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

Sun Vanishes - How Long Till Orbits Change?

  1. Dec 3, 2009 #1
    I've wanted to know this for 15 years. If every particle in the sun simultaneously tunneled to another galaxy, how long would it take the earth to stop orbiting as if the sun were there? 0 seconds? ~7 minutes? Why? How fast does space-time un-deform?
     
  2. jcsd
  3. Dec 3, 2009 #2

    Matterwave

    User Avatar
    Science Advisor
    Gold Member

    ~8 minutes. The speed of gravity is the same as the speed of light, according to General relativity.
     
  4. Dec 3, 2009 #3
    1 vote for the 'speed of light' column. Would there be any practical way to test this? Or has such a test already happened and I just don't know about it? As I understand it, general relativity said that basically nothing can happen faster than speed of light in vacuum, including the transmission of information, but now we say that entwined particles somehow break this rule. Thanks for the reply!!
     
  5. Dec 3, 2009 #4

    Borek

    User Avatar

    Staff: Mentor

    And you will not know for about 8 minutes.
     
  6. Dec 3, 2009 #5
    *rushes to eBay to sell his Magic: the Gathering collection* Thanks for the post!
     
  7. Dec 3, 2009 #6
    From http://en.wikipedia.org/wiki/Speed_of_gravity[/b] [Broken]

    "Several physicists, including Clifford M. Will and Steve Carlip, have criticized these claims on the grounds that they have allegedly misinterpreted the results of their measurements. Notably, prior to the actual transit, Hideki Asada in a paper to the Astrophysical Journal Letters theorized that the proposed experiment was essentially a roundabout confirmation of the speed of light instead of the speed of gravity. [15] Further, there has been criticism of the means by which these results were presented, in that they were announced at a meeting of the AAS instead of being submitted for peer review. [16] However, Kopeikin and Fomalont continue to vigorously argue their case and the means of presenting their result at the press-conference of AAS that was offered after the peer review of the results of the Jovian experiment had been done by the experts of the AAS scientific organizing committee. Asada's claim was found theoretically unsound and disproved in later publication by Kopeikin and Fomalont [17], which operates with a bi-metric formalism that splits the space-time null cone in two - one for gravity and another one for light. The two null cones overlap in general relativity, which makes tracking the speed-of-gravity effects difficult and requires a special mathematical technique of gravitational retarded potentials, which was worked out by Kopeikin and co-authors [18][19] but was never properly employed by Asada and/or the other critics."

    Suffice it to say, this clearly isn't something a total layman is going to understand this side of a physics degree. *sigh*
     
    Last edited by a moderator: May 4, 2017
  8. Dec 3, 2009 #7

    Matterwave

    User Avatar
    Science Advisor
    Gold Member

    I think the gist of it is, we see a delay in response time, but is that delay due to the finite speed of gravity or the finite speed of light? Both effects must be considered.

    The details are quite complicated however...
     
  9. Dec 3, 2009 #8

    Integral

    User Avatar
    Staff Emeritus
    Science Advisor
    Gold Member

    Re: From http://en.wikipedia.org/wiki/Speed_of_gravity[/b] [Broken]

    This is a claim made a few years back to be a actual measurement of the speed of gravity. It turned out to be in error. The speed of gravity remains unmeasured, it is predicted by theory to be the same as c.
     
    Last edited by a moderator: May 4, 2017
  10. Dec 3, 2009 #9
    I learned a long time ago, when a physics geek says "complicated", that means "hide under the bed and suck your thumb." Thanks for the post ;)
     
  11. Dec 3, 2009 #10
    Re: From http://en.wikipedia.org/wiki/Speed_of_gravity[/b] [Broken]

    Thanks for the post, Integral. I'll put this on my list of questions to ask God, should I get the chance.
     
    Last edited by a moderator: May 4, 2017
  12. Dec 3, 2009 #11

    Fredrik

    User Avatar
    Staff Emeritus
    Science Advisor
    Gold Member

    There are some old threads about this, so you might want to search for them too. It's not correct to just answer this question with "8 minutes", because there's no solution of Einsteins equation that describes spacetime around a star that just vanishes. So the question doesn't make sense as it stands. You can however imagine the sun being pulled away slowly, and in that case, the effect spreads at the speed of light and will therefore be noticeable about 8 minutes after you start.
     
  13. Dec 3, 2009 #12
    It is definitely an intentional part of my question that this is *NOT* a gradual change. Let's say this is a weapon of an advanced, alien civilization. I want to know what happens when the source is just GONE, not moving at a pleasant, manageable <c.

    You could rephrase this as "Aliens threaten to instantly tunnel all of Sagittarius A* to the edges of the universe. How long do human technologists have to respond?"

    Thanks for the post!
     
  14. Dec 3, 2009 #13

    Matterwave

    User Avatar
    Science Advisor
    Gold Member

    There are no known mechanisms by which matter/energy could just be gone. If an advanced civilization annihilated the Sun completely, it would all be converted into energy and this energy would still be deforming space-time.

    If you are talking about tunneling, there is no way the Sun can "tunnel" to somewhere else since it's a macroscopic object, always being "observed" and interacting with other objects in such a way that its wavefunction will not have time to diffuse according to the Schrodinger equation.

    If you are talking about say, the gravity of a particle which may tunnel, then i have no idea. The general theory of relativity has not been brought together with Quantum mechanics. It's actually one of the main points of study at this time.
     
  15. Dec 3, 2009 #14
    Thanks for the post. I want to know, but not so much I'm about to dive into superstrings or M theory or the such. I think I'll focus on trying to understand what "time to diffuse according to the Schrodinger equation" means for now.
     
  16. Dec 3, 2009 #15

    Matterwave

    User Avatar
    Science Advisor
    Gold Member

    Any particle can be described by it's wavefunction which evolves according to the Schrodinger equation. The Schrodinger equation tends to smear out the wave function over time (the wave packet tends to grow flatter and wider) since, in form the Schrodinger equation is very similar to a diffusion equation, unless something is preventing this from occurring, such as wavefunction collapse (or if the particle is stuck in some sort of potential well).
     
  17. Dec 3, 2009 #16

    Fredrik

    User Avatar
    Staff Emeritus
    Science Advisor
    Gold Member

    I didn't change your question to make it easier to answer. I changed it because it didn't make sense.

    Regarding your new question, the answer would depend on how the sun is moved. If it's through a wormhole, we're still dealing with a star that moves away slowly (through the wormhole) so my previous answer still applies, and you would have to add the contribution from the wormhole.
     
  18. Dec 3, 2009 #17

    A.T.

    User Avatar
    Science Advisor
    Gold Member

    Much of physics is based on the assumption of energy conservation, which would be violated by this premise. So basically you are asking:

    "What would the laws of physics predict, if the laws of physics were wrong?"
     
  19. Dec 3, 2009 #18

    Dale

    Staff: Mentor

    Well said.
     
  20. Dec 3, 2009 #19
    The problem with hypothetical but impossible questions like this is that they are contradictory with theory. Literally anything can be derived from a contradiction, so these questions are impossible to answer without modification.

    Edit: I see the contradiction has been stated above :smile:.
     
Know someone interested in this topic? Share this thread via Reddit, Google+, Twitter, or Facebook