Lex Fridman Podcast
#359 – Andrew Strominger: Black Holes, Quantum Gravity, and Theoretical Physics
15 Feb 2023
Andrew Strominger is a theoretical physicist at Harvard. Please support this podcast by checking out our sponsors: - Eight Sleep: https://www.eightsleep.com/lex to get special savings - Rocket Money: https://rocketmoney.com/lex - Indeed: https://indeed.com/lex to get $75 credit - ExpressVPN: https://expressvpn.com/lexpod to get 3 months free EPISODE LINKS: Andrew's website: https://www.physics.harvard.edu/people/facpages/strominger Andrew's papers: Soft Hair on Black Holes: https://arxiv.org/abs/1601.00921 Photon Rings Around Warped Black Holes: https://arxiv.org/abs/2211.01674 PODCAST INFO: Podcast website: https://lexfridman.com/podcast Apple Podcasts: https://apple.co/2lwqZIr Spotify: https://spoti.fi/2nEwCF8 RSS: https://lexfridman.com/feed/podcast/ YouTube Full Episodes: https://youtube.com/lexfridman YouTube Clips: https://youtube.com/lexclips SUPPORT & CONNECT: - Check out the sponsors above, it's the best way to support this podcast - Support on Patreon: https://www.patreon.com/lexfridman - Twitter: https://twitter.com/lexfridman - Instagram: https://www.instagram.com/lexfridman - LinkedIn: https://www.linkedin.com/in/lexfridman - Facebook: https://www.facebook.com/lexfridman - Medium: https://medium.com/@lexfridman OUTLINE: Here's the timestamps for the episode. On some podcast players you should be able to click the timestamp to jump to that time. (00:00) - Introduction (06:34) - Black holes (11:37) - Albert Einstein (31:05) - Quantum gravity (35:17) - String theory (46:05) - Holographic principle (54:02) - De Sitter space (59:14) - Speed of light (1:06:02) - Black hole information paradox (1:13:41) - Soft particles (1:22:48) - Physics vs mathematics (1:31:58) - Theory of everything (1:47:20) - Time (1:49:45) - Photon rings (2:05:26) - Thought experiments (2:13:47) - Aliens (2:19:25) - Nuclear weapons
Chapter 1: What is the main topic discussed in this episode?
The following is a conversation with Andrew Strominger, theoretical physicist at Harvard, whose research seeks to shed light on the unification of fundamental laws of nature, the origin of the universe, and the quantum structure of black holes and event horizons. And now a quick few second mention of each sponsor. Check them out in the description. It's the best way to support this podcast.
We've got Eight Sleep for naps, Rocket Money for saving out subscriptions, Indeed for hiring excellent teams, and ExpressVPN for security and privacy on the internet. Choose wisely, my friends.
Chapter 2: What is a black hole and how is it defined?
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Chapter 3: What was Albert Einstein's contribution to the understanding of black holes?
And I should also mention that as always, we're hiring folks to join our amazing team. And if you're interested or know somebody who might be interested, go to lexfriedman.com slash hiring. This episode is brought to you by Eight Sleep and its new Pod 3 mattress. Today is actually an example of a day where It's been a pretty rough one. I didn't get much sleep the night before.
I didn't get much sleep tonight. I had to do a bunch of really difficult work, especially programming work and then reviewing other people's code. I also had to record a podcast. I also had to socialize, which is another kind of challenge altogether. And all of that combines to just this kind of mental state of maybe psychological, physical, all kinds of exhaustion.
And it's kind of incredible how a short nap can fix so much of that. At least can fix the most important aspect, which is once you wake up, you see the world anew. That reinvigorated feeling of gratitude for being alive, for the beauty of the world, for being able to experience the beauty of the world. And a great nap, at least for me, does that just every single time.
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Chapter 4: How does quantum gravity relate to black holes?
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Chapter 5: What is string theory and why is it significant?
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Chapter 6: What is the holographic principle in theoretical physics?
We have an amazing team of human beings that I'm truly proud of, that I'm truly happy to stand besides as we take on the challenges of creative work in this particular podcast and beyond. Basically capturing in video form interesting ideas, interesting people, interesting concepts, whether it's educational, whether it's
beyond maybe educational, almost like exploring the human condition, whether that's podcasts or videos or all that kind of stuff. Anyway, it's an amazing team, and we're always growing it. And to do so, you have to use the best tools for the job. Indeed, to me, is an incredible tool for hiring. They have all kinds of stuff, including Instant Match tool that helps you find quality candidates.
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Chapter 7: What is the black hole information paradox and its implications?
I think ExpressVPN is the best. And you should use it. It works on any device. Again, I'm biased, but the best operating system, Linux, it works on that. It works on your iPhone, Android. It works on Windows and Mac, everything, everything, everywhere. And I should also mention it's super fast on those operating systems too.
Chapter 8: How do soft particles contribute to the understanding of black holes?
Anyway, go to expressvpn.com for an extra three months free. This is the Lex Friedman Podcast. To support it, please check out our sponsors in the description. And now, dear friends, here's Andrew Strominger. You are part of the Harvard Black Hole Initiative, which has theoretical physicists, experimentalists, and even philosophers. So let me ask the big question.
What is a black hole from a theoretical, from an experimental, maybe even from a philosophical perspective?
So a black hole is defined, theoretically, as a region of space-time from which light can never escape. Therefore, it's black. Now, that's just the starting point. Many weird things follow from that basic definition, but that is the basic definition. What is light that can't escape from a black hole? Well, light is the stuff that comes out of the sun, that stuff that goes into your eyes.
Light is one of the stuff that disappears when the lights go off, the stuff that appears when the lights come on. Of course, I could give you a mathematical definition or a physical mathematical definition, but I think it's something that we all understand very intuitively. what is light. Black holes, on the other hand, we don't understand intuitively. They're very weird.
And one of the questions is about black holes, which I think you were alluding to, is why doesn't light get out? Or how is it that there can be a region of space-time from which light can't escape? It definitely happens. We've seen those regions. We have spectacular pictures, especially in the last several years of those regions. They're there.
In fact, they're up in the sky, thousands or millions of them. We don't yet know how many. But the proper explanation of why light doesn't escape from a black hole is still a matter of some debate. And one explanation which perhaps Einstein might have given, is that light carries energy.
You know it carries energy because we have photo cells and we can take the light from the sun and collect it, turn it into electricity. So there's energy in light. And anything that carries energy is subject to a gravitational pull. Gravity will pull at anything with energy. Now it turns out that the gravitational pull exerted by an object is proportional to its mass.
And so if you get enough mass in a small enough region, you can prevent light from escaping. And let me flesh that out a little more. If you're on the Earth, and you're on a rocket ship leaving the surface of the Earth, and if we ignore the friction from the air, if your rocket accelerates up to 11 kilometers per second, that's escape velocity.
And if there were no friction, it could just continue forever to the next galaxy. On the Moon, which has less mass, it's only 7 kilometers per second. But going in the other direction, if you have enough mass in one place, the escape velocity can become the speed of light. If you shine light straight up away from the Earth, it doesn't have too much trouble.
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