# Do entangled particles decay simultaneously?

## Main Question or Discussion Point

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?

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bhobba
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.

Thanks
Bill

Staff Emeritus
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?
No. This experiment has been done hundreds of millions of time in Palo Alto, California and Tskuba, Japan.

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

Simon Bridge
Homework Helper
Just to clarify:
According to special relativity, a particle accelerated to near light-speed will experience time much more slowly than a particle that is not accelerated.
... 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.

Demystifier
2018 Award
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.