Under Newtonian physics, it is predicted that Mercury’s
orbit would precess slowly around the Sun as a result of the presence of other
planets, which should influence Mercury’s orbit. This is called the “Precession
of the Perihelion”. Initial observations showed that Mercury’s orbit did indeed
precess as the prediction suggested, but the observations could not account for
all of it. Einstein was able to assess this problem and concluded that the
inconsistency came as a result of Newton’s law of gravity assuming that time is
absolute and space is flat. In realizing that general relativity equations
account for spacetime being more curved in the part of Mercury’s orbit that is
closest to the sun, Einstein solved this issue in 1915. Einstein’s work with
general relativity allowed him to develop a predicted model of Mercury’s orbit that
was equivalent to it’s observed output.
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| The perihelion of Mercury advances 2 degrees per century. |
I found this test to be interesting because it was not only
one of the earliest tests that general relativity passed, but it also allowed
general relativity to gain more traction in the scientific community. Furthermore,
while Mercury’s orbit was up for debate, the orbits of other planets were not
as controversial because they are farther from the sun and experience a smaller
shift and Newton’s equations can account for it.
Sources:
Mastering Astronomy p. 433
http://physics.ucr.edu/~wudka/Physics7/Notes_www/node98.html
http://hyperphysics.phy-astr.gsu.edu/hbase/relativ/grel.html
http://www.astro.cornell.edu/academics/courses/astro201/images/merc_adv.gif
Hey Brendan, I think you found a really interesting topic to talk about. I think it is really fascinating to see how the mass and gravitational pull of the other planets affects Mercury's orbit as it travels around the sun. It is truly incredible that Einstein was able to use general relativity to explain the inconsistencies in the original findings. My only question is how did Einstein's knowledge about general relativity lead him to this discovery? I'd love to hear more about how exactly Mercury's changing orbit is related to the concept of relativity. Again, really interesting post!
ReplyDeleteAndrew, I share a similar interest in your question regarding Brendan's post. I also find it intriguing that Einstein was able to solve the discrepancy between previous predictions and observations, but I would like to know how Einstein decided to use general relativity to solve this inconsistency. At first, I did not understand what this precession meant, but the photo really helps to explain this motion and I think you have found a great test of general relativity.
ReplyDeleteI think this is a great example of how a more parsimonious theory is not always preferred. In many senses, Newtonian physics is simpler, but if it is unable to explain the data, or makes predictions that don't match what we observe, and another more complicated theory can explain all the phenomenon, then in many situations, the more complicated explanation is to be preferred or is more likely to be correct. I do wonder though how Newtonian mechanics would have to have been modified to more accurately predict what we observe. I assume the modifications would have been ad hoc, but if they weren't maybe its not as bad of an explanation.
ReplyDeleteThis is an extremely interesting topic. I especially enjoy how it is tied so closely to what we have been learning in class. I can picture Professor Bell sending marbles into orbit in his in class demonstration when I look at the diagram you posted. One question I have about this is whether or not we are able to accurately predict Mercury's orbit into the future. If we are able to do this, I feel this will be beneficial for our understanding of spacetime and perhaps give us a sort of map of the curvature of that area of our solar system.
ReplyDelete