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

Do entangled particles decay simultaneously?

  1. Oct 28, 2014 #1
    I apologise in advance for my rather minimal knowledge of physics. Please assume that anything I write below is just my current understanding, and may very well be incorrect...
    1. Elementary particles decay into other elementary particles.
    2. When a a subatomic particle decays into a pair of other particles, entanglement occurs.
    3. According to special relativity, a particle accelerated to near light-speed will experience time much more slowly than a particle that is not accelerated.
    Let's say I have a pair of entangled particles that were generated at the same time by the decay of another particle. Let's call them X and Y. Will X and Y decay at the same time?

    If so, what then happens if I accelerate Y to near light speed?

    From the point of view of a stationary observer, do X and Y...

    (a) Decay at the same time (relative to the stationary observer)?

    (b) Last for the same length of time relative to their own inertial frame, so that Y decays after X?

    If (b) is true, then does that allow us to predict exactly when Y will decay?

    Are there suitable particles that would allow this to be done experimentally?
  2. jcsd
  3. Oct 28, 2014 #2


    Staff: Mentor

    When decay occurs can only be predicted probabilistically.

    The so called proper time (the time a conceptual clock moving with the particle) is what theory predicts and is frame independent. For particles near the speed of light the time measured will be much longer. This, as explained by SR, is due to space time geometry analogous to rotating a rod to fit through a door. In fact the analogy is quite close, requiring so called hyperbolic rotations instead of the usual ones.

  4. Oct 28, 2014 #3

    Vanadium 50

    User Avatar
    Staff Emeritus
    Science Advisor
    Education Advisor
    2017 Award

    No. This experiment has been done hundreds of millions of time in Palo Alto, California and Tskuba, Japan.
  5. Oct 28, 2014 #4
    Can you link to details of the experiments, or perhaps just what I would search for in Google to find some details? Thanks
  6. Oct 28, 2014 #5

    Simon Bridge

    User Avatar
    Science Advisor
    Homework Helper

    Just to clarify:
    ... This is not correct.
    According to special relativity, all observers experience time at the same rate, but disagree about each other's time-rates.
    In the twin's paradox, the accelerated twin does not "feel time slow down"; but, instead, would argue that the other twin spent some period aging quite rapidly.
  7. Oct 29, 2014 #6


    User Avatar
    Science Advisor

    Just by saying that "two particles are entangled" does not allow you to make any predictions. You must specify how are they entangled, i.e. you must specify their joint wave function. Depending on this wave function, they may or may not decay at the same time. Furthermore, it the wave function is of a kind that does imply a simultaneous decay, different wave functions of that kind will imply simultaneous decays in different Lorentz frames.

    That being said, it is important to stress that most wave functions that you can write down do not imply simultaneous decay at all. From the experimental point of view, I think that a state (wave function) corresponding to a simultaneous decay has never been prepared in a laboratory.
  8. Oct 29, 2014 #7

    Vanadium 50

    User Avatar
    Staff Emeritus
    Science Advisor
    Education Advisor
    2017 Award

    Look up the BaBar and Belle experiments.
  9. Mar 30, 2016 #8
    It may be worth noting that point b) from the OP is almost correct. Namely, while it is not at all guaranteed for a specific pair of particles, it is true on average. That is, the half-life of the sped up particle is affected by time dilation as you would expect. Of course, entanglement plays absolutely no role in this.
    (Bugger, I see the date of this thread now and I wonder where did i find the link to it at all? Oops, sorry guys.)
Share this great discussion with others via Reddit, Google+, Twitter, or Facebook

Have something to add?
Draft saved Draft deleted