One and Two Way Speed of Light

Given the types of modification to the directional speed of gravity in this discussion:

No, there is no observable consequences for orbital mechanics at least up to order ~1/c^2 (or at least we don’t yet know of an experiment that can test it).

The reason is this: up to order ~1/c^2, gravity is exactly equal to electromagnetism (modulo a negative sign in the Lenz’s Law). Thus, if there is no experiment that can detect the one-way speed of light, there is no experiment that can detect the one way speed of gravitons up to this order.

I don’t know the answer for the full theory of gravity. But most orbital motion are order ~1/c^2 or lower (typically much lower).

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I don’t understand this. If we have two objects orbiting each other, the object at one end, let’s call it A, sends out its attraction at infinite speed to the object at the other end, call it B, while B sends its attraction at c/2. So A is attracted to where B was a while ago, while B is attracted to where A is right now. That seems quite different from both being attracted to where the other was half a while ago. But perhaps it all works out.

Actually, A is not attracted to where B was a while ago, but where B is now (if B is moving with ~constant velocity). This non-intuitive result comes from the fact that the gravitational potential has to be evaluated at retarded time where c is now c/2.

This is the same case as in electromagnetism. You can read more about it here.

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I do not understand what either of those articles mean.

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In broad strokes: in the case of when the speed of gravity is finite,

This has to be satisfied for relativity to not be violated. The point is that the situation is not as one would intuitively think:

Sorry, replied on the wrong thread…

It seems the physicist’s replies are in and Patrick’s claim is refuted.

The error here is the ‘finite and equal to c’ claim. That gravitational waves and light travel at the same speed is a stunning revelation, but unless there is a synchronised clock at the source it doesn’t tell us anything about the one-way speed.

And this one also:

He actually calls his model the ASC (Anisotropic Synchrony Convention) and it makes no claims about an expanding universe (although Lisle does agree). It is a convention and as such can’t be falsified when compared with the ESC.

Special thanks to the @physicists for their contribution.

@physicists, is this correct? Does the YEC idea that light travels instantaneously in one direction actually plausible?

And does it require that there be special locations, i.e. that the earth is special — light moving toward the earth travels instantly while light moving away from the earth travels at c/2? How does one decide which locations are special in any pair of locations?

Light and gravitational waves occurred 1.7 seconds of one another and then traveled 130 million years in all directions to detectors on Earth. Gravitational waves and lightwaves traveled together at a finite speed c.

First of, this is not a YEC idea. The ASC was known long before Leslie did anything with it. Yes, it is actually plausible. However, the question is whether it actually resolve YEC’s problems.

  1. If according to YECs, the bible is the literal word of God, why does God wrote the bible using the non-intuitive ASC? Is the YEC God trying to deceive people?
  2. There are many other problems with YEC besides the distance starlight problem.

That is indeed a way to get a different one-way speed of light than its two way values - and I imagine that YECs won’t have any problems with the Earth being special. However, it is not necessary, and glancing at Lisle’s paper it does not seem that he assumed this.

Instead, he assumed that for every observer light going away from them and towards them possess different speeds. Is this allowed by relativity? Yes. Is this ad-hoc and entirely unnecessary unless one really wants to stick to the literal interpretation of the bible? Also yes.

As was stated multiple times in this thread, no one is debating this. The statement published by the LIGO collaboration and co is on the two-way speed of light and gravity. The question is whether the the two-way speed of light and gravity is different from the one-way speed of light and gravity. I suppose this statement

is the one in question, as we cannot actually confirm it.

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This is similar (and more clever in certain ways, as it is consistent with existing physics) to the general YEC view that God created everything with the appearance of age. Now, YEC has gotten a worse reputation because of past history and the fact that there is tons of other evidence that the Earth is old, but it is likely that this is also how outsiders view our (non-YEC) attempts to harmonize the biblical Adam and Eve with evolutionary biology. Namely, it is allowed by the science, but it is scientifically unnecessary and “inelegant”. That might also explain the negative reaction of some hardcore TEs to the GA proposal. (Even though I grant that the GA proposal doesn’t reinterpret biology in anywhere nearly the same extent that Lisle’s proposal reinterprets physics.)

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Maybe non-intuitive post-Einstein, but there are many examples of counter-intuitive behaviour that we know to be true (you gave one on this very thread). If the universe doesn’t conform to our expectations is that God trying to deceive people? I don’t think so.

This is not the case of the universe not conforming to our expectations. As you said, ASC is just a convention.This the case where the author of the bible can choose to use any other conventions but decide to choose an odd convention when writing the bible. This is equivalent to: if in the bible it was said Jesus had 12 disciples, the author is actually using base-4 numbers.

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This makes me think about debates over the tremendously large numbers of Israelites described as participating in the Exodus in the Bible, and the argument that they must have been written in a different basis. But the argument that they usually raise is that that would have been the cultural convention at the time. Thus, if someone wants to argue we should adopt ASC instead when reading the Bible, they better have a good textual and/or cultural argument for it. Otherwise it seems like a blatant act of eisegesis - that we’re adopting that convention solely because of extra-Biblical, scientific evidence. This is an example where I am puzzled by how YECs want to view Scripture.

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How would that work? If we have two observers, A and B, doesn’t that mean that a given photon passing between them travels at two different speeds at the same time? And is it possible for those two speeds to be infinite and c/2?

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Yeah, that is a good way to put it. If YECs really believe that the bible writes using ASC, they need to have a good argument for it. I presume that the author wanting to trick their readers is not something YECs will abide by.

I didn’t care to read Lisle’s paper closely, so I don’t know how it works in his theory. However, In the theory with an anisotropic one-way speed of light that I am more familiar with, the one-way speed of light is only anisotropic in a moving frame. If A and B are moving with respect to each other, they are in a different frame and thus it is okay for them to measure different one-way speeds of light.

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How would they measure one-way speeds? I thought there was no way to do that. I also thought that under relativity the measured speed of light was invariant. Very confusing.

Sorry, I shouldn’t say “measure”. It’s that the photons passing from A to B can have infinite one-way speed as considered by frame A or finite one-way speed as considered by frame B. I am just trying to answer your question:

Also,

The two-way speed of light is invariant, not the one-way speed of light.

Could those same photons equally be considered to have infinite one-way speed in frame B and finite one-way speed in frame A. Or could they equally be considered to have equal speed in both frames? Are there any constraints on what observers in either frame could consider, jointly or separately?

Until modern times ASC was not an odd convention, it was the standard. Ancient astronomers recorded the time they saw an event but knowing neither the distance or speed of light, they obviously didn’t deduct any light travel time.