# Why must the speed light be constant?

Discussion in 'Physics & Math' started by Saint, May 30, 2021.

1. ### Write4UValued Senior Member

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OK those are all results, not the cause of the phenomenon.

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5. ### SaintValued Senior Member

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Then why the speed of light is constant in any frame of reference?
It is constant to a person standing still, also constant to a person sitting on a moving train.
Why?

7. ### SaintValued Senior Member

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Does gravitational wave travel at the speed of light?

8. ### exchemistValued Senior Member

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As I understand it, Maxwell's equations, at the time they were devised, predicted that the speed of light, as measured "at rest" in the vacuum - whatever that signifies - would be independent of the motion of the source.

That naturally led to questions about what "at rest with respect to the vacuum" - which is nothingness - could possibly mean. Hence we got the ideas of the "aether" and the arguments that led to Michelson and Morley's experiment, which helped to settle the matter by providing results that were consistent with there not being any such aether - or preferred frame of reference - in the vacuum.

So in the end it was experiment that showed the independence of c from any frame of reference, a finding that was in fact consistent with Maxwell's earlier work, though people had not realised it at the time.

9. ### arfa branecall me arfValued Senior Member

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Well, that doesn't actually scan all that well.

The technology is possible (even if we never invented it) because the speed of light is constant; ergo transmission of light signals can be precisely timed.

If you want to know what caused/causes light to have a constant speed, you probably need to look more closely at the beginning of the universe.
But right now, it causes us to consider that information can be reliably transmitted (thanks, universe!).

10. ### Write4UValued Senior Member

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Exactly, I can understand what causes limits in a medium. It can be clearly demonstrated. But the sound limit can be broken, which raises the question if light limit can be broken and what happens to the offending object.

AFAIK, there is a hypothesis that "virtual particles" must travel at FTL which makes them unobservable, unless they stray below "c" and immediately interact, break down, or return back to the FTL dimension? This phenomenon was observed when the Higgs boson was made manifest and which immediately disintegrated into 2 muons.
https://home.cern/news/press-releas...ce-first-indications-rare-higgs-boson-process

This event was almost instantaneous.
https://en.wikipedia.org/wiki/Higgs_mechanism
Yes, there is something that gives spacetime its constancy, but what exactly is that? What imposes a speed limit in vacuo is the question. Temperature? Is in vacuo space denser at absolute zero?
Might that even explain an original dense "singularity"?
I have always viewed the "inflationary epoch" as the unrestricted expansion of spacetime into an a priori timeless "permittive condition", which must have existed before the BB. Else the BB itself would not have been possible. And would explain the initial FTL expansion of the universe for that instant.

Perhaps this may have been driven by an unimaginable amount of energy being released in the same place, at the same time (Chaos). Once spacetime cooled, the restrictive laws of spacetime as we know them took hold and started regulating all events occurring at or below "c" thereafter?

Even if the BB event itself is outside our ability to measure, the chronology of post-BB universal evolution should give us a glimpse of its causality.

Last edited: Jun 1, 2021
11. ### SaintValued Senior Member

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If I travel at 0.5c speed, when I measure the speed of light in the same direction, it is also 1.0c ?
if speed of light is constant, why when we see the light of stars far away, there is red shift?

12. ### exchemistValued Senior Member

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Because of the cosmological red shift. Space has expanded since the light was emitted, thereby stretching out the length of the waves.

13. ### PintsizeRegistered Member

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Does lighting a Candle mean sparking then holding the flame to the Wick?

14. ### exchemistValued Senior Member

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What has that to do with the thread topic?

15. ### SaintValued Senior Member

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Redshift is due to change in frequency, not the speed of light, I have been confused.

16. ### SsssssssRegistered Senior Member

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The invariance of the speed of light is an assumption. There is no answer to "why" until we get a new theory. We accept it as true because special relativity is derived from that assumption and it works. That's all the justification there ever is in science for its basic assumptions.

17. ### Write4UValued Senior Member

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I believe the term for a self-evident phenomenon is "axiom" .

ax·i·om
noun
a statement or proposition which is regarded as being established, accepted, or self-evidently true.
1. "the axiom that supply equals demand"
MATHEMATICS
a statement or proposition on which an abstractly defined structure is based.
2. "the axiom that water is wet"

Last edited: Jun 1, 2021
18. ### exchemistValued Senior Member

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But an assumption based on generalising from observation, isn't it?

19. ### SsssssssRegistered Senior Member

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Kinda. AFAIK we don't know how Einstein came up with the idea but he said he tried to imagine riding a motorcycle alongside a light wave and discovered Maxwell's equations couldn't describe a light wave stationary next to him. He was certainly aware of the Lorentz transforms as a mathematical fix for Maxwell's equations, so he may have discovered that transforming the plane EM wave kept its speed invariant. Then he could take that silly idea and see where it led him I guess. That would be an assumption based on taking a mathematical patch to a theoretical model that was built on observation. So yeah, it's based on observation at a few degrees of separation. He didn't just pull the assumption out of his ass, if that's what you're asking.

To summarise fifty years of futzing around, Lorentz and Maxwell had figured out some implications of an assumption they didn't know they were making. Einstein reverse engineered the assumption out of their ideas and then rebuilt everything from that. That's kinda like summarising WWII as "there was a fight, the Allies won", but you'd need a BIG book to cover it properly.

Last edited: Jun 1, 2021
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20. ### PintsizeRegistered Member

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Ssssssss how large a book?

21. ### Write4UValued Senior Member

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Still no explanation why massless particles, which do not recognize quantum fields in vacuo, still appear to encounter a hard limit @ "c".

22. ### PintsizeRegistered Member

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Dear Write4U,

How can i know how massless particles shall behave in Vacuo at a hard limit?

Should i be told particles WILL do something is that determined?

Is WILL determined?

23. ### Write4UValued Senior Member

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Apparently so. No one has observed any massive or massless particle moving @ FTL.

But the question is somewhat misleading . A particle will not do anything but be a particle, unless acted upon by an external causality.

Virtual particles are suspected of going @ FTL, but they cannot be observed, unless they somehow manifest at "c".

Is it possible that waves in quantum fields move a FTL and that causes a natural barrier @ c.

Limits can be caused by stationary, or slow moving, or fast moving barriers

The Higgs boson was visible but only for an incredibly small instant before it decayed. (see link in post #27)

As to determinism, AFAIK the laws of causality and conservation only allow for a specific effect from a specific causality. Can't make a purse of a sow's ear.....