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Is the Pioneer Anomaly Really Solved ?

  1. Nov 11, 2012 #1
    What evidence proves that photon emission of an object, - at all sends some of its momentum back to the source, - and thereby cause it to decelerate (or move opposite)?

    Or what is the evidence proving that photon emission at all do have a decelerating influence on the object emitting the photons?

    Are the Earth and the Moon also pushed away from the Sun due to photon emission / reflection? - I guess no, not at all.
  2. jcsd
  3. Nov 11, 2012 #2
    Look up radiation pressure. Also: due to the conservation of momentum anything that emits more light in one direction than the other one will be pushed. There have been simulations that show results compatible with the Pioneer anomaly so most people say that the issue is resolved. We don't need to question an established theory like general relativity if there is no hard evidence against it.
  4. Nov 11, 2012 #3
    I have read about it. It is easy to accept this part.
    It seems to be logical that the pressure is real so long something (matter) is hit by photons.
    But it still seems to me that photons bombarding a piece of matter, - is very different from photons bombarding empty space (as reflecting photons from the Pioneer spacecraft did).

    Which scientific evidence are we now talking about?

    Most people say so much. Science must be based on the scientific method; otherwise it is not science to me.

    To my opinion, - test of relativity is always necessary until all aspect are proven by the scientific method.

    It don’t seem logical to me that "due to the conservation of momentum anything that emits more light in one direction than the other one will be pushed"
    Simply because how can pressure exist so long the bombardment is against empty space?

    • Which scientific evidence is supporting this part?
    • Does any experiment or observation support that?
    • Why do you think relativity should lead to such conclusion?
  5. Nov 11, 2012 #4
    How can it not be logical? If radiation pressure exists, and has been experimentally observed, then by Newton's third law of motion and the conservation of momentum, the source of that radiation must also experience a force in the opposite direction. Do you really need experimental evidence for this? Empty space has nothing to do with it.
  6. Nov 11, 2012 #5

    Vanadium 50

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    Momentum is conserved. The fact that light carries both momentum and energy is both theoretically and experimentally established. Arguing otherwise will get this thread locked very quickly.
  7. Nov 11, 2012 #6
    It seems to be some “missing link here”, that's all.
    Newton’s third law is based on simple mechanic. This question here is not that simple. At least not to me.

    Well, let’s now follow the photon leaving the space probe, let’s say it was emitted towards the Sun, (towards the antenna) - the emission should now instantly push the spacecraft forward, (opposite the Sun) - whereby the space probe must accelerate, not decelerate.

    The next thing that happens is the photon is hitting the antenna, and is changing direction; and then zig zag now towards the space probes motion direction.



    Let's say the reflected photon exert a similar influence, the space probe must now decelerate due to the backwards push towards the new direction, - but since the emission caused acceleration initially, - the net result must cancel out? –and hence zero - or?

    I am not arguing otherwise, but just asking how we can distinguish between what is proven by the scientific method and what is not. The Pioneer Anomaly has for decades been a mystery, now we are ready to close that chapter, - how sure can we be that we not just are closing our eyes?

    I am always willing to accept scientific facts, - But how can I be sure when something not is proven by the scientific method?

    There must be no barriers to freedom of inquiry ... There is no place for dogma in science. The scientist is free, and must be free to ask any question, to doubt any assertion, to seek for any evidence, to correct any errors.
    Robert Oppenheimer.
    Last edited: Nov 11, 2012
  8. Nov 11, 2012 #7


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    It is exactly that simple. The complicated part is calculating the exact effects of the radiation pressure emitted from the spacecraft's different parts.

    Most of the heat producing electronics are behind the main dish, so the radiation emitted from both sides of the spacecraft are unequal, with most of it being directed in the direction the spacecraft is moving.

    We can't. We can't be sure of anything. Ever. However new calculations show that when you include the radiation pressure from the spacecraft, no anomalous acceleration remains. IE the effect can be explained by thermal emission from the spacecraft and doesn't require any new physics.

    The scientific method proves nothing. It is merely a way to find possible solutions to problems. You can never prove anything 100%.
  9. Nov 11, 2012 #8
    I would say it is more complicated to know whether we are on the right track, so long there are no real scientific evidence.

    Right but as I wrote the zig zig path of the photon can be compared to by turns to get slaps at the right and left cheek, - which way will the man finally fall ? To the right or to the left?

    Ahh come on. I feel myself pretty sure that Venus orbit the Sun, not the Earth.

    That’s right, but notice many articles claims this is "the most likely reason".
    I am not so convinced; you can program a software the way you want. A computer only does what it is told to. Imaging the photons would zig zag between the antenna and the main ship forever, - honestly - would that not just forever cancel out the opposite impact influences?
    Which different does it make if the photons escape the trap after short time? – So long they are zig zag towards opposite direction of the space probes, - the result seems to me, - must be about zero.

    I can prove that my thump is to the left on my right hand and opposite on the left hand. This is based on observation and hence based on the scientific method. . But I cannot see what the photons does and not does. nobody can, also not NASA, - That’s the differences.

    Never the less, what i do see at the drawing seems to be a zero result. - But in this case I agree we don't know, we only believe the Pioneer Anomaly maybe is solved, because this is what we are told to believe.

    There must be no barriers to freedom of inquiry ... There is no place for dogma in science. The scientist is free, and must be free to ask any question, to doubt any assertion, to seek for any evidence, to correct any errors.
    Robert Oppenheimer.
  10. Nov 11, 2012 #9


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    There is plenty of evidence. We know how radiation pressure works and can measure it to a very precise value in experiments. Just because we aren't physically there doesn't mean we can't apply it to the Voyager probe. Applying known science to solve problems is exactly what you are supposed to do. In this case we had a problem, re-examined it and applied known physics, and the end result eliminated the problem. This is EXACTLY how almost all problems are solved in life.
    Your diagram is incomplete. Radiation is being emitted in different directions, not just from the dish towards the electronics. Besides, the final direction the photon moves in is what matters, not how many times it is reflected. Those reflected photons will eventually be reflected away from the spacecraft in the direction of motion since they originated on that side of the dish.

    There is no way to prove it absolutely. A sufficiently complicated set of rules could duplicate our measurements but have Venus be the center of the universe or something.

    This has nothing to do with a computer, it only does the math for us. Real people were in charge of finding solutions, and several had been presented prior to a detailed analysis of the radiation pressure.

    They do not zig zag forever. They will either be absorbed or reflected away from the spacecraft. Absorbed photons end up imparting no net acceleration, while reflected ones do.

    No, you cannot prove that with absolute certainty. The fact that you even think you can points out that you don't understand the scientific method.
  11. Nov 12, 2012 #10
    I am not so sure. I have tried to Google exactly which kind of experiments proves that photon bombardment really can accelerate an object. I only found some superficially descriptions of experiments done long ago.

    I would be happy to get some better links to read more about such experiments. - But "plenty of "evidence" ? - Remember everything can be interpreted different, - for example if the devil read the bible it is not sure it would be understood the same was as when we do. ´

    I also notice that plenty of experiments failed to prove the predicted influence. So in its very basic I am not convinced that photons bombardment really can force anything to move. - No doubt that photons can be absorbed and that this will increase the energy (and "pressure") of an object, but this I believe we both agree is something very different.

    I could very easy accept that impact of photon really has the predected influence, simply because this part sound logical. Still I would like to have that confirmed and read which experiemt did really prove that.

    Here is the bone of content...
    I mean the direction from where an impact comes from matter; - Yes this sound acceptable and logical.
    But the direction the photon moves after hitting something - does that really matter?
    What exactly is the evidence for that part?
    I am asking for a specific experiment that proves that idea.
    This part is really very hard to swallow.

    I am happy so long things sound rational and logical, or at least really are proven by experiments or direct observation. I cannot accept hokus pokus science.

    I think we have reached the "bon of content" as I wrote above.
    The data that feeds the computer is off course important, - if that part is on really thin ice, the whole solution is too.


    The method is simple, we could for example replicate the experiment, build 2 new Pioneer probes, let them move towards the same direction, BUT replace the heat emitter so that heat NOT is reflected.
    And parallel with that also launch 2 copy of the old Pioneer probes, on the same time/ path...
    Now 2 probes should decelerate and the 2 new models not.
    Is that what would happen?
    In this case experiments and the scientific method have taken over.
    Such would to me be very acceptable, logic and rationel science. Science approved by experiments, and hence by the scientific method.

    We have seen too many times that our conclusions and expectation were wrong, - such is not science.
  12. Nov 12, 2012 #11


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    I don't see why you need modern experiments if the original ones prove this effect. For example here is the original device used to measure it. http://en.wikipedia.org/wiki/Nichols_radiometer
    Here's the link to the actual journal the results were published in: http://www.scribd.com/doc/76312661/...Annalen-Der-Physik-Pyotr-Lebedev-1901-English
    You could probably make one at home.


    Your personal interpretation is irrelevant. The fact is that radiation pressure is used extensively in astronomy and astrophysics. For example I just read today in Sky and Telescope magazine about how the emission of radiation influences asteroid rotation rates and can cause them to spin up fast enough for a piece of it to actually break off. Page 32, December 2012 issue. Here's a link to the YORP effect as it's named: http://en.wikipedia.org/wiki/Yarkovsky–O'Keefe–Radzievskii–Paddack_effect
    Also, here's an actual research paper that uses it: http://arxiv.org/abs/1210.2219
    Heck, here's a link where you can see all kinds of research papers involving it: http://arxiv.org/find/all/1/all:+yorp/0/1/0/all/0/1

    Here's info on a solar sail, which has been used in real life to move an actual spacecraft. http://en.wikipedia.org/wiki/Solar_sail

    Here's the explanation of radiation pressure. Note that reflected radiation imparts twice the momentum. http://en.wikipedia.org/wiki/Radiation_pressure

    Newtons laws of motion, conservation of momentum, and plenty of others. If a photon is reflected or emitted in a direction it MUST impart a force in the opposite direction due to conservation of momentum. The Nichols Radiometer is a perfect example of this.

    This is nonsense. It is a complete waste of time and money to build new spacecraft and launch them into an escape orbit just to see if radiation pressure is really the culprit.

    The REAL issue I see here is your unwillingness to trust that scientists know what they are talking about because it doesn't sound logical to you. Also, consider that the internet hasn't been around for the most of scientific history, so many of the initial experiments that established basic laws, and subsequent ones that further refined them, simply aren't available online in a word for word copy unless you know where to look. Most experiments were published in journals that may or may not have been copied to an online format. In many cases they have, as I've seen more than a few links to an article in Annalen der Physik, a popular scientific journal that even Einstein used. Even today many experiments are published in for-profit journals and cannot be found online without paying.
    Last edited: Nov 12, 2012
  13. Nov 12, 2012 #12
    Thank's for all the links.

    I have not fully understood that experiments, a lof of speciel technical terms are used, and english is not my first language. I need more time.
    Can you short explian why you think the Nichols Radiometer proves that reflected radiation imparts twice the momentum.

    How is that possible, how can the photon transfer kinetic energy to the object it hit, and at the same time not lose energy (or momentum) ?
  14. Nov 12, 2012 #13


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    If the object gains kinetic energy, the photon will lose some (and get red-shifted). This happens if the spacecraft moves in the same direction as the photon in your reference frame.
  15. Nov 13, 2012 #14


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    I'm not sure how to answer that. Because we measure the amount of light and how much is absorbed and reflected, and then how far the radiometer moves? I doubt that this single experiment is the sole example of this effect.
  16. Nov 14, 2012 #15
    I think you are right accorindg to the photon radiation push
    I must say after reading it seems to be very logical and not hokus pokus as science sometimes also can be.

    I notice this

    18%,is to my opinion too much.

    The speed of the Pioneer Proves was about 12000 m/s
    Do you know how that is measured?
    I know it is based on blueshifted signals, but I think about time / distance factors.

    Are there an easy way, that we can say it is based on the Probe time / distance reference frame (second by second)?

    How is the calculation actually done?
    I expect a couple of equation are used.
    What about Shapiro delay
  17. Nov 14, 2012 #16


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    Given the complex set of circumstances, the unknown physical state of the spacecraft, the still mostly unknown conditions at the edges of the solar system, and plenty of other concerns I'd say 18% uncertainty is pretty good.
  18. Nov 14, 2012 #17


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    18% uncertainty on what, and 18% relative to what?

    If the uncertainty on the effect of radiation emission is 18%, and the deviation between prediction and measured "anomaly" is within 20%, there is no anomaly left. It would be nice to get better predictions, but that is optional.
    If there is an 18%-deviation between prediction and measured anomaly and the uncertainty on the prediction is below 5%, that would be a serious issue.

    I hope you do not mean physics here.

    Doppler shift of radio signals. They are redshifted, as pioneer is flying away from us.
    That cannot be measured second by second, as the signal itself needs hours to reach the probe. You have to consider the velocity of earth (and its change in the orbit), the rotation of earth and probably several other effects. Gravitational time dilation cancels as the signal goes both ways.
    Last edited: Nov 14, 2012
  19. Nov 14, 2012 #18
    Right I wrote "measure", but I meant, how is the distance calculated?
  20. Nov 14, 2012 #19


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    The distance can be evaluated via timing - not very precise, but probably good enough as the probes are far away from any massive object and their position is not so crucial.
  21. Nov 15, 2012 #20
    It must be important that we know which distance we expect the space probes to be
    Also a way of calculating this ?
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