Dismiss Notice
Join Physics Forums Today!
The friendliest, high quality science and math community on the planet! Everyone who loves science is here!

General Relativity look at backwards.

  1. Dec 3, 2009 #1
    I have two questions. first, in Einstein's theory of General Relativity the proof was said to come during a solar eclipse. The deflection of light from distance stars as it passed by the sun. How can the proof back in 1919, reconfirmed in early the early 1920s-ish, be confirmed when the photo's where done through the earth's atmosphere? The deflection was so minor it seems that one could not realistically delineate between the effects of the atmosphere and the deflection caused by the sun. which brings me to my second question.

    From General Relativity Einstein tried, in vain, to come up with a theory that unified everything. Why are we looking at all this from the top down? (I admit I am not a physicist and need a calculator to figure out the right tip at a restaurant so my terms my not be spot on.) Why not start from nuetrons, protons and quarks instead of Spacetime, light and what have you?

    It seems that Einstein and everyone else have been tying to explain quantum mechanics, and such, the wrong way around. Shouldn't the starting place be quantum mechanics and then to Special and General Relativity? Trying to figure Special and General Relativity without knowing all the underlying physics is like trying to figure how a computer works using only the keyboard as the point of reference. for the past 50 or 60 years the quantum mechanic theories are "Spaghetti Theory." They get all messed up unless you allow for 5 strings not 1 or if you have a constant this or constant that. The physics of Quantum Mechanics is still "By Chance." Things do not always work the same way in QM.

    Maybe David Hume was right. Back in the 1600s, Hume postulated that everything that happens is by chance. Gravity was chance, the sun rising was chance.... The odds of the Gravity acting differently one minute and different the next where a Gazzlion to 1 yet it was just chance. I think quantum mechanics has proved him right so far. Unless, is it possible to work quantum mechanics, and it's underlying physics, before the theory of General Relativity

  2. jcsd
  3. Dec 3, 2009 #2


    User Avatar
    Science Advisor
    Gold Member

    I will try to deal with your points one by one:

    1) Light bending (any amount) wasn't first theorized by Einstein. Cavendish theorized the bending of light around a massive object like the Sun as early as 1784 (he assumed that light had some mass, and applied Newtonian mechanics). The reason General Relativity wins is that the effect of light bending as predicted by General relativity is twice that predicted earlier, and is the amount that was observed. The confirmation in 1919 by Eddington is sometimes questioned - people have questioned the accuracy of his measurements; however, there have been many measurements of this since then, and they all confirm the validity of General Relativity.

    The effects of the atmosphere are, in general, to "fuzzy up" an image. There's no reason to suspect that the atmosphere would preferentially deflect a star system's light in the same direction and amount that General Relativity predicted.

    2) In Science, we tackle phenomena as they occur. Newton didn't even know about the nature of atoms when he wrote his Principia, and so he only formulated a theory of macroscopic motion. It would be illogical to expect us to build theories only from the smallest of phenomenon up.

    We certainly are exploring the smallest of scales in great detail at the moment (string theory, QFT, QED, QM, etc all deal with the small scale), but I don't think it would be prudent for us to ask everyone to stop and only consider the small scale until we have mastered it. We may never master the small scale (hopefully one day we will), so we may have to wait forever to start "building up", as you say.

    Special and General Relativity explain phenomenon to a very high precision of accuracy; they are useful in everyday life! (GPS uses them to synchonize clocks, for example). We would be missing a lot of technological development if we just put everything macroscopic on hold while we tried to master the tiny scales.

    3) QM is "chance" not in the everyday sense of the macroscopic. Very much, QM just says, before you measure a particle to be at point A, it could be at point A or anywhere around A. This is not to say that QM thinks that the laws of physics could, by chance, vanish one day. If QM said that, then it would no longer be within the realm of physics.
  4. Dec 4, 2009 #3
    Thank You for the response. I didn't know that the atmosphere had little effect in this observation and I am guessing the Hubble Telescope can make a more accurate observation. I always thought observations in QM could have vastly different results from one observation to another observation.

    Also, I didn't mean to infer that we put anything on hold, just to look at the "Tiny Scale" from a different perspective every now and then. I think, and I might be wrong on this, Special and General relativity fit nicely with the way we [thought and think] things should be instead of how things really are. Sort of like Ptolemy working out the orbits of the stars and planets around the earth. The Ptolemaic system worked pretty well before the Heliocentric was finally allowed to be put forth.

    Thanks again.

  5. Dec 4, 2009 #4


    User Avatar
    Homework Helper

    In most cases, the atmosphere is by far--that is, by many orders of magnitude--the most significant source of error. An effect called http://en.wikipedia.org/wiki/Astronomical_seeing" [Broken], the same effect that makes stars twinkle, usually prevents features smaller than an arcsecond to be unresolvable because atmospheric effects make the image shake around so much. Seeing is THE reason why most ground-based telescopes can't produce images that are orders of magnitude more detailed. (Some telescopes have adaptive optics, which consists of shooting a laser into a sky to measure atmospheric effects in real time. Those telescopes have amazing resolution.)

    However, even though images shake around so much due to seeing, a long-exposure photograph shows very clearly where the "center" of the star is. I'd think that pretty much makes seeing a minor issue compared with the practical difficulty of measuring the eclipse photos accurately to determine radial displacement.
    Last edited by a moderator: May 4, 2017
  6. Dec 4, 2009 #5


    User Avatar
    Science Advisor
    Gold Member

    I may be mistaken, but i think the deflection they wanted to see was somewhere around 3-6 arcseconds which would be big enough to rule out atmospheric tampering.

    Anyways, we do use QM for big things sometimes. For example, blackbody radiation is understood as a quantum effect (quantization of light), and we use this to study stars and other astronomical objects.

    We just don't have a (widely accepted) Quantum theory of gravity at this time...it's currently being worked on.
Share this great discussion with others via Reddit, Google+, Twitter, or Facebook