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.


Maybe because the only way we (part of the universe) can understand anything is by breaking it into smaller parts and study the relations between them? It's always the relation that we call "law". And relations need at least two parts. Maybe?

@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 My point is not to pretend that the world is Newtonian, I simply meant our state of knowledge, our working theory was Newtonian. I was answering the question of "How do we prove relativity to be correct in the first place?" And that is by finding a contradiction between the Newtonian view and the measurements made within the Newtonian view.

@3ammo sure.. which means the fact that you think you can measure light one way in the newtonian view, and it turns out you cant (without getting contradictory results) only proves the original assertion, that is, that light can only be measured round-trip and it is fundementally impossible to measure one-way speed of light.

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

@3ammo I know, just saying because im not sure it makes what you say relevant to the topic if we both agree what I said to be true.. my two assertions are threfore valid.. 1) you can only measure light 2-way 2) the speed of light being instantaneously constant is a convention and not an assertion as to how it is in real life.

@freemo Yeah I'm writing the other reply. I think we actually agree in a certain sense. You want to call it a "convention" because of your view of reality as you explained it, I want to call it a "postulate" because of the way I see theory and reality. It's a philosophy discussion at this point (this is not meant to be disparaging).

@3ammo I'm not sure if its a philosophy difference so much as a definition one.. though if we agree on most of what I said its hard for me to see how your perspective is different at all. You want to call it a postulate, but if your definition of postulate is the same as mine im not sure how if we agree on everything else.

@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.

@3ammo well no if we do it my way conventions are things we just do to make the math easier but doesnt reflect reality in any way, like "conventional current" in electronics... postulates are assumptions made with or without evidence, about how the world works and used to derrive equations based on that assumption... axioms are assertions of any type assumed to be true... so a postulate and a convention would be the two types of axioms.

@freemo But the general constancy in the speed of light is about more than making the math easier. As we discussed earlier here: qoto.org/@3ammo/10596306468017, 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.


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.

two problems with this.

  1. space symmetry holds true for many things, but none of them in any way rely on a symmetry of speed of light. If light is antisymmetric then space can still be isotropic in all the ways we have observed it to be. you are referring to the cosmological principle and all it states is “When viewed at a large enough scale the universe will look the same to all observers”… this principle holds true even if c is asymmetric.

  2. we never defined how c is asymmetric, nor did I state it is just some arbitrary direction in space, the asymmetry could arise through all sorts of rules (none of which is testable mind you). For example it could be that light travels faster in the direction you are moving than the opposite. In relativity fashion therefore the direction of the asymmetry is opposite for each of the observers in a clock synchronization experiment, yet due to the reasons mentioned before once this is resolved by a full round trip to compare clocks the asymmetry cancels out and you get what looks like symmetric results. In fact this example is very much in line with what we see with time dilation and special relativity how the act of making a round trip resolves the twin paradox as the acceleration to reverse direction resolves the paradox.

The point your missing (I think) and that is so important to this is that if an asymmetry exists it can not be distinguished from a symmetry in part to the impossibility of measuring light one-way. It is of a similar nature as trying to know two complimentary properties in QM, not only is it impossible, that impossibility is fundamental.


@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.

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@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

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