in all directions as verified by GPS with the exception of the rotational sagnac effect.
These are the facts.
+
ghwellsjr said:You cannot measure the speed of light to be c in all directions. Instead, Einstein defines the speed of light to be c in all directions and then uses that to define an inertial reference frame. The sagnac effect does not apply as it is not inertial.
I'm not disagreeing with the article. We cannot use just Special Relativity to design GPS because it operates under the influence of gravity. The fact that GPS works proves that the designers made a good choice when they used both Special Relativity and General Relativity to design it. But that does not change the fact that Special Relativity defines the speed of light to be c in all directions as opposed to measuring it independent of any theory.JohnWisp said:GPS proves the speed of light is measured c in all directions except for sagnac.
That is what I said.
Are you claiming this is false? See Neil Ashby.
http://relativity.livingreviews.org/Articles/lrr-2003-1/
JohnWisp said:GPS proves the speed of light is measured c in all directions except for sagnac.
That is what I said.
Are you claiming this is false? See Neil Ashby.
http://relativity.livingreviews.org/Articles/lrr-2003-1/
Vanadium 50 said:Where does he say this? I see him state that it is defined to be c in all directions, not measured.
ghwellsjr said:I'm not disagreeing with the article. We cannot use just Special Relativity to design GPS because it operates under the influence of gravity. The fact that GPS works proves that the designers made a good choice when they used both Special Relativity and General Relativity to design it. But that does not change the fact that Special Relativity defines the speed of light to be c in all directions as opposed to measuring it independent of any theory.
What does tl;dr mean?georgir said:The whole thread is tl;dr. But to the OP - any two events that are separated far enough from each other to require a faster than light speed to connect, are simultaneous in some reference frame. Such events are called space-like separated events. It is accepted than no causal relation between such events can exist.
On the other hand, any two events that are close enough to connect with slower-than-light speed in one reference frame are also separated similarly in all other reference frames. They are not simultaneous, nor in a reversed order in any other reference frame. Such events are called time-like separated events.
http://lmgtfy.com/?q=tl;drghwellsjr said:What does tl;dr mean?
Again, we cannot measure the speed of light in any direction. We assign the speed of light to be c in all directions in any Inertial Reference Frame (IRF). Therefore, the time it takes for light to propagate from one spatial point to a second spatial point is only the same as it takes for the reflection to propagate back to the first point in an IRF in which the first spatial point is at rest because our definition of an IRF makes it so. In other IRFs moving along the direction between those two spatial points, the time it takes for the light to propagate along the same two paths in opposite directions are not equal.JohnWisp said:Yes, I realize that.ghwellsjr said:I'm not disagreeing with the article. We cannot use just Special Relativity to design GPS because it operates under the influence of gravity. The fact that GPS works proves that the designers made a good choice when they used both Special Relativity and General Relativity to design it. But that does not change the fact that Special Relativity defines the speed of light to be c in all directions as opposed to measuring it independent of any theory.
But the Op is trying to understand how light is not measured c when it is in fact measured c.
The OP thinks it should be c+v and c-v.
GPS refutes this and that is what I was posting.
One of the rules on this forum is:georgir said:http://lmgtfy.com/?q=tl;drghwellsjr said:What does tl;dr mean?
All posts must be in English. Posts in other languages will be deleted. Pay reasonable attention to written English communication standards. This includes the use of proper grammatical structure, punctuation, capitalization, and spelling. SMS messaging shorthand ("text-message-speak"), such as using "u" for "you", and "please" for "please", is not acceptable.
There is also a rule about off-topic discussions such as the one both of us are currently having. If you want, use the 'report' button on my post instead.ghwellsjr said:Please follow the rules.