# Equation for theory of everything

leonstavros
Assuming we can come up with an equation that describes the foundamental forces of the universe can we then create a program using the equation to make predictions about the future outcome of the universe? How can quantum uncertainty play role in such outcomes? If the equation can be made to predict future events can it be used to reproduce past events?

Assuming we can come up with an equation that describes the foundamental forces of the universe can we then create a program using the equation to make predictions about the future outcome of the universe? How can quantum uncertainty play role in such outcomes? If the equation can be made to predict future events can it be used to reproduce past events?
Well, according to classical physics, if we had all of the information about the universe at one particular time, then we would, by definition, also know the entire past and future of the universe as well, because any point in time before or after could be calculated from the time for which we know everything.

This breaks down somewhat in quantum mechanics. In quantum mechanics, you have the same sort of thing, but the way in which that information is expressed is as a wave function, and as it so happens, because we are made up of part of that wave function, due to the way quantum mechanics works, it's just not possible to be aware of the whole of it (even with infinitely-powerful information gathering technology and infinite storage capacity). Basically, the wave function in quantum mechanics is necessarily split up into a number of approximately-classical "worlds", all of which are out of contact with one another. And what's more, these worlds aren't static, but tend to branch off. This means that if I know absolutely everything about our semi-classical "world" for the current time, and can thus calculate the entire past, I cannot calculate the entire future: I can only calculate a probability distribution of potential futures.

leonstavros
Basically, the wave function in quantum mechanics is necessarily split up into a number of approximately-classical "worlds", all of which are out of contact with one another. And what's more, these worlds aren't static, but tend to branch off.

Does that mean we live in different worlds at the same time? How many possible worlds are possible? How can we prove if such multiworld exists? If we do exist simultaneously in different worlds are all experiences the same or every one differs? This is somewhat like the movie groundhog day where the protagonist experiences different world outcomes the only difference being he is aware of past experiences and is able correct his behavior to achieve his goal(get the girl).

Does that mean we live in different worlds at the same time?
Well, not really. We only ever observe one world. So while there is a counterpart much like us in a fraction of these other "worlds", those counterparts are different (sometimes only a tiny bit different, sometimes very different, and at some point the distinction breaks down and there is no clear counterpart at all).

How many possible worlds are possible?
The space in which the wavefunction lives is called a Hilbert space. Formally, the Hilbert space is an infinite-dimensional space, which means that there simply is no limit to how many separate semi-classical worlds a wavefunction can describe.

How can we prove if such multiworld exists?
By carefully examining the boundary of collapse: the many worlds interpretation makes very specific predictions of how wave function collapse occurs (through decoherence). This has been done:
http://prl.aps.org/abstract/PRL/v77/i24/p4887_1

If we do exist simultaneously in different worlds are all experiences the same or every one differs? This is somewhat like the movie groundhog day where the protagonist experiences different world outcomes the only difference being he is aware of past experiences and is able correct his behavior to achieve his goal(get the girl).
Each differs by some margin. In some cases, the differences may be so minor that you couldn't tell a difference with even the most sensitive of instruments. In other cases, the differences would be so severe that, for instance, even the low-energy laws of physics may well be very different.

leonstavros
Well, not really. We only ever observe one world. So while there is a counterpart much like us in a fraction of these other "worlds", those counterparts are different (sometimes only a tiny bit different, sometimes very different, and at some point the distinction breaks down and there is no clear counterpart at all)..

Do you think that different versions of us are quantumly entangled?

I've heard of Schroedinger's cat being dead and alive at the same time because of the wave function. Once the observer observes, the wave function collapses to one state. But what if there's multiple observers? How does the wave function know what observer it should respond to?