Public Service Broadcast:

THE MEASUREMENT PROBLEM IN PHYSICS

Introduction :

The most famous fruit in physics is an apple, but the most famous animal in physics is a cat. It belongs to Edwin Schrödinger, a theoretical physicist who in the early 20th century helped to develop the radical theories of Quantum Mechanics. Schrödinger’s cat does not actually exist – it is the subject of a thought experiment – in which the rules of quantum mechanics make it appear both dead and alive at the same time.

The problem of a cat that is both dead and alive illustrates the challenges of quantum physics and at the heart of this apparent absurdity is a thing called the measurement problem.

The measurement problem arises because we don’t really understand how the atoms that constitute our world behave. They are fundamentally mysterious to us, even shocking, and they defy our attempts to measure and make sense of them. Possible solutions range from the existence of multiple realities to the rather more mundane possibility of an error in our mathematics - but a solution, if found, could transform our understanding of reality.

Transcribed from the last 10 mins or so of the broadcast
B. Hiley
We seem to be in a bizarre position.

We somehow have to do particle physics all over again. 50 – 60 years of work, thousands of physicists, collaborative work, all those Nobel prizes that were awarded – we’ve got to do the work all over again. It just seems insane – it just doesn’t happen in physics. So this is in a very strange situation that we are in, we know how to solve the measurement problem. The community of physics have voted with their feet otherwise.

R.Penrose
I just want to comment: the fact that we have to do the physics all over again is no argument against. I point out, this has happened before, it’s not unprecedented. It happened with Einstein’s theory general of relativity: We had a completely different view point with regard to space and time. And you might say, we have to do all the physics, all over again – but we do, strictly speaking! But at least Einstein’s theory / first of all, there are approximations where you can get away with using Newtonian theory most of the time. But it’s really a completely different outlook and it tells us that gravity is not a force in the ordinary sense of the word. And I think were looking towards a revolution of that kind. It has to be something which does overthrow all of our standard views about particles and so on. It may not affect what people do in detail.

Basil Hiley
I’m all for revolutions in physics – but one expects new phenomena.

S. Saunders
The situation in quantum mechanics is that we don’t. We don’t have new phenomena or anomalies. We do have the problem of how to reconcile quantum theory with gravity . . .

M. Bragg
Can I just move on one more step, before we move on. There’s another solution that shows that Schrödinger’s equation is a complete description of reality and that’s what it is. And the Wave Function does not collapse and there’s a many worlds solution to this. Could you explain to our listens what that is.

S. Saunders
The many worlds interpretation was first tabled 50 years age by Hugh Everett. It was crazy. . . it’s the view that the Wave Function indeed never collapses; what we see is only one part of the wave function. Other regions of the Wave Function also have equal reality, equal validity, and there they are, people just like us arguing, debating. Perhaps there’s Saunders who missed his taxi this morning failed to show up; goodness, the whole show was about Pilot Wave Theory and gravitation collapse and many worlds didn’t get a look in. That’s also there in the Wave Function as part of reality

M. Bragg
These things do take every option, so there’s every possible world coexisting at the same time. So there are billions upon billions of worlds, at this moment! Which proves Schrödinger’s theory. And that is one way to say, yes this is fine, we’ll carry this right through and that what it ends up as. The many worlds theory and it has a logic to it and it follows the mathematics. But, it seems Roger Penrose to you, not to make much sense.

R.Penrose
There are two levels which it does, of course it’s a crazy theory, but that shouldn’t in itself be a reason against it, as we know. But I think the problem with it; what we really need, it’s not really finished, in my view. I mean, O.K maybe all these different worlds do exist simultaneously; the cat is alive and dead in two separate worlds, if you like. I think the trouble, really with it, is not it’s craziness, but that it’s not a completed theory. You need one of two things, either a theory of real physical behaviour, which this is not, the world we seem to see, it’s there and the other worlds are there at the same time. But if we don’t have a theory of real physical behaviour which mirrors what we see; the cats alive or dead. It therefore has to be a theory of experience. The theory has to tell us why a person like you or me would only see a live cat and not a super position of a live or dead cat Why doesn’t experience allow you to perceive this super position of different worlds and what we only see is one world. So you need a theory which somehow gives us that.

S. Saunders
This is a very long history of introducing questions of consciousness, the mind, into quantum physics and the problem of many ones. I think there was a time when the many one interpretation was susceptible to criticism. But I think the way it’s been developed over the last twenty years or so – it really is, it’s the wrong objection to make. The claim is and this is my own interest in many worlds.
Take the Schrödinger equation, study it for complex structures and use just standard methodology in the special sciences to extract from it, interesting structures, interesting high level emergent phenomena. And the claim on the table is that, doing that, you do see in the Wave Function macroscopic, stable things; objects, cats, people, chairs, tables. You see all of that stuff, it’s there in the physics. And it’s there in a way such as they can’t couple with one another. These things are dynamically disassociated from one another.
Now if you’ve got all that, if you’ve got the chemistry right, decoupled in one region of the wave function from another. If you’ve got the molecular physics right: You can get all of the rest out later.

Melvin Bragg, Broadcaster

Basil Hiley, Emeritus Professor of Physics at Birkbeck, University of London

Simon Saunders, Reader in Philosophy of Physics and University Lecturer in Philosophy of Science at the University of Oxford

Roger Penrose, Emeritus Rouse Ball Professor of Mathematics at the University of Oxford


Is it not worthy of tears that, when the numbers of worlds is infinite, we have not yet become Lords of a single one. ~ Alexander the Great

Physics (Greek: physis – φύσις meaning "nature") is a natural science; it is the study of matter[1] and its motion through spacetime and all that derives from these, such as energy and force.[2] More broadly, it is the general analysis of nature, conducted in order to understand how the world and universe behave.[3][4]

Physics is one of the oldest academic disciplines, perhaps the oldest through its inclusion of astronomy.[5] Over the last two millennia, physics had been considered synonymous with philosophy, chemistry, and certain branches of mathematics and biology, but during the Scientific Revolution in the 16th century, it emerged to become a unique modern science in its own right.[6] However, in some subject areas such as in mathematical physics and quantum chemistry, the boundaries of physics remain difficult to distinguish.

Physics is both significant and influential, in part because advances in its understanding have often translated into new technologies, but also because new ideas in physics often resonate with the other sciences, mathematics and philosophy.

For example, advances in the understanding of electromagnetism led directly to the development of new products which have dramatically transformed modern-day society (e.g., television, computers, and domestic appliances); advances in thermodynamics led to the development of motorized transport; and advances in mechanics inspired the development of calculus.



Kristine

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