EPR Paradox

Quantum mechanics took a giant leap with the principle of uncertainty. This principle was developed by Werner Heisenberg . According to uncertainty principle no one can measure velocity and precise position of an particle simultaneously at any given moment of time. Our very act of measurement of one quantity causes high degree of error in value of other quantity. This means that if not measured, a particle does not have a definite velocity and momentum before we perform an act of measurement. Einstein along with other fundamentalist were not convinced. According to him closing our eyes and not watching the moon doesn’t mean moon is not there. Moon will be part of the reality whether we are looking at it or not. So three scientist Einstein, Podolsky and Rosen (EPR) found out a way to a way to derive a way to measure particle’s both speed and position without actually disturbing the  particle.

In physics we encounter many instances where two particle (of same mass, density)collide with one another and travel at same speed after collision. This happen in accordance to newtons third law of motion. So by measuring position and velocity of one particle we can determine velocity and position of the other particle without actually disturbing the other particle.

This proved that a particle can have definite position and velocity. But EPR experiment did not put an end to this debate . Quantum physicist shot back with Entanglement Principle. At the end EPR had to admit that we cannot measure position and velocity simultaneously and uncertainty in it was valid. But it was Einstein’s frequent arguments against Quantum mechanics which led to its developement


One thought on “EPR Paradox

  1. “This means that if not measured, a particle does not have a definite velocity and momentum before we perform an act of measurement” – I agree that this idea is flawed. If a car is traveling down the road and I do not measure it’s speed, this doesn’t mean that it has no speed at all. But maybe what is meant is that if there is no capability to mesaure it then it has no speed regardless of whether I actually perform the measurment or not. In this case the car analogy does not hold up for even though I in fact did not take a measurement of its speed, I was certainly capable of measuring its speed. So what about the case where there is no capability to measure it. Well that also depends on who is doing the measuring. People in time past were not capable of measuring certain things that we can now. And who’s to say that now we are not capable of measuring things we will be later. It seems to be a claim of omniscience that because we can’t measure something now, therefore we cannot measure it in the future either.

    But then again what if all that’s meant is that is has a speed but that speed is indefinate. What is meant by therm indefinate? If all the term means is that we do not know what the speed is, then I grant that without measuring the speed we will not know what it is and therefore it is indefinite in this sense. However, if what is meant is that it has some variable all-speeds-at-once attribute, then I certainly deny that this is possible for it is inherently irrational. It violates the law of non-contradiction.

    But what if all is meant is that if we can’t observe the velocity, then it has no velocity. I deny this is possible. I also deny it is possible for a thing to have an all-velocities-at-once indeterminate value just because we can’t observe it.

    I also see potential problems with Einstein’s proposed solution. (1) How would you know that there are only two particles that are going to collide? You would have to observe/measure them to know that they were there. (2) Even if you only measured one of them, you still have the same problems in the uncertainty principle. How would you know that in trying to conduct the very experiment, you hadn’t added extra energy, or extracted it in order to set up your controlled experiment. (3) Even if you were sure about only having 2 particles and having them collide under controlled measurable circumstances, how would you know the result you were looking at was the same two (or one) particle and not a different one. In order to know what you were looking at in the results you would have had to watch the particles the entire way through, which is impossible because everytime you observe one, you influence it in the very act.

    I agree with Einstein that particles have definate velocities and momentums even if they are unknowable together. I just disagree about how he tried to prove this conclusion. In metaphysics, essential attributes make a thing what it is. It first needs to be established if a particle’s attributes of velocity and momentum are essential or accidental properties. I would argue they are essential even if the values are zero. In this case, if a particle has no velocity or momentum then it is no longer a particle and is something else, which of course must then be defined.

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