[Communicating science series]
While we’re all doing stay-at-home, theoretical physicist Sean Carroll created a chat-from-home series on his YouTube channel. Usually each informal talk (so not lecture-like organization) has a followup Q&A video.
The Biggest Ideas in the Universe is a series of videos where I talk informally about some of the fundamental concepts that help us understand our natural world. Exceedingly casual, not overly polished, and meant for absolutely everybody.
• The Biggest Ideas in the Universe | 10. Interactions (May 26, 2020)
Last time we figured out that when you start with a theory of noninteracting fields and quantized it, you could think of the result as a theory of noninteracting particles.
This is Idea #10, “Interactions.” Last time we dipped a toe into quantum field theory, seeing how quantizing fields leads to particles. Now we let the particles interact with each other, and see how the results are characterized by Feynman diagrams.
• The Biggest Ideas in the Universe | 9. Fields (May 19, 2020)
We’ve talked about the quantum mechanics of particles, now it’s time to apply those ideas to fields. It requires a bit of effort to understand how a quantum field – which is really a wave on top of a wave, when you think about it – ends up looking like particles in the right circumstances. But it’s worth it.
This is Idea #9, “Fields.” A little bit about classical fields, but mostly concentrating on quantum field theory, and in particular on why a quantized field ends up looking like particles. This one is a bit challenging!
• The Biggest Ideas in the Universe | 8. Entanglement (May 12, 2020)
• The Biggest Ideas in the Universe | 7. Quantum Mechanics (May 5, 2020)
• The Biggest Ideas in the Universe | 6. Spacetime (Apr 28, 2020)
• The Biggest Ideas in the Universe | 5. Time (Apr 21, 2020)
• The Biggest Ideas in the Universe | 4. Space (Apr 14, 2020)
The Biggest Ideas in the Universe | Q&A 4 – Space (Apr 19, 2020)
[My notes] Position and momentum – why we live in position space. Phase space and Hamiltonians. State of the system (initial conditions) and carry forward in time. H(x,p) = kinetic + potential. [So, it’s all about prediction.] Example: Simple harmonic oscillator. Partial derivatives.
In physics, a dimension is just a direction to go. How can that be small? “Small” means you can only go so far. (Small distances correspond to high energies.) Planck scale not be able to see at all.
Background on string theory. Particular theories. Bosons, fermions. Dimensions: 26, 10, 11 – bosonic, superstrings, supergravity (a version of gravity which is supersymmetric, with 2-branes). M-theory. Compaction of dimensions (compactification) vs. branes. Gravity cannot be confined to a brane (it’s a feature of spacetime itself). So far hypothetical (no predictions confirmed).
Locality & holography. Black holes. When gravity becomes important. Information and entropy. Locality violated? When gravity is strong, locality is an approximation. (We take locality for granted.)
Indirect observable effects of extra (invisible) dimensions? Generations of particles <-> the size and geometry of the extra dimensions in principle. The energy density of the vacuum might depend, for example, on the extra dimensions.
• The Biggest Ideas in the Universe | 3. Force, Energy, and Action (Apr 7, 2020)
This is Idea #3, “Force, Energy, and Action.” Already I have backslid on my idea that every idea would be encapsulated in just one word, but these three seemed to flow together.
• The Biggest Ideas in the Universe | 2. Change (Mar 31, 2020)
This is Idea #2, “Change.” Which is a less-threatening way of saying “Calculus,” which is the mathematics of continuous change.
The Biggest Ideas in the Universe | Q&A 2 – Change (Apr 4, 2020)
• The Biggest Ideas in the Universe | 1. Conservation (Mar 24, 2020)
[Correction: at 17:51 I say kinetic energy is a vector, I meant to say “scalar.” Kinetic energy has a size, but doesn’t point in a direction.]
In this installment – the very first idea we cover! – I talk about “Conservation.” The idea that a certain property, like momentum or energy or electric charge, stays the same over time. In my view, realizing that this is true – and the corollary, that the world naturally moves, rather than needing something external to keep it moving – represents the real transition between pre-modern and modern physics.
The Biggest Ideas in the Universe | Q&A 1 – Conservation (Mar 29, 2020)
Errata: at 7:23 I say “equilateral” triangle when I really just meant “right” triangle. (Also isosceles.)