How does light propagate? By what means does light get from Point A To Point B?

Kryptid · « **Reply #80 on:** 02/05/2024 20:03:22 »

Quote from: hamdani yusuf on 30/04/2024 22:18:20

The required characteristics of a standard is consistency from time to time. Its value in the past should be the same as its value in the future.

As far as I am aware, there has been no good evidence to date that the speed of light in a vacuum has changed over the lifespan of the Universe. All that has changed is the precision with which we have measured it.

hamdani yusuf · « **Reply #81 on:** 03/05/2024 08:14:34 »

Quote from: Kryptid on 02/05/2024 20:03:22

Quote from: hamdani yusuf on 30/04/2024 22:18:20
The required characteristics of a standard is consistency from time to time. Its value in the past should be the same as its value in the future.

As far as I am aware, there has been no good evidence to date that the speed of light in a vacuum has changed over the lifespan of the Universe. All that has changed is the precision with which we have measured it.

Perhaps it's because the speed of light is defined to be a constant, and spacetime is defined so that its expansion doesn't change the speed of light.

alancalverd · « **Reply #82 on:** 03/05/2024 09:09:15 »

Quote from: hamdani yusuf on 02/05/2024 15:14:04

Even making good standards is just an instrumental goal, serving to help achieving the common terminal goals among the users of the standards.

In the case of public water supply, there are two quite different terminal goals: profit and sterility. EU rules, as implemented by the UK government, dismissed the second.

Kryptid · « **Reply #83 on:** 03/05/2024 17:56:57 »

Quote from: hamdani yusuf on 03/05/2024 08:14:34

Perhaps it's because the speed of light is defined to be a constant, and spacetime is defined so that its expansion doesn't change the speed of light.

Not so. If the speed of light had changed over the course of the Universe's history, we would be able to see differences in the behavior of distant galaxies and stars compared to closer galaxies and stars.

hamdani yusuf · « **Reply #84 on:** 04/05/2024 00:21:32 »

Quote from: Kryptid on 03/05/2024 17:56:57

Not so. If the speed of light had changed over the course of the Universe's history, we would be able to see differences in the behavior of distant galaxies and stars compared to closer galaxies and stars.

Aren't they red shifted?

alancalverd · « **Reply #85 on:** 04/05/2024 11:04:49 »

Irrelevant. Redshift has nothing to do with variation of c.

hamdani yusuf · « **Reply #86 on:** 08/05/2024 13:53:16 »

Quote from: alancalverd on 04/05/2024 11:04:49

Irrelevant. Redshift has nothing to do with variation of c.

c=λ.f
Redshift reduces frequency. For c to be constant, wavelength must increase accordingly. Wavenumber must decrease accordingly.

Quote

The radius of the observable universe is estimated to be about 46.5 billion light-years.
Age 13.787+/-0.020 billion years

https://en.wikipedia.org/wiki/Observable_universe

If c is constant, wouldn't the edge of observable universe be invisible?

alancalverd · « **Reply #87 on:** 08/05/2024 17:51:57 »

Quote from: hamdani yusuf on 08/05/2024 13:53:16

c=λ.f
Redshift reduces frequency. For c to be constant, wavelength must increase accordingly. Wavenumber must decrease accordingly.

As observed.

hamdani yusuf · « **Reply #88 on:** 09/05/2024 10:26:36 »

Quote from: alancalverd on 08/05/2024 17:51:57

Quote from: hamdani yusuf on 08/05/2024 13:53:16
c=λ.f
Redshift reduces frequency. For c to be constant, wavelength must increase accordingly. Wavenumber must decrease accordingly.
As observed.

Quote from: hamdani yusuf on 08/05/2024 13:53:16

If c is constant, wouldn't the edge of observable universe be invisible?

Kryptid · « **Reply #89 on:** 09/05/2024 17:09:45 »

Quote from: hamdani yusuf on 08/05/2024 13:53:16

If c is constant, wouldn't the edge of observable universe be invisible?

It basically is.

hamdani yusuf · « **Reply #90 on:** 21/05/2024 12:19:18 »

Quote from: Kryptid on 09/05/2024 17:09:45

Quote from: hamdani yusuf on 08/05/2024 13:53:16
If c is constant, wouldn't the edge of observable universe be invisible?

It basically is.

So what's the furthest observed universe now, if its not the edge?

alancalverd · « **Reply #91 on:** 21/05/2024 14:38:29 »

By definition, the furthest bit you can see is the edge of the observable universe! Currently it's about 13.5 billion light years away.

hamdani yusuf · « **Reply #92 on:** 27/05/2024 08:22:46 »

Quote from: alancalverd on 21/05/2024 14:38:29

By definition, the furthest bit you can see is the edge of the observable universe! Currently it's about 13.5 billion light years away.

https://en.m.wikipedia.org/wiki/Observable_universe
This article says that observable universe is 93 billion light years in diameter.

alancalverd · « **Reply #93 on:** 27/05/2024 08:57:28 »

I think you have left out a factor of 1 000 000 000 somewhere. The Green Party needs you!

hamdani yusuf · « **Reply #94 on:** 28/05/2024 04:37:02 »

Quote from: alancalverd on 27/05/2024 08:57:28

I think you have left out a factor of 1 000 000 000 somewhere. The Green Party needs you!

I think it's a type which has higher probability when editing in a mobile phone. Thanks for the correction.

alancalverd · « **Reply #95 on:** 28/05/2024 17:44:12 »

Respect for doing this stuff on a phone!

hamdani yusuf · « **Reply #96 on:** 05/07/2024 22:05:42 »

Knowing the one-way speed of light

Quote

So you think you have a brilliant idea about how to measure the one-way speed of light, only to discover that it contains a very trivial oversight. Luckily this initial failure was the start of a few new insights on the relationship between one-and two-way speed of light. Well, at least new to me...

What do you think: is there a way that the one-way speed of light is not identical to the two-way speed of light?

Content:
0:00 Introduction
0:30 Origin of the two-way speed of light definition
1:40 The Fizeau speed of light experiment
3:27 Trying to measure the one way speed of light (and fail)
12:07 Speed of light from the wave perspective
18:24 Problems related to opposing anisotropy in vacuum
21:23 Violation conservation laws (abstract)
22:23 But... when spatial anisotropy changes with time...

alancalverd · « **Reply #97 on:** 05/07/2024 22:40:50 »

Suppose one made a "double Fizeau" apparatus, with two toothed wheels on a longish single axle. A light beam from source S is chopped by the first wheel A then passes through the second wheel B and is detected at receiver R. At zero rotation speed, R detects a maximum intensity. Now drive the wheels with a smaller cog situated in the middle of the axle (so that they accelerate equally). The signal at R decreases, then increases to a second maximum at some particular speed of rotation. This tells us how long it took the light to travel from A to B - no reflection is involved.

What is the "trivial oversight"?

hamdani yusuf · « **Reply #98 on:** 06/07/2024 01:37:27 »

Microwave Standing Waves

I think the formation of standing wave can show if the speed of light in one direction were different from the opposite direction.

https://www.wolframalpha.com/input?i=plot+%28sin%28x%29+%2B+i+sin%281.5+x%29+%29

https://www.wolframalpha.com/input?i=plot+abs%28sin%28x%29+%2B+i+sin%281.5+x%29+%29+

hamdani yusuf · « **Reply #99 on:** 06/07/2024 02:29:13 »

Quote from: alancalverd on 05/07/2024 22:40:50

Suppose one made a "double Fizeau" apparatus, with two toothed wheels on a longish single axle. A light beam from source S is chopped by the first wheel A then passes through the second wheel B and is detected at receiver R. At zero rotation speed, R detects a maximum intensity. Now drive the wheels with a smaller cog situated in the middle of the axle (so that they accelerate equally). The signal at R decreases, then increases to a second maximum at some particular speed of rotation. This tells us how long it took the light to travel from A to B - no reflection is involved.

What is the "trivial oversight"?

The long axle may be easier said than built. Trading off its length and rotation speed to produce unambiguous results might be a problem.