5 thoughts on “Biggest ideas in the universe – Sean Carroll chats concepts”

1. Re Sean Carroll’s YouTube video “The Biggest Ideas in the Universe | 5. Time” (Apr 21, 2020): “We talk about what time is, whether it’s ‘real,’ and about why it seems to move in just one direction.”

   Time-ly

   time, time, what has become of you?
   Newton looked around and saw eternity –
   was there really anything new?
   entropy was so hard to see,
   so many bits to be.

   past-present-future such a totality,
   a 4D map in general relativity.
   time travel some possibility,
   back and forth invariantly?
   the present so easy to see.

   we came from so different spaces,
   that moment we met full of memory,
   in uncertain times and real places,
   only passing so inevitably,
   the plan was so hard to see.

   i wanted to scatter the past, no block verse,
   our clocks dividing moments distinctly,
   sometimes repetitious, you spoke so terse,
   being together so practically,
   the future was so hard to see.

   did our trains pass coincidently
   as coffee swirled in your cup,
   or not so absolutely?
   micro changes just messing up
   what was so hard to see.

   if we replayed our flicks backward
   was everything just too free?
   when did we stop moving forward
   from a start in low entropy?
   our trajectory was so hard to see.

   like labeled ticks on our flicks
   becoming full of ambiguity,
   the changing scenes of our picks
   passing in time’s crazy tapestry,
   in the arrow of time will you remember me?

2. Re Carroll’s YouTube video “The Biggest Ideas in the Universe | 6. Spacetime” (Apr 28, 2020): “This is … about the major idea underlying special relativity – that both space and time are different parts of one unified, four-dimensional spacetime.”

   Spacetime-ly

   we’ll circle back to an energy ride,
   but first let’s talk more classically
   about spacetime and the limit C.
   why the idea of union counts aside
   from space and time as separately.

   it’s really about relativity,
   theories special & general clearly.
   we’ll be presenting top-down Minkowski’s 4D
   (not starting with Newton’s universality)
   then get back to how everyday we see.

   gone Newton’s space and time so absolutely,
   not just adding a coordinate to three,
   when we travel from point A to B.
   a new structure mathematically,
   paradoxes go away conceptually.

   how is going A to B in some ways
   like traveling along in space 3D?
   a clock’s elapse not coordinately,
   and light cones demonstrate how spacetime plays,
   all proper time intervals will agree.
   (but order may not so easily
   if moving non-inertially)

   [chorus]
   spacetime’s a dynamic,
   there’s no need to panic,
   when shifting into space-like,
   traveling less as time-like,
   moving straightly’s not the trick

   maybe you’ve heard the twins paradox gaveled.
   one rocketing far to Alpha Centauri,
   even prized Feynman got this incorrectly –
   the spacetime path distance that’s traveled,
   not acceleration as the key.

   so how match those cones to normality,
   where coordinate time is all we see.
   a light-year unit shifts dramatically,
   while by second closes on horizontally,
   a surface like Newton’s apparently.

   the beauty of unification arises
   full of various surprises:
   as length contracted, time stretched,
   a common origin fetched,
   energy and momentum unifying.

   but our vision is not yet complete,
   paradigm aligned classically,
   predicting where all the stuff will be.
   quantum mechanics is a strange treat,
   and merging gravity so trying.

3. Re Carroll’s YouTube video “The Biggest Ideas in the Universe | 7. Quantum Mechanics” (May 5, 2020): “This installment runs down the basic ideas …”

   Is it possible to declutter quantum field theory (QFT) of legacy baggage? A way to better avoid classical rabbit holes?

   What I’d like to see is a “top-down” a-historial presentation starting with a lean QFT, and taking that seriously – all-permeating energy fields sans any point-particle tone. Then unpacking a wave-like mathematical formalism. Would that just get the Standard Model?

   I’d be interested in a sparse energy framework: (1) perhaps with some structural (sandwich) model like Frank Wilczek’s Grid, and (2) a relational model like Lee Smolin’s for properties like charge and mass – seeking to eliminate unnecessary intrinsic properties.

   I’d be interested in a toy model for the interplay of field and vacuum energy – a case for equal footing as energy counterparts. Space as a “roiling soup” of vibrations. Frothy fields and foamy vacuum. And how that energy is bundled, and the field dynamics when those bundles are confined, perhaps based on Grid coupling (superpositions like Don Lincoln’s analogy of adjacent tuning forks).

   I’d be interested in, for example, starting with the electron field, the photon field, up/down quark field(s), and the gluon field(s). And excitations, localized vibrations, superpositions. The positron field the same as the electron field – positrons as reverse excitations. Whatever “reverse” (or equal-and-opposite) may mean.

   I’d be interested in 3D visualizations of Fourier transforms. If I could visualize a “ripple, or excitation, or bundle-of-energy” in a field – with all the relevant properties, then maybe a “reverse” excitation would be straightforward, eh.

4. Re Sean Carroll’s YouTube video “The Biggest Ideas in the Universe | 9. Fields” (May 19, 2020), here’re my reactions.

   It’s all about energy.

   Is there an alternative to viewing a quantum field as a superposition of an infinite number of harmonic oscillators?

   And, can we really separate the vacuum from quantum fields? If entangled to some degee? We typically abstract them as superpositions – as like layers; but for an entangled system, the wave function associates amplitudes with the entire configuration of the system, not part-by-part. (And any isolated system is only an approximation.)

   In some sense, I’d be interested in starting with an entangled interactive energy “fabric” and then how fields emerge and then how those modes get us to talking about particles as stable modes (and observables).

   If the energy density function is not merely a superposition of separable wave functions – the vacuum-energy wave function and the fermion-energy wave function, … then there’s just one amplitude. Not adding amplitudes of two wave functions.

   Energy density function = wavefunction(E-vacuum + E-field)

   Energy density function ≠ wavefunction(E-vacuum) + wavefunction(E-field)

   No infinite gradients.

   Then we predict energy density probabilities, which can be decomposed into modes which have modes themselves and which have properties of interest.

   Do Feynman diagrams, as visual tools, use vacuum energy in an ad hoc way? As an add-on perturbative device which simplifies computing interactions. As such, a successful approximation (at least in QED vs. QCD), but sidestepping entanglement of vacuum and fields?

   Does entanglement create spacetime?

   References

   Wave function

   Hilbert space

5. I enjoyed the wrap-up to “The Biggest Ideas in the Universe | 10. Interactions” (May 26, 2020). The “what to do about the energy density of empty space” is what intrigues me. As well as ways to do 3D visualizations of localized field interactions, like a electron vibration and “reverse” vibration (positron) annihilating.

   (transcript quote) … that’s why I say the Feynman diagram is a story. there is a true story, which is what is the amplitude for a certain reaction to happen, but the intermediate steps are calculational devices. you kind of know that has to be true because the real process that you’re looking at is the sum of all of these different diagrams and all the different diagrams have different sets of virtual particles in them. they’re not exactly the same. so Feynman actually … so anyway but that’s … that is the way of thinking about Feynman diagrams: they’re … they’re calculational devices for doing calculations in quantum field theory.

   I just don’t want you to take all of the steps along the way overly literally. okay, including the virtual particles in between.

   Now, I’ll reveal that Feynman when he was inventing this – he had an aspiration. he was hoping that he was not coming up with a set of calculational tools to do quantum field theory better. he was hoping that he was replacing quantum field theory with a good old fashioned particle theory. the theory of particles that be created or destroyed, following the rules of these Feynman diagrams. turned out not to be right.

   Again, many missteps along the way to any great idea, and it turns out this is a way of thinking about quantum field theory, not a replacement for it. part of his motivation was the cosmological constant problem. remember, we talked last time about the fact that when you have fields pervading the whole universe, these fields have energies and the energies can be added up; and if you just do it naively, the quantum mechanical contribution to the energy of empty space is infinitely big.

   And this is one of those things that physicists have known for a long time; but before around the 1980s, they didn’t worry about it that much. But some people did. so Feynman worried a little bit about it. Philip Andersson worried about it a little bit for different reasons. But they thought that this was a problem with quantum field theory. right, that it gave an infinite energy density to empty space. if you could replace the fields with particles you could get rid of that infinite energy.

   It didn’t work. so we are left with both this wonderfully accurate calculational device of Feynman diagrams and this somewhat unnatural formalism of quantum field theory. we don’t know what to do about that. we didn’t … I’m not gonna reveal what to do about that.

   We still don’t know what to do about the energy density of empty space. But we’re thinking, and it might be that we do in one way or the other have to replace quantum field theory. But in the mean time it is absolutely the best way we have of understanding nature currently available.

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