Holiday Message 2020 | The Screwy Universe

Sean Carroll's Mindscape: Science, Society, Philosophy, Culture, Arts, and Ideas

Sean Carroll | Wondery

Society & Culture, Physics, Philosophy, Science, Ideas, Society

4.8 • 4.4K Ratings

🗓️ 21 December 2020

⏱️ 91 minutes

🔗️ Recording | iTunes | RSS

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Summary

Welcome to the third annual Mindscape Holiday Message! Just a chance for me to be a little more chatty and informal than usual, although as it turned out this isn’t all that different from a conventional solo episode. With the difference that what I’m talking about — a phenomenon called “cosmic birefringence” — has played a big part in my personal scientific career, so I get to be a bit autobiographical.

Every photon has a direction of polarization, which generally remains fixed as the photon travels through space. Birefringence is an effect by which the polarization rotates rather than staying fixed. It can happen in materials, but generally not in outer space. But there are exotic physics ideas that could cause such a rotation, including the dynamical dark energy candidate known as quintessence. People have put limits on such cosmic birefringence for a while now, but recently there was a claim that there might be a nonzero amount of birefringence visible in the polarization of the cosmic microwave background! Still very tentative, but if this hint turns into real evidence, it would big extremely big news for our understanding of physics and cosmology, possibly helping us pinpoint the nature of dark energy.

Show notes, links, transcript: https://www.preposterousuniverse.com/podcast/2020/12/21/holiday-message-2020-the-screwy-universe/

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Transcript

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0:00.0	Hello everyone, welcome to the annual holiday message from the Mindscape podcast.
0:03.8	I'm your host, Sean Carroll.
0:05.4	Those of you who've been listening for a while know that we have a pattern near the end of the year.
0:09.3	I roughly speaking take two weeks off around Christmas and New Years, where I don't do either a
0:15.2	regular podcast or an Ask Me Anything episode for those who support on Patreon.
0:20.2	And the last podcast of the year, rather than me interviewing someone or doing some kind of
0:25.3	formal careful solo episode, I just do a holiday message. And the holiday message, I think my
0:31.6	original idea was it would be 10 minutes long and I would say some of the highlights of what
0:36.4	had happened during the year and so forth. But as happens when I do things, it's sort of expanded.
0:42.4	And now sort of I pick a topic that is much more casual and maybe more personal than a little
0:48.4	bit less intellectual perhaps than some of the things I would normally do on the podcast. I just
0:52.7	chat about it. Okay. So I'm not going to get much of an overview of the year here. It's been quite a
0:57.8	year 2020 in various ways. I'm not going to go into that. You've probably had various ways in which
1:03.4	it's been quite a year for you too. So you can imagine just running through the highlights yourself.
1:09.3	Instead, I thought I would take this opportunity to talk about part of the practice of doing science.
1:16.4	In particular, I'm going to talk about the phenomenon known as the screwy universe.
1:20.8	This is the idea that photons, admitted from distant galaxies or the cosmic microwave background
1:26.7	very, very far away, can actually be rotated as they travel through empty space. Let me be clear, sorry,
1:33.7	the let me be, let me be correct. First, the polarization of these photons can be rotated as they
1:39.4	travel through empty space. So a photon, you know, can be thought of as an electromagnetic wave,
1:44.0	right? And an electromagnetic wave is literally an electric field oscillating up and down
1:49.6	and a magnetic field oscillating backward and forward perpendicular to the electric field.
	...

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