🚀 go-pugleaf

Max Keon skrev:
> "Paul B. Andersen" <paul.b.andersen@guesswhatuia.no> wrote in message
> news:47B5E7DE.8080307@guesswhatuia.no...
>> Max Keon wrote:
>>> Paul B. Andersen wrote:
>>>> Max Keon wrote:
> 
>>>>> If radioactive iron is chosen as the frequency generator in an
>>>>> atomic clock, a GPS radius clock will run _slower_ than the
>>>>> surface radius clock (all fixed with the ECI frame), by 4.55e-5
>>>>> seconds per sidereal day. Not faster. The Pound and Rebka
>>>>> experiment proves that gamma rays are generated in a vastly
>>>>> different environment to that of lesser frequency rays.
>>>> How did you arrive at this remarkable conclusion?
>>>> It is wrong.
>>> Once again, this is the blurb given in "Basic Physics 2, by
>>> S.L.Martin and A.K.Connor", (1960+ vintage), briefly describing
>>> the purpose of the Pound and Rebka experiment.
>>>
>>> -"In 1958 an effect was discovered by Mossbauer, working in U.S.A
>>> -and known as the Mossbauer effect, which enabled very tiny
>>> -frequency differences to be detected and measured. In 1960, using
>>> -the Mossbauer effect, Pound and Rebka succeeded in measuring the
>>> -extremely small change (only about 1 part in 4e+14) of frequency
>>> -of the y-rays emitted by a sample of radioactive iron when it
>>> -was moved from the bottom of the tower to the top of a tower 74
>>> -feet high. The observed frequency change agreed with the
>>> -relativity prediction within 5%."
>>>
>>> Notice that this information was gathered around the time when
>>> the experiment was conducted. The authors would have had very
>>> detailed knowledge of a recently conducted experiment, surely?
>>> It's hardly likely that their description is flawed.
>>>
>>> According to the description given, the emitted y ray frequency
>>> reduced _as the radioactive iron sample was raised to the tower
>>> top_. That is NOT how a normal Caesium driven atomic clock
>>> behaves.
> 
>> According to which description?
>> Certainly not the quoted one.
> 
>>> But perhaps I've just misinterpreted the description.
> 
>> You certainly have.
>> Do you think the Pound & Rebka experiment would be
>> considered to be a confirmation of GR if it had
>> measured the opposite of what GR predicts? :-)
> 
> GR predicts that clock oscillator frequencies are slower in a
> gravity well, while the frequency of an inward traveling photon
> increases.
> 
> This was the purpose of the Pound and Rebka experiment
> according to Brittanica;
> -By Einstein's theory of general relativity a photon produced
> -near the Earth's surface should be higher in frequency by 1.09
> -parts in 1016 for each metre above sea level. In 1960 the U.S.
> -physicists Robert V. Pound and Glen A. Rebka measured the
> -difference between the frequencies of photons produced at
> -different elevations and found that it agreed very closely
> -with what was predicted.
> 
> Pound and Rebka were not out to prove that an atomic clock runs
> slower in a gravity well at all, they were out to prove that a
> photon frequency decreases and wavelength increases as it travels
> upward from a gravity well.

What you don't seem to understand is that the (loosely expressed)
statement "atomic clock runs slower in a gravity well" and the
(loosely expressed) statement "a photon frequency decreases as
  it travels upward from a gravity well" express the same phenomenon.
See below.

> 
>> You can read about the P&R experiment here:
>> http://luth2.obspm.fr/IHP06/lectures/mester-vinet/IHP-2GravRedshift.pdf
>> http://focus.aps.org/story/v16/st1
> 
>>> It really
>>> doesn't matter though, the theory of gravitationally redshifted
>>> light is still wrong.
>>>
>>>> f_h/f_o = (1-(GM/r)/c^2)/(1-(GM/R)/c^2)~= 1-(GM/r)/c^2 + (GM/R)/c^2
>>> Which is .9999999999999919 tower top seconds per 1 second at
>>> the tower base.
> 
>> No, you have got it backwards again.
>> If you insert the relevant numbers in the equation above,
>> (or in the equation below, f_h/f_o ~= 1 + gh/c^2)
>> you get:
>> f_h/f_o = 1 + 2.46E-15
>>
>> That is, the frequency on the top is _higher_ than
>> the frequency on the bottom.
> 
> I know what the clock frequencies will be at the tower base and
> tower top, but what will be the frequency of a photon that has
> traveled from the tower base to the top? According to GR, it's
> going to be _lower_ at the top than it was at the bottom.

Please read the following carefully.
We have a tower.
If em-radiation is emitted from one end of the tower, and received at
the other end, all frequencies must change by the exactly the same factor.
That means that if the em-radiation is gamma, the frequency shift
delta_f/f must be the same as when the em-radiation is RF.
If the em-radiation is a series of pulses (or flashes),
the repetition frequency of these flashes must also change by
the same delta_f/f as above.
Now, imagine that we have a clock at each end of the tower,
emitting one flash per second (let the clocks be Cs clocks,
emitting one flash per SI-second).
If the em-radiation going up is shifted to lower frequencies,
then the observer on the top will count fewer flashes from
clock at the bottom, than from his own clock. While he
is counting N pulses from his own clock, he will have counted
only N-n pulses from the bottom clock. This process is cumulative,
so he will see that the bottom clock is lagging more and more
behind his own clock. The bottom clock is running slower than
the top clock.

The (loosely expressed)statement "clocks runs slower in a gravity well"
and the (loosely expressed) statement "a photon frequency decreases as
it travels upward from a gravity well" express the same phenomenon.

> 
>>> That oscillator is running faster deeper into
>>> Earth's gravity well. A Caesium atomic clock oscillator runs
>>> slower. Regardless of whether that is so or not, none of that
>>> has anything to do with redshifted wavelengths on the climb from
>>> a gravity well, as you will see.
>>>
>>>> where:
>>>>   f_h = frequency of gamma photon at the top of the tower
>>>>   f_o = frequency of gamma photon at the bottom of the tower
>>>>   r = the distance centre of the Earth - top of tower
>>>>   R = radius of the Earth (at the bottom of the tower)
>>>>
>>>>  r = R + h, h = height of tower
>>>>  f_h/f_o ~= (1 + ((GM/R)/c^2)(1 - R/(R+h))
>>>>  When h/R << 1 :
>>>>  R/(R+h) ~= (1-h/R)
>>>>
>>>>  f_h/f_o ~= 1 + ((GM/R)/c^2)(h/R)
>>>>  g = GM/R^2
>>>>
>>>>  f_h/f_o ~= 1 + gh/c^2
>>>>
>>>>  Which is in accordance with the Pound & Rebka experiment.
>>>
>>> Here's another problem for you, in your reply to Henry Wilson on
>>> this thread. The experiment you have described in this excerpt
>>> from that post is seriously flawed.
>>>
>>> -But other experiments are made.
>>> -In gravity probe A, a hydrogen maser was used as a clock.
>>> -It transmitted a continuous wave with frequency ca. 1.42 GHz.
>>> -This frequency can easily be, and was, directly measured
>>> -from the ground. Every cycle was received.
>>> -(The received frequency was compared to the frequency of
>>> -  a signal reflected off the probe, to compensate for
>>> -  Doppler effect. The gravitational shift was thus measured.)
>>> -The rocket with the maser was launched straight up, and was
>>> -inertial for most of the journey. It reached an altitude of 10000km.
>>> -The relative gravitational frequency shift of the EM-radiation from
>>> -that altitude was ca. 4.2E-10.
> 
>> You can read about it here:
>> http://luth2.obspm.fr/IHP06/lectures/mester-vinet/IHP-2GravRedshift.pdf
> 
>>> The assumption prior to conducting the experiment was that the
>>> wavelengths from the ground source would extend enroute to the
>>> onboard reflector carried on the rocket when the altitude
>>> ceiling of 10000km was reached, and would then shorten back to
>>> their original lengths on return to the point of origin.
>>>
>>> The next assumption was that the hydrogen maser clock was
>>> running faster at the ceiling altitude, according to GM/r/c^2,
>>> which has been well confirmed.
>>>
>>> Assumption (3) was that the wavelengths in the signal from the
>>> maser clock would also shorten in the same proportions as the
>>> return signal from the onboard reflector.
>>>
>>> So, because the frequency in the reflected transmission fell
>>> short of that from the maser clock, one could only conclude that
>>> the transmission from the ground source to the reflector had been
>>> redshifted. But that is not the case at all.
>>>
>>> If the frequency of the round trip signal was constant throughout
>>> the journey, and if the frequency from the maser clock was
>>> constant on the journey to the ground based receiver, exactly the
>>> same result would emerge. The maser clock rate is faster by
>>> 4.2e-10 seconds than the ground clock second. That's all the
>>> experiment is demonstrating, regardless of how the clock rates
>>> are compared.
>>>
>>> Can you not see that?
> 
>> Sure.
>> All what was actually measured was that the frequency received
>> from the probe maser was blue-shifted by the factor (1+4.2e-10)
>> compared to the ground maser, which is the same as saying that
>> the maser in the probe was fast by the factor (1+4.2e-10) compared
>> to the ground maser.
>>
>> Which is in accordance with the predictions of GR.
> 
> What you have described is in accordance with GR's prediction
> for clock rates. It would be an elaborate experiment indeed if
> that's all it was set up to prove.

Yes. But read my statement again.
What was actually measured was that the frequency received
from the probe maser was blue-shifted by the factor (1+4.2e-10)
compared to the ground maser, which is the same as saying that
the maser in the probe was fast by the factor (1+4.2e-10) compared
to the ground maser.

That the frequency of the radiation increases when going down,
means that the high clock runs faster than the low clock.

You seem to think it is the other way around.

> 
> The Pound and Rebka experiment is very similar to the gravity
> probe A experiment, in that a photon emitted from the radioactive
> iron sample at the tower base is assumed to decrease in frequency
> on the climb to the tower top. Confirmation of that being the
> case appears to stem from the fact that resonant absorption of
> the gamma ray emitted from what was initially the tower base
> material does not occur until that material has been raised to
> the same altitude as the receiver. That's the only time when the
> emitted frequency matches the absorption frequency. So prior to
> that event, the gamma ray frequency emerging from the tower base
> material was either faster or slower. As with gravity probe A,
> the assumption is that it was running faster. But atomic clocks
> soundly reject that assumption.

You seem to have grossly misunderstood how the P&R experiment
was performed.
Gamma rays were emitted from the bottom of the tower,
and received at the top. The received frequency was measured,
and found to be red shifted in accordance with the prediction
of GR. As explained above, this also confirms the prediction
of GR that (loosely) "clocks at a higher gravitational potential
run faster when ."
(The experiment was also run the other way, with the emitter
at the top, and the receiver at the bottom.)

What you are referring to above when saying "That's the only
time when the emitted frequency matches the absorption frequency."
is _how_ the frequency of the gamma rays was measured.
The Mossbauer effect is basically the phenomenon that the spectral
line of gamma from a crystal is very narrow because the whole
crystal, and not only one atom, absorbs the recoil from the gamma.
That means that the crystal can only absorb the gamma ray if
the frequency is exactly the same as the one emitted. So if both
the the emitting crystal at the bottom of the tower, and the receiving
crystal at the top were stationary, nothing would be detected because
the frequency wouldn't match.
That's why the emitter crystal was mounted on a loudspeaker membrane
which was driven at a low frequency.
What was actually measured, was the speed of the crystal when
the gamma-rays were absorbed at the top of the tower.
The speed was then exactly right so that the Doppler shift
cancelled the gravitational red shift. When the speed is known,
the Doppler shift can be calculated.



> Is there is any evidence at all to indicate that the frequency
> emitted from the radioactive iron sample at the tower base is
> actually higher than that emitted when it's moved to the tower
> top? If there is, then gamma rays are indeed generated in a
> strange environment.

I hope you by now have cleared up this weird misconception of yours.

>> What else did you think the experiment was supposed to show?
> 
> I was under the impression that the experiment was geared to
> confirm Einstein's prediction that a photon's frequency slows
> on the climb from a gravity well. But it has provided not one
> shred of evidence to support that assumption. Apparently, no
> experiment has.

Now you know better.
Or don't you? :-)

-- 
Paul

http://home.c2i.net/pb_andersen/