Many Worlds Interpretation of SR

Bruninho

Special Relativity predicts that moving clocks run slow, mass and length are variable and simultaneity is relative. These are 'real' phenomena and leads me to think that the reality of one observer (the passing of time, all physical properties and space-time events) can be regarded as 'his world'. Should this observer change to a different inertial frame he has then entered a new 'world' where physical properties will be seen to change. Are there not then an infinite number of potential realities or worlds? Is reality relative?

misogynisticfeminist

I think that different reference frames doesn't necessarily equate to a different reality altogether. The negation of the concept of simultaneity doesn't necessarily mean that there exists many different realities, the events whic happen doesn't happen simultaneously because the signal reaches different observers at different times.

But the thing is that, the event has already taken place just that it is being percieved at different times. The only physical property which I can think which is changing at different RFs is mass. That is a valid question, how would interactions change due to increased mass? Maybe someone can fill me in on this one.

But other things such as charge or spin doesn't change in any RF. But the most important thing is that physical laws remain the same in any RF. Also, I don't think that anyone's come up with a many-worlds theory for SR. QM, definitely. I don't think SR particularly accomodate a many-worlds theory.

Bruninho

"The negation of the concept of simultaneity doesn't necessarily mean that there exists many different realities, the events whic happen doesn't happen simultaneously because the signal reaches different observers at different times.

But the thing is that, the event has already taken place just that it is being percieved at different times."

I'm not sure about this. My understanding of relative simultaneity is that it 'really' means events occur at different times and not only that they are percieved at different times. Couple this with variable mass, velocity and length and a particular observer must view his world as being quite distinct from that of other inertial frames. That's not to say he can't understand and indeed predict events in other frames but his world view would certainly have a different past and predicted future - not in the outcome of events but in their sequence and timing. But does this constitute a reality or other world?

Perhaps it depends on how you define reality but the reason I'm asking is that it seems to me an intuitive way to picture the very counter-intuitive and very real effects of special relativity. Take the twins paradox for example. In the out leg both see the other age more slowly and this is not a trick. Infact it is very real for both. By taking the view that each twin is in a world of their own (which they can ofcourse return from) so to speak it suddenly seems quite acceptable.

anti_crank

For this idea, you will need the proviso that one can freely change worlds (by accelerating). But I do not think it necessary to reach this far. If event A caused event B, all observers agree on it. So if you define reality as a framework of causality, all observers really do experience the same reality.
In fact, the similar argument can be used for Newtonian mechanics, which does not define absolute motion. So if I see you as moving and you see me as moving, do we need a many-world semantics for that? Intuitively we would say no, and that is because our minds are accustomed to everyday relative motion and encompass it wihin a single reality. I submit the proposal that the relativity of SR merely extends this, only it does so into an area our minds have no everyday experience of.

pervect

This sounds like a recipe for confusion to me. There's some confusion about whether someone sitting in a chair is "accelerating" or "at rest", if you view him as accerating he's changing inertial frames, and therefore travelling through "different" realities, as he sits there. It seems very clear that anyone who is actually accelerating must be considered to be travelling through "different" realities, whether it's in a rocket ship, or a car.

It's really easier to concentrate on what doesn't change than what does. Length and time do change between observers, that's why it is better to focus on what doesn't change between observers, is the Lorentz interval.

To some extent this discussion is philosophical, but I will say that it's a lot simpler, in my opinion, to focus on the invariants of special relativity, the Lorentz interval, and to use those as the basis for a shared "reality", rather than to consider that every observer has his own "reality".