- #36
GhostLoveScore
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15characters said:If the Galaxy is approaching at 0.99C and the photons at 100%C than they have separated from each other at a speed of 0.01C.
Wait, shouldn't you be adding velocities like this
15characters said:If the Galaxy is approaching at 0.99C and the photons at 100%C than they have separated from each other at a speed of 0.01C.
If the Galaxy is approaching at 0.99C and the photons at 100%C than they have separated from each other at a speed of 0.01C
GhostLoveScore said:Wait, shouldn't you be adding velocities like this?
Who needs a thought experiment? There are numerous high precision actual experiments on this point.GhostLoveScore said:If there is an light source and the object moving away from light source at 0.5c, why does the light passes by the object at the speed of light? Is there some thought experiment about this?
No. Nobody expected that result and it took a lot of experiments to make people accept it as fact. Even then, people wanted to believe that it was just a trick due to objects being compressed by traveling fast through ether. Only Einstein had enough nerve / genius to assume that the speed of light really was constant and to reach the profound conclusions that it implies. Others had done a lot of the math, but they didn't fully appreciate the consequences. There is no thought experiment to explain it. There are only thought experiments to explain the consequences of it.GhostLoveScore said:If there is an light source and the object moving away from light source at 0.5c, why does the light passes by the object at the speed of light? Is there some thought experiment about this?
##W = \frac{\frac{U+V}{C}}{1+\frac{UV}{C^2}}##GhostLoveScore said:Sorry, I meant why are velocities adding the way they are adding
According to whom?GhostLoveScore said:how could the light sent from moving object still travel at light speed?
The analogy goes further I think. It's like you're at the podium watching a sound wave generated by a race car. The speed of the sound is not [(the speed of the car) + (the speed of the sound)], the speed of the sound generated by the car travels at sound speed, about 340 m/s.PAllen said:[..] - wave theory suggested that emitter speed has no effect on signal speed. For example, this is true for sound, in the 'air frame'.
- The inability to detect absolute (inertial) motion suggested that you can't detect motion relative to a hypothetical aether (light analog of air).
Putting these together, you are led inexorably to SR. [..]
The fact that you are asking this question indicates that you really do not understand the most basic ideas of relativity. The fact that "light sent from moving object still travel at light speed", that the speed is the same in all frames of reference, is a "postulate" derived from experiment, not any calculation, and all other formulas and calculations follow from that.GhostLoveScore said:Sorry, I meant why are velocities adding the way they are adding, relativistic way - how could the light sent from moving object still travel at light speed? I know about the equation for calculating that speed, but I'm asking for more intuitive explanation, if there is one.
The assumption is that the speed of light is c, so that if the object goes at 0.5c then according to your reference system the speed difference is 0.5c.GhostLoveScore said:If there is an light source and the object moving away from light source at 0.5c, why does the light passes by the object at the speed of light?[..]
SR is partly based on Maxwell's electrodynamics, which assumes that light propagates as a wave. The light postulate summarizes a key wave characteristic: the speed of a wave is a constant, independent of the motion of the source.GhostLoveScore said:Sorry, I meant why are velocities adding the way they are adding, relativistic way - how could the light sent from moving object still travel at light speed? I know about the equation for calculating that speed, but I'm asking for more intuitive explanation, if there is one.
HallsofIvy said:The fact that you are asking this question indicates that you really do not understand the most basic ideas of relativity. The fact that "light sent from moving object still travel at light speed", that the speed is the same in all frames of reference, is a "postulate" derived from experiment, not any calculation, and all other formulas and calculations follow from that.
GhostLoveScore said:As always I'm again misunderstood. In short, no.
15characters said:Did you try the Minowski simulator?
GhostLoveScore said:I did not have time today to try it, I just came here to see if there are new posts. I will take a look at it tonight.
15characters said:The only way to understand it is to take the time to actually study the subject and actually try to learn something new rather than just asking random questions.
GhostLoveScore said:I am reading lots of different content (e-books, short articles, youtube videos, java applications)
One conceptual model that works for SR is that the car and the light travel (or perhaps one should say "propagate") through the same medium. That's one way to make sense of it.Stephanus said:[..] I still can't make out like the OP question, why the velocity addition formula should be ##W = \frac{U+V}{1+UV}##?
According to whom?
The moving object or the rest observer?
For the moving object, since there is no preferred inertia frame of reference, "the moving object" can consider itself at rest. So the light travels from it travels at ... the speed of light.
For the rest observer viewing the light sent from the moving object?The analogy goes further I think. It's like you're at the podium watching a sound wave generated by a race car. The speed of the sound is not [(the speed of the car) + (the speed of the sound)], the speed of the sound generated by the car travels at sound speed, about 340 m/s.
But the analogy stops here.
The speed of the sound wrt car is [(the speed of the sound) - (the speed of the car)]
The speed of light wrt moving object is [(the speed of light) -(the speed of the moving object)]
Is it because the car travels at the same medium and light doesn't travel at some medium?
harrylin said:One conceptual model that works for SR is that the car and the light travel (or perhaps one should say "propagate") through the same medium. That's one way to make sense of it.
Another conceptual model that works for SR is that the car and the light describe trajectories through Spacetime, interpreted as a 4D physical "medium".
There were never ending debates on this forum in which people, in vain, tried to disprove either or both interpretations, and a stop of such debates is being enforced here. Remains that you can choose the interpretation you like: whichever fits better with how your brain is wired.
You can find the debates including elaborations of how those models work by means of a search on this forum of such terms as "block universe".
15characters said:Numbers - speed of object
Light from any moving object will arrive at the observer at C. That observer will calculate the speed of light with relation to the moving object as: C minus speed of object.
Example
Light from a spacecraft heading towards Earth at 0.99c will arrive at Earth at speed C. The speed of the spacecraft is 0.99C. The speed of light is C. Therefore the speed of object with relation to the light emitted is 1C - 0.99C = 0.01C according to observers on Earth
For the comet the speed of light with relation to itself would obviously not be 0.01C, it would be C. The comet would calculate that the light arrived at Earth at 1.99C (from the comets perspective)
The formula for adding velocities is not required for the above analysis. It would be required if the comet traveling towards Earth at 0.99C fired a rocket towards Earth at 0.2C (or any velocity) relative to itself. Then the speed of the rocket relative to Earth would be calculated using the velocity addition formula.
Sources
"Spacetime Physics"
http://galileo.phys.virginia.edu/classes/252/time_dil.html
Interpretation
I don't think the special theory of relativity is matter of "interpretation". Especially if you do not understand the basics - like velocity addition. Can you explain?
For example, where you said a "medium" through which light and the car "propogate", would such a medium be analogous to the ether? How can that be "one way to make sense of" the Special Theory.
How can you say spacetime is just one of the many "conceptual model" that works with relativity and that another model that works would be one where there is a medium through which light passes (similar to ether)?
Finally, what difference does it make how one's brain is "wired"? How is that relevant to the facts? How can it be a matter of personal choice which interpretation is correct?
That would be Minkowski...15characters said:I suspect the OP knows more than it seems as they produced the formula out of nowhere.
This Minowski simulator will remove any confusion
http://www.opensourcephysics.org/items/detail.cfm?ID=11449
PAllen said:See our FAQ for how multiple interpretations such as Harrylin mentions are possible, and also the PF policy he refers to:
https://www.physicsforums.com/threads/what-is-the-pfs-policy-on-lorentz-ether-theory-and-block-universe.772224/
Well, so is the link from the FAQ list at the top of relativity forum! This was apparently recently broken. It should be fixed.pervect said:Bad link :(