MWI: Many Worlds interpretation of quantum mechanics explained | featuring Sean Carroll

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The many worlds interpretation of quantum mechanics was put forth by graduate student Hugh Everett in 1957. It was considered preposterous at the time, but is now going mainstream. It requires us to change our paradigm about our experience of reality, and consider that there may be many worlds where every possible quantum outcome happens. And that we are living in just one of those branches of the universe at any one moment.

I spoke to the authority on this subject: Prof Sean Carroll of Caltech. That interview along with the explanation and comparison of the Many Worlds interpretation compared to the Copenhagen interpretation is featured here.

the Copenhagen interpretation was championed by Neils Bohr in the 1920’s. It suggests that objective reality doesn’t exist until it is observed or measured. The quantum world is governed by a set of probabilities as described by a wave function that evolves over time in the Schrodinger equation. The act of measuring forces the set of probabilities to randomly assume only one possible value.

But the many worlds interpretation says that the entire universe is in a state of superposition. A measurement may look like a particle has some set of properties, but that is not the overall reality. It posits that the world splits every time we THINK a quantum measurement is made. And that although we may see one thing in our world, there is another world in which another thing has occurred.

So for example, if we are trying to measure the spin state of an electron, the MWI says that our measuring device becomes entangled with the electron. This causes something called decoherence. The decoherence splits the universe in two such that in one universe the device measures spin up, and in the second universe, the device measures spin down. Both universes exist. We just happen to experience one of these universes. We could just as well be in either universe.

And similarly, this kind of decoherence is happening all the time. And in every instance this happens, the universe splits. So this is why it is called many worlds, because many such branches or splits of the world exist simultaneously.

In the Copenhagen interpretation, there are two sets of rules. One set of rules applies to systems prior to measurement, and a different set of rules applies for systems after measurement.

The many worlds interpretations says, no, this is not the way the universe works, that there are only one set of rules that abide by and evolve over time according to the Schrodinger equation. And there is no randomness because all possible outcomes are a branch of the many worlds.

The Good points about the MWI are:
1) it gets rid of measurement problem.
2) It lets us apply quantum mechanics to the entire universe.
3) there is no randomness.

The bad points about MWI are:
1) How does branching occur?
2) How is energy conserved.
3) Why do we see only one world, if the other worlds are equally present?

Branching occurs by decoherence, which is not quite like wave collapse. It can be thought of as a loss of information to the environment. When an isolated quantum system like say an electron gets entangled with its environment like photons and other molecules that may be present, this has the effect of a transfer of quantum information. All of the photons and atoms that bounce off the electron are agents of decoherence, and can fix its position in space and give it a sharp outline.
This is decoherence and causes the branching. This is how quantum systems can start behaving like classical system.
#quantummechanics
#manyworldsinterpretation
#quantumphysics

The total energy of the universe and all its branches is conserved analogous to the way that the all the individual probabilities inherent in the Schrodinger equation add up to one.

I asked Sean Carroll about that, and he, like me, hates that idea. I myself think that physics is more than calculations, it is a science that tries to get at the truth about what the true nature of reality actually is. That’s what we should really be after, I feel. And that pursuit at least on this channel will always exist.

Видео MWI: Many Worlds interpretation of quantum mechanics explained | featuring Sean Carroll канала Arvin Ash