Search Episodes
Listen, Share, & Support
Listen to the latest episode
Subscribe via iTunes
Subscribe via RSS
Become a fan
Follow on Twitter

Support Us:

Please consider making a donation to help make this podcast possible. Any contribution, great or small, helps tremendously!

Subscribe to E-Mail Updates

Related Readings
  • Answers for Aristotle: How Science and Philosophy Can Lead Us to A More Meaningful Life
    Answers for Aristotle: How Science and Philosophy Can Lead Us to A More Meaningful Life
    by Massimo Pigliucci
  • Nonsense on Stilts: How to Tell Science from Bunk
    Nonsense on Stilts: How to Tell Science from Bunk
    by Massimo Pigliucci
  • Denying Evolution: Creationism, Scientism, and the Nature of Science
    Denying Evolution: Creationism, Scientism, and the Nature of Science
    by Massimo Pigliucci

RS133 - Sean Carroll on "The Many Worlds Interpretation is probably correct"

Release date: May 3, 2015

Sean CarrollIn this episode of Rationally Speaking, Caltech physicist Sean Carroll describes an "embarrassing" state of affairs in modern physics: that we still don't know how to interpret quantum mechanics, almost a century after its discovery. Sean explains why he thinks the "Many Worlds Interpretation" (MWI) is the most plausible one we've got, and Julia explores his thoughts on questions like: Can MWI be tested? Is it "simpler" than other interpretations, and why? And does MWI threaten to destroy our systems of ethics?

Sean Michael Carroll is a research professor in the Department of Physics at the California Institute of Technology. He is a theoretical cosmologist specializing in dark energy and general relativity.

 Sean's pick: "Quantum Computing since Democritus"

NEW: Full Transcripts 

Reader Comments (4)

Why am I the only one making a comment??!
I ended up writing a *really* long response – rather off the cuff – on my own blog:
If anyone actually makes it through the entirety of my ramblings, you probably deserve some sort of trophy.
May 18, 2015 | Unregistered CommenterCEF
Okay, I didn't earn the trophy. But I can see you have asked some of the important questions.

However, I'm not sure you have exactly undermined Carroll's claims, just erected signposts pointing to ways others might try to undermine them.

For example, he says that the many worlds are already there in the formalism, and Many Worlds just takes those seriously. You suggest that this assumes a naive realist interpretation of the Quantum equations. But ... surely some sort of realist interpretation needs to connect to at least the world that we turn out to be in. I thought that was Carroll's whole point: that non-Many Worlds interpretations have to treat one of the possibilities as special, while the Many Worlds interpretation doesn't. So it's more parsimonious.

As you say, it's hard to accept the reality of complex numbers. But I've worked with acoustics and Fourier transforms, and however odd the math is under the hood, it clearly offers real solutions - real in the mathematical sense, and real in the engineering sense.

I am inclined to accept QM probabilities in the same way: not only is "conventional" probability odd, but as I recall QM probabilities are not limited to being real numbers between 0 and 1. Just because we can't grasp the "real" meaning of the successful equations doesn't mean they don't describe reality.

Anyway, I'm already working at the limit of my understanding of this stuff. I'd love to see someone as articulate and knowledgable as Sean Carroll argue another alternative - see if I can at least follow the gist and if they have more substantial arguments against Many Worlds than Sean Carroll has for Many Worlds.

I should acknowledge that the closest I've come to feeling I understand this was actually reading through Eliezar Yudkowski's series about QM on the Less Wrong site (, and he clearly favours Many Worlds.

Julia (if you read the comments), this feels like a true scientific debate, and I'd love it if you got someone on to respond to Sean Carroll's position from a different camp.
June 9, 2015 | Unregistered CommenterTim Mills
To Tim Mills:

Keep reading CEF. She's got a great handle on this stuff.

I'll make one comment on your post from where you said:

"Julia (if you read the comments), this feels like a true scientific debate,"

It's not a scientific discussion it is metaphysics. Many worlds as proposed makes exactly the same predictions as Copenhagen. There is no difference. In fact that is the best that one can say about it - IT MAKES NO DIFFERENCE.
June 9, 2015 | Unregistered Commentervector shift
I suppose I could have said, "It sounds like an interesting debate with valid arguments from different scientific perspectives." Or, "It's an interesting discussion about points that are interesting to people who perform and consume science."

But the fact is, science isn't just engineering. It isn't just about making predictions and getting things to work at a practical level. It's an attempt to <i>understand</i>. Two explanations may be equally predictive, but differ in ways that are important to scientists and (I maintain) to science.

For example, an explanation that says "E=mc^2" is more elegant than one that says "E=mc^2 and the sky is beautiful". The addition, if it doesn't affect predictions, doesn't diminish the theory's predictive utility. But it's a ridiculous thing to include. Yes, that is an aesthetic judgment. But Occam's Razor - and its highly-refined modern mathematical descendents - are useful. It seems to me that one of Sean Carroll's key points is that Many Worlds is a more parsimonious, elegant, or efficient interpretation of the data and the equations than Copenhagen.

Now, if you don't care about parsimony, that's your right. But parsimony is certainly part of what scientists attend to - what they <em>ought</em> to attend to - when they're doing science.

Even further than that, I would say there is a practical utility when it comes to, for example, teaching a theory. I have found the Many Worlds interpretation makes the whole structure of quantum mechanics easier to grasp than the Copenhagen interpretation. I don't know how far that advantage would take me if I were to try learning the math, but again, I think that's a valid question worth discussing. And since teaching science is indisputably an important part of doing science, the question of what is the most effective way to teach science is an important one to discuss.

So, to the extent that there is a valid discussion around the relative parsimony of the predictively-equivalent models (Copenhagen vs Many Worlds), I stand by my claim that it is a <em>true scientific debate</em>.
June 10, 2015 | Unregistered CommenterTim Mills

PostPost a New Comment

Enter your information below to add a new comment.

My response is on my own website »
Author Email (optional):
Author URL (optional):
All HTML will be escaped. Hyperlinks will be created for URLs automatically.