Sean Carroll

Is it true that we have these symmetries like Lorentz invariance that we know and love from relativity? From that perspective, I agree. It would seem weird, right? That you would just magically have this invariance where I could now completely switch to a different perspective and get and slice spacetime differently and get just as good, the same laws of physics basically.

Is it true that we have these symmetries like Lorentz invariance that we know and love from relativity? From that perspective, I agree. It would seem weird, right? That you would just magically have this invariance where I could now completely switch to a different perspective and get and slice spacetime differently and get just as good, the same laws of physics basically.

But there's another intuition, which is let's say that I have a theory that does have this invariance, that is Lorentz invariant, that does have the symmetries of relativity built into it. I am 100 percent allowed to pick a reference frame.

But there's another intuition, which is let's say that I have a theory that does have this invariance, that is Lorentz invariant, that does have the symmetries of relativity built into it. I am 100 percent allowed to pick a reference frame.

to pick a decomposition of space-time into space and time to, within the terms of that decomposition, describe what's going on in space and write down equations telling me how it evolves in time. And so there's no obstacle to building entirely symmetric descriptions in a language that is manifestly not symmetric.

to pick a decomposition of space-time into space and time to, within the terms of that decomposition, describe what's going on in space and write down equations telling me how it evolves in time. And so there's no obstacle to building entirely symmetric descriptions in a language that is manifestly not symmetric.

And so we're asking the question, you know, under what conditions does this step-by-step, moment-by-moment building up lead us to something that shares all the symmetries of relativity? And the answer is I don't know. I mean, there's something very nice about the symmetries of relativity. So I'm not in any sense convinced that they couldn't come out generically under some scheme.

And so we're asking the question, you know, under what conditions does this step-by-step, moment-by-moment building up lead us to something that shares all the symmetries of relativity? And the answer is I don't know. I mean, there's something very nice about the symmetries of relativity. So I'm not in any sense convinced that they couldn't come out generically under some scheme.

But I don't actually know. I know people have tried, by the way. At least I am aware of the existence of various papers about the emergence of Lorentz invariance from not obviously Lorentz invariant descriptions. Divimorphism invariance is a very different thing. That's almost automatic. That's basically coordinate invariance. It's hard to not be divimorphism invariant. Or let me put it this way.

But I don't actually know. I know people have tried, by the way. At least I am aware of the existence of various papers about the emergence of Lorentz invariance from not obviously Lorentz invariant descriptions. Divimorphism invariance is a very different thing. That's almost automatic. That's basically coordinate invariance. It's hard to not be divimorphism invariant. Or let me put it this way.

Divimorphism invariance, which for those of you who don't know, is basically coordinate invariance. It's basically saying I can choose whatever coordinates I want, but there's sort of an active and a passive version of that.

Divimorphism invariance, which for those of you who don't know, is basically coordinate invariance. It's basically saying I can choose whatever coordinates I want, but there's sort of an active and a passive version of that.

Changing the coordinates and leaving the underlying system invariant is one way of saying it, but then keeping the coordinates and moving the system is another way of saying it. That kind of sounds more impressive. But... In my mind, diffeomorphism invariance is a real thing, but it's a real thing that is a label that gets attached to descriptions of theories, not to theories.

Changing the coordinates and leaving the underlying system invariant is one way of saying it, but then keeping the coordinates and moving the system is another way of saying it. That kind of sounds more impressive. But... In my mind, diffeomorphism invariance is a real thing, but it's a real thing that is a label that gets attached to descriptions of theories, not to theories.

So I can describe Newtonian gravity in a 100% diffeomorphism invariant way. I don't because it's just more convenient to— treat space and time differently, explicitly, to pick coordinates on time and coordinates on space separately. But I don't have to do that because it's a description statement, not a theory statement. Whereas Lorentz invariance is a theory statement.

So I can describe Newtonian gravity in a 100% diffeomorphism invariant way. I don't because it's just more convenient to— treat space and time differently, explicitly, to pick coordinates on time and coordinates on space separately. But I don't have to do that because it's a description statement, not a theory statement. Whereas Lorentz invariance is a theory statement.

Some theories are Lorentz invariant and some are not, so I would treat those differently. Anyway, yes, I would love to know whether or not Lorentz invariance under some very simple assumptions naturally emerges, and I don't know the answer to that one. Brendan Hall says, To what extent would you agree with this sentiment? You know, I get it.

Some theories are Lorentz invariant and some are not, so I would treat those differently. Anyway, yes, I would love to know whether or not Lorentz invariance under some very simple assumptions naturally emerges, and I don't know the answer to that one. Brendan Hall says, To what extent would you agree with this sentiment? You know, I get it.

I think that you're correct that leisure is now more isolated from our fellow people. Arguably, computers have done that and smartphones even more than TV has. On the other hand, it's given us a whole bunch of enjoyment and entertainment that we didn't used to have. How do I weigh those two things against each other? I truly don't know. My own feeling is that probably TV is a net good.

I think that you're correct that leisure is now more isolated from our fellow people. Arguably, computers have done that and smartphones even more than TV has. On the other hand, it's given us a whole bunch of enjoyment and entertainment that we didn't used to have. How do I weigh those two things against each other? I truly don't know. My own feeling is that probably TV is a net good.