downvoted because time traveling through a medium vs traveling through curved space are not anywhere near the same underlying principles[0].
The implication being suggested is - if I was trapped in a block of plastic or... underwater, I would experience time different compared to someone standing on land just because "c" is slower.
Clearly not the case.
To be specific, when "the speed of light" is discussed like this, it usually means the "speed of causality"[1] which is the underlying meaning of "c" in relativity.
The speed of causality through a medium (i.e. water) is the same as a vacuum if spacetime curvature is the same.
Upvoted you and thanks. I was hoping someone would mention "the speed of causality", because to my layman's mind, I've always found thinking about "the speed of causality" makes vastly more sense of the universe to me and makes spacetime/relativity/and-all-that-jazz far easier concepts to comprehend.
For example, if a powerful laser beam was shot off in a vacuum towards an observer who is far away, it's not the "speed of light in a vacuum" which dictates the time at which the observer detects that laser light, it's the speed of causality in that volume of spacetime which determines when that light beam reaches them/is detected.
Space is a medium of variable density that impacts the speed of light and everything else. That is clear with regard to solar winds and termination shock.
The curvature of space is directly related to time travel. Strange how you completely ignored that much larger portion of my comment to punch a straw man.
> is the same as a vacuum if spacetime curvature is the same.
If that were true particle physics wouldn’t need dark matter/energy to balance conditions that are irregular upon observable matter alone.
Causality, at least in physics, is an abstract notion and not an empirical notion. In causality effects occur in the same order as their respective causes which is substantive for logical consider, but is not necessarily measurably accurate or expected.
While there are a lot of big words being used, there appears to be a gap in understanding the core principles related to the article.
> If that were true particle physics wouldn’t need dark matter/energy to balance conditions that are irregular upon observable matter alone.
You responded to my vacuum statement as if we agree the vacuum is perfectly empty. In relativity, the vacuum is not considered empty[0]. Maybe I should have used "patch of space", but more importantly I said "if the spacetime curvature is the same". That literally defines how causality moves through it so that would be inclusive whatever was there including dark matter/energy, which brings us to...
> Causality, at least in physics, is an abstract notion and not an empirical notion... but is not necessarily measurably accurate or expected.
No it's not... From the wiki you quoted: "In Einstein's theory of special relativity, causality means that an effect can not occur from a cause that is not in the back (past) light cone of that event. Similarly, a cause cannot have an effect outside its front (future) light cone."
We're talking about relativity here, not philosophy or another topic where causality isn't well defined. It is not abstract. It is explicitly defined as "c" in Einstein's equations. I'm not sure what you're trying to prove/disprove here.
You can say I attacked a straw man, but the original comment was edited. So now, I don't know.
I recommend PBS SpaceTime[1] - I still don't understand a lot of things in this space even after watching many videos multiple times, but it really helped put pieces together.
There were no big words or any form of exotic vocabulary.
> No it's not
Causality states that the order of effects must match the order of events. The Wikipedia articles states that almost verbatim. The mention of a light cone binds the general use of the word to its application of physics without changing the definition. No where does the article extend that definition to anything vaguely measurable.
> You can say I attacked a straw man, but the original comment was edited.
It was most likely edited hours before your reply. When I completed the edit there were no replies. I am living on the otherside of the world from the US in a far away timezone.
> No where does the article extend that definition to anything vaguely measurable.
Ah, you're right, I didn't realize you dropped the "speed of" in the "speed of causality" (because the "speed of causality" can be measured and expected... what does "expected" even mean in this context?!). So going 2 replies up you linked to Causality and made a statement about causality but ignored the "speed of causality". So nothing was said?
So you agree with me!
> It was most likely edited hours before your reply. When I completed the edit there were no replies.
Ah! Don't worry, thankfully we know that I replied to you 35 minutes later thanks to Hackernew's API[0][1] and that I'm half a world closer in SGT, and that I was originally replying to something that was edited away.
The implication being suggested is - if I was trapped in a block of plastic or... underwater, I would experience time different compared to someone standing on land just because "c" is slower.
Clearly not the case.
To be specific, when "the speed of light" is discussed like this, it usually means the "speed of causality"[1] which is the underlying meaning of "c" in relativity.
The speed of causality through a medium (i.e. water) is the same as a vacuum if spacetime curvature is the same.
[0] https://www.youtube.com/watch?v=CiHN0ZWE5bk
[1] https://www.youtube.com/watch?v=msVuCEs8Ydo