The Speed of Light


(Dr. Patrick Trischitta) #21

(Robert Byers) #22

Yes they go on about this a great deal. I strongly suspect the slit experiment is wrong in its presumptions of how matter/light works. i didn’t bring it up. They make crazy claims about things based on this experiment.
i’m still entry level on this speed of light claims etc etc.
Maybe posters here can give better answrs then wiki or the youtube.

(Ashwin S) #23

Anther thing that travels at the sped of light are gravitational waves (if they exist)…

Basically what Einsteins seems to have done is define the universe in terms of 4 Dimensions instead of three. He equated the fourth dimension with time.
The way i understand it is that the 3D world is moving along the fourth Dimension at a speed. I guess it would be impossible to observe anything that moves faster than the world for anyone one who is in it, hence the maximum speed possible in the universe is the speed at which the universe is moving along the 4th axis… this speed is identified with the speed of light.
@dga471 and other physicists can correct me if I totally botched it up…

Edit: This is where relativity becomes important. For example, if we are travelling in a car. From the POV of those in the car, it’s as if everyone is at rest. However from the POV of those outside, the car is moving at speed X. So the 3D space is like a car moving along time.

(Robert Byers) #24

I never heard that before. Another poster said it was a spectrum!? I guess my entry level point is whether this “light” is the only thing going that fast? Is it only when both are combined?
of coarse I’m suspecting the electro and the magnetic elements in combination are just provoking OUT the light within the essence of the universe.

(Robert Byers) #25

Thats interesting. YES einstein insisted light was the fastest moving thing.
These two components gets my attention. That means only in combination do they become light and the speed of light.
i agree they would be/have a source. yet its still a option they only poke out light.
Then you say gravitational waves, i thought i heard of others, go as fast as speed of light. THEN why not call it the speed of gravitational waves which only includes Electro/mag /light wave??
I’m hinting here at a option that these electro/mag and gravitational waves, if so( as you say), are all just poking out the light from a universal essence or ether.
in fact i understand maxwell was impressed by the same speed for the two components and that led hin to his conclusion that light was a electromagnetic wave. yet if gravtational waves go the same speed then that undercuts his hypothesis as i see it.

(Daniel Ang) #26

I don’t normally think of Special Relativity in this way…the speed of light is just that, an axiom that we take to be true (and have found to be true). It doesn’t make much sense to me to say that the 3D world is moving along time at the speed of light. Like what does that even mean? A speed has units of length per time, so you can’t move along time at some “speed”. Or maybe I’m misunderstanding you.

(Daniel Ang) #27

Just to clarify, as you probably know, you can “move” faster or slower in time compared to some observer by moving faster or slower relative to that observer. The way I visualize this is that the “combined speed” in which you move in 4D spacetime has to be constant, due to the speed of light always being constant in all reference frames. Perhaps something like this that is what you are trying to say.

(S. Joshua Swamidass) #28

I think @PdotdQ put a formulation of relativity out there that sounded something like this.

(Ashwin S) #29

Its mainly how i visualize the idea. Some of it is from how mathematicians derive a basic 4D space such as tesseract (which is a cube moving in the 4rth dimension).

I see it as a more physical thing (and i know that’s not how SR explains it. It just assumes that the speed of light cannot be broken as an axiom.). i visualise that its impossible to go above light speed because Space is moving along time at that speed… so there is probably a payoff in terms of energy… inertia increases as any object tries to break this boundary…etc.
I have no idea if there is a scientific framework in which this visualisation fits in.

(Daniel Ang) #30

So I found this:

which is basically similar to what I said

So maybe I was taking @Ashwin_s too literally. :sweat_smile: He is sort of right, I guess.

(Ashwin S) #31

Its definitely an intriguing question… the obvious question is whether the time mentioned in speed (i.e as measured in seconds from a particular vantage point) is the same as the dimension of spacetime. Since there is no “Absolute” measure of time in SR, this seems unlikely (atleast to me).

All things said and done, anyway to visualise this is bound to have errors.


I agree with @dga471; this is a correct statement.

If you are talking how spacetime is continuously being build up by a succession of spaces evolving over time (as in the growing block Universe picture), this is not how the cosmic speed limit is obtained in relativity.

There are two speeds commonly used in relativity, the proper velocity and the coordinate velocity. The time in proper velocity refers to the proper time of the object, while the time in the coordinate velocity refers to the time measured in the particular coordinate system. The coordinate speed of light is not always c, and indeed can be 0.

(Robert Byers) #33

If I understand. If thats true then its saying LIGHT just uses this speed . This suggests that light is trapped in this speed limit.
WELL that could mean its only the source/provocation that ignites light THT IS TRAPPED. Yet light is everywhere all the time. So no speed of light exists.
this would help in explaining star light claims of a old universe. instead light was instant at creation and later there was a interference ofa speed cop who slowed everything down. So light aLSO now can only go that fast.
Yet its not actual light but a poking of light . Its the speed of poking or the ripple in the pond.

(Daniel Ang) #34

Why do you think light is everywhere all the time? If I turn off the light in your room, it will go dark. There would be no more light. That seems to disprove the statement that light is everywhere all the time.

(Jacob) #35

Unfortunately it is the dogma of some churches that the universe is at the most only a few thousand years old. If you ask them they will tell you that far from being some secondary thing, it is important and “the Gospel stands or falls on it.”

From there light “has” to be instantaneous or everywhere all at once, otherwise there is the distant starlight problem (I forget how YEC explains away the redshift). YEC has to explain away even the most well-known facts that get in the way of ideology.

This thread was a nice mini-course in electromagnetism, with a bit of Relativity thrown in.

(Retired Professor & Minister.) #36

Robert, I’m curious why you say that “light is everywhere all the time” and “no speed of light exists”? Genesis 1 says that God divided the light from the darkness (Genesis 1:4) and darkness is the absence of light. As to the speed of light, I’ve actually observed first-hand an experiment which measured the speed of light. So I know that it exists.

Of course, if one leaves behind the usual definition of light which most people use (i.e., the visible spectrum which our human eyes are capable of seeing), and one applies the word to all electromagnetic radiation, then I may see [no pun intended] what you are saying about light being everywhere. Electromagnetic waves are everywhere because all matter that is above absolute zero (0 Kelvin) is radiating electromagnetic radiation. Indeed, the discovery of the cosmic microwave background radiation was a very big deal.

I can still remember the news coverage of this. The discovery was basically an accident when engineers at Bell Labs were very frustrated as they tried to get rid of a “hum” of interference afflicting their new type of horn-shaped antenna. No matter what they did, they measured that interference coming from every direction of the sky.

@dga471 no doubt knows far more about this discovery than I do. But if I recall, this frustrating day for a pair of Bell Lab engineers soon came to be considered an important confirmation of the Big Bang Theory. That’s what I remember the general media reporting at the time. (Of course, I learned long ago to take everything the mass media says about science with a grain of salt, and thus my question.)

(Robert Byers) #37

Its from the bible. Genesis. It means God created light everywhere on day one. That same day he divided light, in order to create time, from the darkness. so light is hidden by the darkness. one must poke it out.
So our souyrces of light, stars, sun, fire, are just poking light out. Not creating light.
This is what the author of genesis implies.
Si i’m suggesting we are living in a modern error that light comes from a source, thus has a speed, and so indeed computing timelines from starlight are false.

(Robert Byers) #38

Any experiment would just be measuring a provocation of light. Its not proven your watching the speed of light.
Just a source of light which could be just poking light out of the essence of the universe.
genesis says god created light. Then divided from darkness, to create time, and thus everywhere is dark but with light hidden behind it. Its poked out. tHe speed of this is not light, as liught is everywhere at once, but only the explosion of light at a point.
its speculative but starting from genesis and watching explanations on light i think its likely there is no speed to light . it would fix that crazy slit experiment possibly.

(Daniel Ang) #39

I don’t see in my Bible where God is “poking light out” from the darkness. Can you show me where that word is used?

Also, Genesis says that God is the one who divides light from darkness. Not light sources. Light sources can create light (or more accurately: they can convert energy into light), but they cannot divide light from darkness in the same way that God did. You aren’t suggesting that God is just a giant light source like your room lamp, right?

(S. Joshua Swamidass) #40

Would you like to hear about the first experiments in which the speed of light was measured? They are pretty amazing…