Thread: A Question on Relativity (Paradox)

Not sure if similar questions like this has been posted, but here it goes.

Say 2 particles A and B.

Particle A is stationary in this inertial reference frame.
Particle B is moving with constant velocity v=0.8c

Both is a similar isotope of the same radioactive element.(hence, supposedly same half-life)

Q1: Which will decay faster in this reference frame?
In theory, it's A(stationary), B will decay slower due to time dilation.

However, if we change our perspective and take a different reference frame, B is stationary in this refernce frame. Hence, A is moving in the opposite direction with v=0.8c relative to B.

Q2: Which will decay faster this time?

Q1: wrong. They both decay at the same time rate. Think of it like this:
P1 and P2 pass though a street (time) the speed of P2 though time decreases while increasing the speed though space; the speed of decay is not effected.

Q2: regard Q1.

When dealing with relativity, doesn't the manner in which you view these occurances have a large impact on what happens at what time? If both particles are visable, the light from the closer object will extinquish first, thus making the closer object decay first from your point of reference.

I dun think it is the distance that matters because i regard them as relatively same distance from me. Even if A(stationary) is very far away from me(say, its half-life is measured by another observer with same reference frame in Germany), i will obtain the same "observation": A will decay in a lesser time.


Hmm.. regarding the rate of decay. it depends on what is ur reference frame. If ur reference frame is same as A(A is stationary to u), A will decay first. Because time has slowed down for B, time passed more slowly for B, in your point of view. If u had an identical twin moving at the speed of B, he would be younger than u.

However, if u take reference frame of B, A is moving, so B will decay first. Same rate of decay per second, but this "second" here is the perspective of the observer's reference frame.

So, the conclusion is, depending of your postion(reference frame), both will register different outcome.

i post a similar question in this forum: http://physicsforums.com/showthread.php?t=194666 too, and recived quite a number of intuitive feedbacks.

Those who are interested can read up there too. lol

I think your example is not really good. You cann't make a statement about something governd by the laws of quntum mechanics for a single atom. Schötinger has treated that in some interesting thought experiment by killing his cat

And if the two observers would compare their measurements (assuming they actually can measure what they intend to) they'll end up with the same values as the reference fram for both the clocks and the particles are the same thus change in time dilation is the same for the measurement equippment and the object to be measured.

Particle A would decay faster to an outside observor provided that we are allowed to observe this externally from this system. Could you clarify a bit so I can get to grips with it a bit more .

Hmm.. actualli there is not necessary to define an outside the system ref frame. In special relativity, there is no previlaged "rest frame" or so called zero speed frame. The objects speed is whatever speed it is, relative to our ref frame. When i state the Germany example, im assuming that the stationay particle A is the same frame as the Earth(we can assume that the Earth as a giant rest frame, though it actually isn).

Assuming that B's ref frame is actually the same frame of ref as the Earth(meaning, to an "outside observer" Bis the one that is stationary), an observer with the same ref frame as A(moving at the same speed in the same direction as A) will also observe the same result.

Seems that result that, "stationary object decay faster", is true for which ever ref frame u take.

yes both at the same velocity would see the same result. No faster decay then. I though you could have a 3rd observor as I thought one of the 2 were stationary.