Leonard Susskind: String Theory, Fine-Tuning, and the Physics of the Multiverse

Leonard Susskind is Felix Bloch Professor of Physics at Stanford University. Among other accomplishments, he is among the fathers of such revolutionary concepts in physics as string theory, black hole complementarity, the holographic principle, and the string-theoretic landscape. It is this last concept that Robinson and Leonard discuss in this episode. More particularly, they address the fine-tuning problem—that so many of the constants in physics, such as the cosmological constant—appear to have been selected precisely to allow for human life, as if they were substantially different we would not exist. In answering this question they talk about string theory, dark energy, the Higgs boson, god and supernatural explanations, eternal inflation, the multiverse, the interpretations of quantum mechanics, the anthropic principle, alternative answers to the problem, and the future of research in the area. For more detail, read Leonard’s book on the topic, The Cosmic Landscape.

OUTLINE
00:00 Introduction
04:03 A Parable About the Fine-Tuning Problem
09:58 String Theory and the Fine-Tuning Problem
18:04 The Problem of Dark Energy
25:05 Could Dark Energy Rip the Universe Apart?
33:11 God, String Theory, and the Illusion of Intelligent Design
42:51 On the String-Theoretic Landscape
48:54 The Eternal Inflation of the Universe
55:07 What Determines the Physics of the Multiverse?
01:02:09 On the Interpretations of Quantum Mechanics
01:05:50 On the Future of String Theory and Fine-Tuning

Robinson Erhardt researches symbolic logic and the foundations of mathematics at Stanford University. Join him in conversations with philosophers, scientists, and everyone in-between.

[emptyeff]

I’m commenting now just to say hell yeah Robinson. Susskind is a legend, glad you’ve gotten him on. Also, shout out Jenni’s brambleberry crisp.

[rtt]

Very good interview. I appreciate how the interviewer let Susskind talk at length, not interrupting. Great.

[jozincarnate]

Thankyou, so much Robinson. Having a fresh up to date interview with one of History's giants is, great to see. Hearing the legend Professor Susskind, (who is such an inspiration to me) still show his love of problem solving, critical thinking, and rational mind, is still so much fun for him is just he icing on the cake. I hope any young minds watching, following in Professor Susskind's greatness, get inspired to become modern-day explorers; and to seek out new math and new logic, to boldly go where all mysteries will finally become known.

[blingpup]

Lenny is a legend!! Robinson, you’re killing it with these top tier guests!

[hmdshokri]

explaining it simple and not distort the core idea is a difficult job, Susskind is a master of it.

[Prabhakar-gfoq]

I am always fascinated by Prof Suskind, his brilliant intellect, his humility and giving credit where it belongs and his ability to explain some of the most complex concepts in a way even a person like me can understand make him unique. Given enough time as he says anything is possible, I pray he will live long enough to see his string theory proven and awarded a Nobel prize.

[Goldslate]

I cannot begin telling you how much this was needed. He is the reason I love doing physics, regardless of the momentary difficulties sometimes. Thank you, Rob and thank you, Professor Susskind. You're the best...

[NunTheLass]

Such a wonderful teacher. I must have watched a hundred lectures of his over the past 15 years. The submarine metaphor was nice. The universe is the way it is because if it were different, there would *probably* be nobody around to ask why the universe is the way it is. Got it!

[bernardofitzpatrick]

Professor Susskind in Robinson’s clarity and profundity enabling warm crucible of ideas and truth seeking! Quality right there! Prof Susskind the legend. His use of the word “fun” in connection with his adventures in the cosmological wonderland is a testimony to his ongoing, unending curiosity and joy in the search for understanding . Thank you, as always, Robinson.

[themaximus]

These new in person interviews have me so excited

[AdrianBoyko]

Forget physics, Susskind is genius of common sense.

[kdalkafoukis]

I wish to Susskind a long life. He is one of the GOATs. Every lecture that I have watched is mind blowing. Also the fact that he combined complexity theory with physics shows that he looks so far away.

[CoreyChambersLA]

Cannot deny the unique fiction writing talents of Susskind. Here are 12 alternative approaches or theories that seek to address the same fundamental issues as string theory:

Loop Quantum Gravity (LQG):
LQG is an approach to unifying quantum mechanics and general relativity without invoking string theory. It posits that space-time is quantized and has a discrete structure at the Planck scale.
Causal Dynamical Triangulations (CDT):
CDT is a background-independent approach to quantum gravity. It constructs a quantum space-time geometry by summing over all possible triangulations of space-time.
Asymptotic Safety:
Proposed by Steven Weinberg, this theory suggests that gravity is "safe" from divergences at high energies, meaning it can be described by a non-trivial ultraviolet fixed point.
Emergent Gravity:
This concept suggests that gravity is not a fundamental force but rather an emergent phenomenon arising from more basic microscopic interactions.
Twistor Theory:
Developed by Roger Penrose, twistor theory reimagines the structure of space-time, using complex number geometry to unify general relativity and quantum mechanics.
Entropic Gravity:
Proposed by Erik Verlinde, this theory suggests that gravity arises as an entropic force—a macroscopic statistical effect rather than a fundamental interaction.
Noncommutative Geometry:
In this approach, the coordinates of space-time are promoted to noncommutative operators, leading to a modified version of quantum field theory that incorporates gravity.
Horava-Lifshitz Gravity:
This theory modifies general relativity to make it renormalizable by introducing anisotropic scaling between space and time at high energies.
Quantum Graphity:
This model posits that space and time are not fundamental but instead emerge from a network of discrete, interacting nodes.
Spin Foam Models:
Spin foam models extend the ideas of loop quantum gravity by describing the evolution of quantum states of space-time as a sum over possible "foams" or configurations.
Matrix Models:
These models, such as the BFSS matrix model, aim to describe the fundamental degrees of freedom of string theory using large matrices, suggesting a non-perturbative definition of the theory.
Holographic Principle and AdS/CFT Correspondence:
Although closely related to string theory, the holographic principle and its realization in AdS/CFT suggest that the universe can be described by a lower-dimensional theory, which challenges the need for extra dimensions as in traditional string theory.

[dosesandmimoses]

I enjoy Dr. Susskind’s lectures. Thank you gentlemen for your discussion..

[snjsilvan]

Great to see him again! Thank you, Dr. Susskind for all your work and teachings!

[ivocanevo]

I didn't know you existed, Robinson. But you're doing long form interviews of my favourite thinkers, you ask good questions and you're in the comments. That deserves an enthusiastic subscription. Look forward to more.

[AdamT]

I’ve watched 10^500 videos about string theory but this one was the first to explain it in a way that made any kind of sense to me. His examples and stories were excellent. Thank you.

[spencerwenzel]

This has been my favorite episode so far and the best treatment of fine tuning I have ever discovered. Thanks for this Robinson!

[ldero]

This is the best interview I have seen in years about cosmology . Just a big Wow !

[CurtOntheRadio]

I like listening to Professor Susskind. He's done ok for a plumber. Lucky you, Robinson, meeting all these amazing people. I imagine it's often as intimidating as it is fascinating, not least in this case.

Anyway, thanks so much. My bedtime listening sorted.