# The Naked Scientists Forum

### Author Topic: Why do photons have the same speed regardless of the velocity of their source?  (Read 12881 times)

#### puppypower

• Hero Member
• Posts: 562
• Thanked: 43 times
##### Re: Why do photons have the same speed regardless of the velocity of their source?
« Reply #100 on: 28/03/2016 12:08:42 »
Photons have two aspects. On the one hand, they travel at the speed of light which is the same in all references. Photons also express  wavelength and frequency, which are dependent on inertial reference. A moving source can impact wavelength/frequency, since the inertial reference changes, but it does not impact the speed of light. These are two different legs of the photon.

One leg of the photon is always in the ground state of the speed of light, with this ground state the same for all inertial references. The other leg is in inertial reference and will therefore change with reference. If we were to travel at the speed of light, we would not be able to see the all the variety of wavelength, since space-time will be contracted to a point-instant. Wavelength and frequency differentiation is an artifact of inertial reference and space-time.

Because of the two legs, a potential is set between the ground state at C, which does not see any variety in terms of wavelength and frequency; unbiased reference for all, and the wavelength and frequency, determined by space-time and inertial reference. A tug of war between the two; inertial and the C-ground state, results in the wave nature of photons. If we alter inertial reference, the parameters of the tug of war change, thereby altering the wavelength and frequency seen in inertial reference. The ground state never changes.

The red shift of the universe reflects that the C ground state wins all the tug of wars over time. The energy value of photons lose potential to the ground state and red shift.

As an analogy say we have a series of different weights hanging from a series of standard springs. Gravity defines the ground state common for all the springs; how they will hang at steady state. If we start at the top of all the springs and let them all fall, they will each vibrate; wavelength and frequency, based on the potential between the common ground state and the weight/tension in each spring.

Say we had one static spring/weight and we conserve the energy from one vibrating spring and transfer this energy to the static spring. The frequency will change base on its weight. Weight itself is dependent on the ground state of gravity.
« Last Edit: 28/03/2016 12:21:31 by puppypower »

#### jeffreyH

• Global Moderator
• Neilep Level Member
• Posts: 3932
• Thanked: 55 times
• The graviton sucks
##### Re: Why do photons have the same speed regardless of the velocity of their source?
« Reply #101 on: 28/03/2016 14:26:19 »
The more important question is how the shift in wavelength fits in with Lorentz transformations, time dilation and length contraction. Is there an inequality in the effects on particles with rest mass and massless bosons. This is obviously true simply because of the speed of light. Is this hiding an important inequality?

#### jeffreyH

• Global Moderator
• Neilep Level Member
• Posts: 3932
• Thanked: 55 times
• The graviton sucks
##### Re: Why do photons have the same speed regardless of the velocity of their source?
« Reply #102 on: 28/03/2016 14:32:26 »
Near the event horizon of a black while fermions are doomed photons can still happily escape. This is where the hidden inequality will be most apparent.

#### timey

• Neilep Level Member
• Posts: 1309
• Thanked: 9 times
##### Re: Why do photons have the same speed regardless of the velocity of their source?
« Reply #103 on: 28/03/2016 15:29:21 »
The more important question is how the shift in wavelength fits in with Lorentz transformations, time dilation and length contraction. Is there an inequality in the effects on particles with rest mass and massless bosons. This is obviously true simply because of the speed of light. Is this hiding an important inequality?

Jeff - clearly you are firing on all cylinders... :)

At two moments in each cycle of the audio feeding into the speaker, while the speaker is moving upwards at about 10.6258 mm/second, the gamma rays will have just the right frequency to be absorbed by Fe57 in the detector. For these moments, the output of the scintillation counter drops, because more of the gamma rays are being absorbed.
At these moments, the Doppler shift and gravitational shift cancel, and you get the same result as if you conducted the experiment horizontally.

Gamma Rays emitted near the highest point of the speaker cone travel many wavelengths less distance than gamma rays emitted near the lowest point of the speaker cone. But the effect of gravitational shift, which happens over 22.5m dwarfs the effect of the speaker moment (which is probably 0.01m).

Yes - there is a variance in the distance between the back and forth motion of the speaker cone.  The photon that is emitted from the speaker cone from the forward position of the cone, takes a shorter amount of 'time' to travel to the receiver than the photon that is emitted from the backward position of the speaker cone.  This constitutes a 'time' variance in the test signal.

How does a time variance of this magnitude exist within the gravitational shift over 22.5 metres?

#### alancalverd

• Global Moderator
• Neilep Level Member
• Posts: 4729
• Thanked: 156 times
• life is too short to drink instant coffee
##### Re: Why do photons have the same speed regardless of the velocity of their source?
« Reply #104 on: 28/03/2016 16:17:10 »
The photon that is emitted from the speaker cone from the forward position of the cone, takes a shorter amount of 'time' to travel to the receiver than the photon that is emitted from the backward position of the speaker cone.
But remember that velocity is the time derivative of position. The cone isn't moving at either the forward or backward position, so there is no Doppler shift.

#### timey

• Neilep Level Member
• Posts: 1309
• Thanked: 9 times
##### Re: Why do photons have the same speed regardless of the velocity of their source?
« Reply #105 on: 28/03/2016 16:58:10 »
Alan - The info that Evan quoted stated that the gravitational shift was cancelled out when exactly the correct 'back and forth' motion of the speaker was matched by the correct position of 1 photon being emitted at 1 distance, and 1 photon being emitted at a different distance... (It didn't quite say this, but this 'is' what it meant, because frequency is the result of oscillation)

I don't understand your fixation with the terminology Doppler shift... :(
The experiment states that a Doppler shift was created to measure the gravitational shift.  What more do you want me to say about it?

My observation is that 'relative motion' was used in the test signal to measure gravitational shift over a 'fixed' distance.  The relative motion was caused by, what looks very much to me, like a 'time delay'.  The light emitter was being reverberated.

(Edit:  The noise from the speaker will be having no effect on the light whatsoever - it is the noise that drives the speaker, and hence the subsequent oscillations in the speaker cone, upon which the light emitter is mounted, that is creating the frequency in the test signal that cancels out the gravitational shift.)
« Last Edit: 28/03/2016 17:25:01 by timey »

#### alancalverd

• Global Moderator
• Neilep Level Member
• Posts: 4729
• Thanked: 156 times
• life is too short to drink instant coffee
##### Re: Why do photons have the same speed regardless of the velocity of their source?
« Reply #106 on: 28/03/2016 23:24:18 »
Alan - The info that Evan quoted stated that the gravitational shift was cancelled out when exactly the correct 'back and forth' motion of the speaker was matched by the correct position of 1 photon being emitted at 1 distance, and 1 photon being emitted at a different distance... (It didn't quite say this, but this 'is' what it meant, because frequency is the result of oscillation)

It didn't say that, because it didn't mean that. Doppler shift derives from velocity, not position.

Quote
I don't understand your fixation with the terminology Doppler shift... :(
The experiment states that a Doppler shift was created to measure the gravitational shift.  What more do you want me to say about it?

Preferably nothing, once you accept the difference between Doppler shift, gravitational shift, and frequency mixing. Which, judging by your next remark, you haven't

Quote
My observation is that 'relative motion' was used in the test signal to measure gravitational shift over a 'fixed' distance.  The relative motion was caused by, what looks very much to me, like a 'time delay'.  The light emitter was being reverberated.

(Edit:  The noise from the speaker will be having no effect on the light whatsoever - it is the noise that drives the speaker, and hence the subsequent oscillations in the speaker cone, upon which the light emitter is mounted, that is creating the frequency in the test signal that cancels out the gravitational shift.)

#### timey

• Neilep Level Member
• Posts: 1309
• Thanked: 9 times
##### Re: Why do photons have the same speed regardless of the velocity of their source?
« Reply #107 on: 28/03/2016 23:40:59 »
Alan... I do know the difference between a Doppler shift, gravitational shift and frequency.  I know the difference between lights frequency, and sounds frequency and how the frequency of both affect wavelength.

However, from everything that I have read about concerning space time and the Lorentz transformations, 'relative motion' should not occur for light within a fixed distance of the gravitational field.

Whatever it is you wish to call it, relative motion was created in the test signal.  This 'relative motion' was reflected in the phenomenon being measured over a fixed distance.

Why?

#### timey

• Neilep Level Member
• Posts: 1309
• Thanked: 9 times
##### Re: Why do photons have the same speed regardless of the velocity of their source?
« Reply #108 on: 31/03/2016 15:03:47 »
...and helicopters were not deployed?

(Perhaps it's a ridiculous question...)

#### timey

• Neilep Level Member
• Posts: 1309
• Thanked: 9 times
##### Re: Why do photons have the same speed regardless of the velocity of their source?
« Reply #109 on: 31/03/2016 16:25:43 »
...and helicopters were not deployed?
(A 'Natural Born Killers' reference, btw.)

Sound is the propagation of a pressure wave through a medium of particles.

Redshift and blueshift is the propagation of a light wave through a medium of gravitational shift.

Maybe it is a ridiculous question, but, I repeat...  In the Pound Rebka, whatever it is you wish to call it, 'relative motion' was created in the test signal.  This 'relative motion' was reflected in the phenomenon being measured over a 'fixed' distance.

Why?

#### alancalverd

• Global Moderator
• Neilep Level Member
• Posts: 4729
• Thanked: 156 times
• life is too short to drink instant coffee
##### Re: Why do photons have the same speed regardless of the velocity of their source?
« Reply #110 on: 03/04/2016 23:27:51 »
Because the "phenomenon measured over a fixed distance" was a frequency shift of the incoming photon due to the gravitational gradient over that distance. Here's the A level explanation (the real experiment involves a tiny bit more sophistication)

Static, "classical" case: 57Fe nucleus emits a photon with frequency f → photon detected by the receiver if and only if the received frequency is exactly f. This is the Mossbauer effect.

Static, relativistic case: Add a gravitational gradient: 57Fe nucleus emits a photon with frequency f → gravitational red (or blue) shift means the receiver sees  f + δf ∴ no signal.

Now add a Doppler shift by moving the receiver.  At some point during the sinusoidal motion  the Doppler shift will be -δf so the receiver will see the incoming photon as having frequency f and you will get a signal out of the receiver.

We know that the Doppler shift is given by v/c where c is the speed of light and v is the instantaneous velocity of the receiver, so we can calculate δf, the gravitational shift.

What makes this a really clever experiment is that you are measuring a tiny change in a really big number, with some remarkably crude equipment (a bass loudspeaker!). Hats off (and indeed a Nobel prize) to Rudolf Mossbauer, massive praise to Pound and Rebka, and everlasting respect to all  bass-playing physicists.

The following users thanked this post: jeffreyH

#### The Naked Scientists Forum

##### Re: Why do photons have the same speed regardless of the velocity of their source?
« Reply #110 on: 03/04/2016 23:27:51 »