I am inspired today, once again, by the idea of duality and its fundemental role in our physical reality, from electrical duals, to quantum duals, to the round trip of light (earlier post) and so on...

The more time goes by and the more I think of the world as an expression of Duals (the formal term) the more I realize that duality itself may be the unifying property of the universe that all things emerge from.

I cant help but think that duality is a profound insight of the universe, but I havent quite connected the dots yet... All I know is everything we talk about seems to be only valid in duals and becomes unknowable when we try to seperate those duals in some way...

I am going to call it "The Iron Curtain of Duality"... but I feel like I need to invest time thinking about this, something is there.

@3ammo the problem with that logic is that we already can experementally prove that relativity is correct so any conventional measurement is moot going in.

Moreover the idea that speed of light is a constant is not what is the issue. The speed of light **is** a constant when measured round-trip, that is experimentally provable. What is not a postulate and the part we cant prove is that the speed of light is a constant one-way regardless of orientation. We take that to be the case in relativity as a matter of **convention** not as a postulate. The reason we do so is because even if it is not symmetric it wont change any of the results, therefore any arbitrary convention works, so we pick the easiest one.

Regardless you still cant actually measure it one way, if you do so conventionally you wont account for time dilation at all and get an incorrect answer where using the relativity approach you will get a more accurate answer but it will be interently a two-way measure.

@freemo So how do we "prove" relativity is correct?

We are Newtonian people, then this guys comes along and says the speed of light is constant, so we set up an experiment to measure the speed of light (one trip, round trip, doesn't matter). We are Newtonian people, so we have absolute space and absolute time and absolutely no problem synchronizing distant clocks. And we find that the speed of light, in our Newtonian understanding of what it means to measure it, is constant. But that breaks our Newtonian understanding! We thus find a contradiction between theory and experiment even though the experiment was interpreted within the theory. What now?

The guy then comes and says: I told you so. The speed of light is constant, and here's how you should think about space and time from now on.

Someone says: but the way you set up the understanding of space and time makes it impossible for the speed of light to be *measured* to be any different!

The guys replies: Exactly my point!

People: Hmm...

@3ammo The problem here is if you pretend we are newtonian people (which we are not since the world is relative and not newtonian) any attempt you make to measure the speed of light accurately will give contradicting and failed results, in part because you assume there is no problem synchronizing clocks when in reality there is.

If i just assume a newtonian world, sync up two clocks at rest then transport the receiving clock to a distance location, measure the speed of light, then bring the clock back and compare I will get one measure for speed of light. If i do the same experiment but this time the transmitting clock is the one physically moved I get an entierly different measurement for the speed of light. Since we are pretending the world is newtonian it essentially shows us little more than "it is impossible to measure the speed of light (using newtonian physics), you will get different values when irrelevant aspects of the experiment change!".

In short because relativity is more true than newtonian physics it is only using relativity you can measure speed of light at all (albeit it 2-way speed of light), and newtonian physics makes it impossible to accurately measure the speed of light at all.

@freemo I'm really fine with that, I keep telling you

@freemo Because then everything is a convention, if we do it your way. Which is fine by me, all theories, in the end, *are* conventions.

Any theory and any framework is a set of choices, these are postulate. You say that calling it a "postulate" says something about the true nature of things, or reality, but it doesn't. As long as you have a consistent set of postulates that can describe measurements, you have a working model of reality. But you can also have a different set of postulates that describe the same measurements. In that sense, all postulates are conventions. I prefer to keep the word "convention" for details within a theory, not its building blocks.

@freemo But the general constancy in the speed of light is about more than making the math easier. As we discussed earlier here: https://qoto.org/@3ammo/105963064680177147, the "isotropy" of the speed of light is also directly related to our notions of space symmetry (among other things). This a statement about the world.

On the other hand, I'm not sure how will gravity look like then, since the theory we use relies on spacetime being a 4D-space, that assertion needs Lorentz transformation to be the same everywhere in all directions (constant c). Again, if you wanna call all of that "just making the math easier", I can also agree because I'm fine with the idea, fundamentally, theories are choices of the way to see the world. But I'm assuming that you don't want that.

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@freemo I agree with both points, but you’re replying to things I’m not saying.

Maybe I’m not clear. I’m not referring to the cosmological principle, nor am I saying the symmetry (short for homogeneity and isotropy) of space relies on the constancy of c.

What I am saying is this: Given free space and no interaction between the observer and the light prior to the detection (both are reasonable assumptions), why would light behave differently moving towards an observer than away from them? A statement of this sort says something about the asymmetry of free space. Why? Because this is not really about light or sound or similar things, it’s about establishing a way to measure things in general, we must send signals to interact with distant objects. If light was like sound, the postulate would be “the speed of signaling is constant everywhere”.

Why do we want space symmetry? Like I said, this is NOT about the cosmological principle and our large scale observations. It about our *assertion* that there must be a “reason” to differentiate one point or one direction in space from another. If that was not the case, then science (or even any communication) wouldn’t exist because simply being in a different place means there are different “laws” of physics, Of course, it’s not even a law of it changes every time we move.

And the above paragraph is NOT about the measurement of the round-trip of light that will remain the same. You can’t even make that statement, let alone make a measurement, if the laws are different in each point in space without *reason*. So what is the reason? It’s any space dependent interaction. We start with completely symmetric clean slate, then add non-symmetric objects as space-dependent Lagrangian or whatever you choose to represent physics. It’s the first law of Newton “Things are the same (symmetric) unless there is a reason (force)”. Now, if you assert that light has different speeds in different directions (keeping round-trip measurements constant), then you have provide a reason, that is, some interaction theory. Fine, in THAT theory, you will have to assert the existence of a signal that propagates with symmetric speed: what we call light.

Locality is another reason we have all this, in addition to the symmetry of space.

You see, this is not really about light or measurements. You can’t measure anything without having a framework for interpreting such measurement. This is really deeper than just accounting for the constancy of the round-trip speed of light.

π Dr. Freemo π³π±@freemo@qoto.org@3ammo My point is you can literally make up any theory no matter how nonsensical and so long as that theory only has the result of effecting the one way value of c you can not disprove it no more than you can prove c to be symetrical.

I could for example say “Well space just happens to be asymetric by its very nature, there is in fact a special orientation and space itself is deformed in such a way to give these results” If i say that it wouldnt disagree with any evidence we have and is just as plausible as saying space-time is inherently symetric.

take a step back and look at the already existing asymmetry we see in special relativity. If i am on a ship moving away from some other ship, I will always see the clock on the other ship move more slowly than mine. This is true no matter which ship did the accelerating that caused the movement. So from my perspective on the ship it would appear (incorrectly) as if i am in a special frame of reference and/or that there is some prefered orientation to the ship. But we also know the same would be viewed from any other frame of reference and that round-trip the symmetries resolve and we only have a one-way paradox (not unlike our current discussion). The difference is in this case we can actually see an asymmetry, in the case of light that is hidden from us. Its only because the asymmetry resolves itself on round trip that we consider the paradox solved, because it effectively produces consistent results that can be tested.

So why does one asymmetry bother you anymore than the other? There is no framework to suggest to you light has symmetry anymore than there is a framework to tell you it is asymmetric.. so you have no reason to prefer symmetry