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Photon path ..
#11
(05-11-2016, 01:13 PM)ALT Wrote: You said;
Train moving, target moving (say, target something inside the train) -> hit. 
1) You are saying that the photon will hit the receptor directly above it.
2) You are saying (remember, no immediate observer) that the receptor / computer will later report to me a hit.
3) Therefore you are saying that the photon IS influenced by the horizontal (transverse) movement of the photon emitter.

Yes. As for every lower than c velocity too.  For much lower than c  the velocity would be simply the sum would be simply the sum of the velocity of the thing (not photon) at rest and the velocity of the train. 

Note also that the guy at rest could have send into this different direction a photon too.  It would, once directed into the same direction, move with the same speed, the speed of light.  But there would be a difference - because the move at different speed, there would be a Doppler effect, a shift in the frequency.  If they would, say, use the same red laser pointer, the light received would be slightly different in color.
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#12
ALT wrote:

Oh, BTW, secur, earlier you said;

But (as Schmelzer explained) the vector addition is relativistic, so it winds up traveling orthogonally towards the target slower by sqrt(1 - v^2/c^2). So it will miss, by falling short.

If I'm reading that correctly, you are saying that it WILL miss the target. And note, I have never said anything about any other target - only the one, orthogonal to and directly above, the emitter.
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BTW my "quote" button isn't working - got to read the help pages :-)

As explained in my last post, I was wrong when I said "miss"; got confused by Schmelzer's comment re. "other target". But now we're all on the same page, the post above is perfectly clear. Sorry for the confusion.
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#13
The "quote" button is if you want to quote from several posts in one reply. Then you press the "quote" in all of them and then press the "New Reply" button. Or the "Reply" button of the last you want to quote.

If you want to answer only a single post, "Reply" will do the job.
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#14
Thank you both for your patience and those clarifications. Back soon to continue.
Note, I am not saying for sure one thing or the other (hit or miss) - I simply don't know. But my enquiry now focuses on;

Why is the photon not effected by the rectilinear motion of the emitter (always goes at c) but IS effected by the transverse motion of same.

But I'm typing this during work at the moment. Allow me to put my dim thoughts together and post them later :-)
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#15
The photon is effected by the motion of the emitter. But this effect is via the Doppler effect, which changes wave length (frequency), and via the direction of the light ray. The speed of light is always the same.
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#16
(05-12-2016, 05:48 AM)Schmelzer Wrote: The photon is effected by the motion of the emitter. But this effect is via the Doppler effect, which changes wave length (frequency), and via the direction of the light ray.  The speed of light is always the same.

I accept that the photon will always travel at c.

I accept that it may be (red ?) shifted by the Doppler effect. This point is moot in my thought experiment however, as I have removed any observer, and the photo receptor will register and subsequently report a hit regardless of colour, (or a miss if no hit). Thus I have now dispensed with the the Doppler effect as well.

Let's not forget - a REAL thing happens - a photon is fired and it either hits or misses the receptor, regardless of whether it ended up a rosier shade of pink.

So I am no closer to understanding HOW the photon is caused to have the emitters transverse motion.

It seems to me that the single photon has only one point of origin (the emitter tip) and only one direction of travel from that point in the instant it is emitted and only one trajectory FROM that instant onwards, which is rectilinear to the emitter. Thus, I'm contmplating that as the receptor is moving to the right, it moves away from the photons one and only path and the photon misses it.

If something causes it (a massless particle) to also move sideways (like the bullet) in order to hit the receptor, what IS that something ? How does it ... "get pushed sideways" ?
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#17
Let's create the photon with a direction in the following way: Some explosion which creates light at the center of a sphere in all directions, and a small hole in the sphere. With this construction, it obviously matters if the sphere moves or not. Because the hole has moved some distance, together with the whole sphere (together with the train). You can invent something else which directs the light into some direction, but I see no reason to expect anything different. Anyway, we have the very simple equivalence principle argument, the one from the begin of my first answer, it will work also for quite complex constructions.
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#18
ALT: I'm contmplating that as the receptor is moving to the right, it moves away from the photons one and only path and the photon misses it.

But that's not what Special Relativity says, as we've pointed out. Here's a ref from Wikipedia, "Special Relativity",

"In the frame where the clock is at rest (diagram at right), the light pulse traces out a path of length 2L and the period of the clock is 2L divided by the speed of light. From the frame of reference of a moving observer traveling at the speed v relative to the rest frame of the clock (diagram at lower right), the light pulse traces out a longer, angled path."

This refers to Einstein's famous light-clock on a train and it says "angled path". Check that page, and thousands more like it. Contemplate the "very simple equivalence principle argument" (as Schmelzer says).

After doing so, two questions:

1. Do you believe SR says that the photon is affected by the transverse motion?
2. Do you believe SR is wrong?

I'm supposing your answers are "yes" and "yes" - i.e. you think SR is wrong.

Now, doubting theory is Ok - I do it all the time - but surely you will agree, you can't doubt experimental observations. If Mother Nature sends photons out with transverse motion, there's no point in arguing with her.

So here's what you must do: find experimental evidence that proves SR is right (or, not). Unfortunately I can't help you with that. I looked around on the net (and rummaged through my memory) and can't find any experiments clearly demonstrating this exact phenomenon (lots of thought experiments, but they don't count).

When you find it, please tell me about it, I'd like to see it myself! No theory, not even an Einstein paper that's been approved by 4 generations of physicists, means anything compared to one experimental demonstration.

Moving on ...

As Schmelzer says, if you imagine the photon goes through a hole, or slit, or rifle barrel (as rjbeery mentioned), it's clear that it must go at an angle. But I bet you will continue to ask: forget the slit, why should it be angled?

On Physics Forums, Nugatory once said, paraphrasing: "light behaves as a wave when traveling, as a photon when emitted and absorbed". That's a good rule of thumb. Applying it to this issue: during the process of emission it behaves "like a rifle bullet". After being emitted at an angle, it travels like a wave.

That brings up another recommendation: go ask PF if they know of any experimental demonstration. Someone there probably does.

ALT: If something causes it (a massless particle) to also move sideways (like the bullet) in order to hit the receptor, what IS that something ? How does it ... "get pushed sideways" ?

First, "massless" isn't relevant. A photon has momentum, that's what counts. Second - it "gets pushed sideways" by the same effect that applies to a rifle bullet: vector addition of velocities. If you want a deeper reason than that, it would be "inertia". A deeper reason than that: I don't think there is any, known to modern science. That's just the way nature works (Assuming it does.)

BTW the light is blue-shifted not red-shifted. So it won't be a "rosier shade of pink", rather a "lovely sky blue" :-)

Finally ... People here have told you what SR says. If you think they're wrong, why waste any more of your time? But assuming you agree we're right but SR is wrong: well, we're not experimentalists. I certainly am not in a position to get an emitter up near the speed of light and check how the photon behaves. So in that case also: there's nothing left to debate. Go look for experimental evidence. Let me know what you find.
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#19
Thanks both for the above replies. I will respond in the next day or two.
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#20
Secur;

My hand help pocket laser, sends photons out towards my back fence with precise direction. A much larger and more complex laser that I've seen operate in a civil works projects, does the same - often over kilometres. Therefore secur, those photons behaving as waves while travelling, does no violence to the fact that, as you said, they behave like particles when emitted and absorbed. Correct me if I'm wrong, but this says to me that their path is best described as a vector - you used that term yourself.

You said; it "gets pushed sideways" by the same effect that applies to a rifle bullet:

Does it ? I don't know. This is the crux of my enquiry. I think  as light travels at c independent of the speed of the source from the instant it is emitted and for it's history thereafter, the instant my photon is emitted, it will indeed travel at c in the direction it WAS emitted, independent of the motion of the emitter.

Put it this way - if my emitter had rectilinear motion at 1/2 c, we would not add this to c and say the photon is travelling at 150% c. So why then, add the transverse motion ? Why does it get pushed sideways but not forward ? After all, there would be much more forward push than sideways push in this case.

To quickly answer your other points, although they are somewhat off topic;


1. Do you believe SR says that the photon is affected by the transverse motion?


From my vague knowledge of SR and from what you and others have said here, I can conclude, yes, SR does say that.

2. Do you believe SR is wrong?

I don't know, but would speculate - probably. Given that all knowledge is provisional and not final. But there is another, more compelling reason for my suspicion. It is the fervour and virtual religiosity with which it is defended.  A quick story .. I remember once in another science forum I was making similar enquiries, and one relativity expert screamed at me ..

YOU ARE TRYING TO DETHRONE EINSTEIN !!!

Well, damn it - I never knew that he was enthroned in the first place.

More to the point .. I simply don't care if SR is wrong or not. If it WAS wrong, it would be replaced by knowledge that was OK for a while - though equally provisional. The flat earth and the geocentric universe was OK for a while too.

In your last paragraph you asked me 'why waste your time' ? Well, I don't think I am. I find this a fascinating field of enquiry, and great grey matter exercise. Better than doing crosswords, anyway :-)

Evidence ? Experiment ? I have none. This is just my thought experiment. Does a photon leave the laser tip instantaneously and at full c and therefore unaffected by the emitters motion, or does it take some time to reach c (no matter how minute) and therefore defeat the c constant itself ?

Schmelzer ..
Let's create the photon with a direction in the following way:  Some explosion which creates light at the center of a sphere in all directions,  and a small hole in the sphere. With this construction, it obviously matters if the sphere moves or not.  Because the hole has moved some distance, together with the whole sphere (together with the train).  You can invent something else which directs the light into some direction, but I see no reason to expect anything different.  Anyway, we have the very simple equivalence principle argument, the one from the begin of my first answer, it will work also for quite complex constructions.

Wiki ..
In the physics of general relativity, the equivalence principle is any of several related concepts dealing with the equivalence of gravitational and inertial mass, and to Albert Einstein's observation that the gravitational "force" as experienced locally while standing on a massive body (such as the Earth) is actually the same as the pseudo-force experienced by an observer in a non-inertial (accelerated) frame of reference.


Can you please explain how the 'equivalence principle arguement' specifically relates to my thought experiment ?

Your sphere / hole scenario is interesting and I will need to think on it awhile. I hope you also read my reply to secur as well, in the meantime.
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