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.
georgir said: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.
How was I supposed to know you weren't following the rules? I thought, like justin, "you mashed the keyboard by accident" and I was simply bringing it to your attention so you could correct it. Instead, you put the burden of understanding your keyboard shortcuts on all your readers. You didn't even explain it simply. You made me go to a link which ended by saying "Was that so hard?". The question is: Is it so hard for you to type normal English? Instead, you prefer to save a couple seconds of your own time and waste a lot of time for everyone else. Please follow the rules and spend a tiny little bit more of your time writing out normal plain English so that we can all read it clearly instead of taking our time to go search on Google or elsewhere for what we assume is something that should make sense.georgir said: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.
ghwellsjr said: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.
There is no measurement, independent of previously assigning or assuming the two propagation paths to yield the same time, that will determine that they take the same time.
I don't know why this is so hard for you to accept. If you just think about Relativity of Simultaneity, you can easily see that the time it takes for light to go in two directions between two spatially separated points takes different times in different frames. Look at this post I just made for you in another thread:
https://www.physicsforums.com/showpost.php?p=4341630&postcount=30
In the first IRF diagram where the blue twin is not at rest, the time it takes for his signal to propagate to the red twin is not the same as the time it takes for the light to reflect back but in the second IRF diagram where the blue twin is at rest, the two times are equal.
JohnWisp said:Your statement above contradicts GPS. We measure c for triangulation (all directions), that's why it works.
Vanadium 50 said:You keep saying this. It is not true. (And the reference you claimed supported this said nothing of the sort, which is rather annoying).
The speed of light is assumed (actually, defined) to be the same in all directions, not measured to be the same. Indeed, in a world with length contraction and time dilation, it is impossible to measure the one-way speed of light.
In 1889, a new international prototype was made of an alloy of platinum with 10 percent iridium, to within 0.0001, that was to be measured at the melting point of ice. In 1927, the meter was more precisely defined as the distance, at 0°, between the axes of the two central lines marked on the bar of platinum-iridium kept at the BIPM, and declared Prototype of the meter by the 1st CGPM, this bar being subject to standard atmospheric pressure and supported on two cylinders of at least one centimeter diameter, symmetrically placed in the same horizontal plane at a distance of 571 mm from each other.
The 1889 definition of the meter, based upon the artifact international prototype of platinum-iridium, was replaced by the CGPM in 1960 using a definition based upon a wavelength of krypton-86 radiation. This definition was adopted in order to reduce the uncertainty with which the meter may be realized. In turn, to further reduce the uncertainty, in 1983 the CGPM replaced this latter definition by the following definition:
The meter is the length of the path traveled by light in vacuum during a time interval of 1/299 792 458 of a second.
Note that the effect of this definition is to fix the speed of light in vacuum at exactly 299 792 458 m·s-1. The original international prototype of the meter, which was sanctioned by the 1st CGPM in 1889, is still kept at the BIPM under the conditions specified in 1889.
When Einstein formulated his second postulate, it had nothing to do with the value of c or the fact that it is measured to be a constant. This measurement is always a two-way or a round-trip measurement. Rather, his second postulate has to do with the propagation of light in any direction or to state it another way, whenever anyone in an inertial state measures the two-way speed of light, we can define the times it takes for each "half" of the trip to be exactly half of the total round-trip time. Unless we make an arbitrary definition like this, we have no way of knowing how to partition the two times.pervect said:While the speed of light _is_ currently defined to be equal to "c", it wasn't ALWAYS this way.