# The Naked Scientists Forum

### Author Topic: Speed of light always the same  (Read 12410 times)

#### diegostation

• Jr. Member
• Posts: 18
##### Speed of light always the same
« on: 10/05/2005 00:54:56 »
I've heard that it doesn't matter if you have an initial velocity or not when turning on a flashlight, the speed of the light is always 300,000 km per second, how can this be?

#### moth

• Jr. Member
• Posts: 12
##### Re: Speed of light always the same
« Reply #1 on: 10/05/2005 14:42:54 »

Take an experiment where a pulse of light travels from A to B. There are two events here: the light leaves A, and the light arrives at B. To find the speed of the light you divide the distance from A to B by the time difference between the light leaving and arriving.

If someone else who is moving in the same direction as the light observes the experiment they will disagree about how far the light has traveled (because they are moving relative to A & B, so they see A & B moving relative to them, so in the time between the events B will have moved towards where A was when the light departed).

Different observers moving at different speeds can still agree about the result of the experiment (the speed of light) even though they disagree about the distance the light has traveled. This is because they also disagree about the time it took. Our friend moving in the direction of the light will have experienced less time pass during the experiment.

This isn't much of an explanation and even so i have fudged some details, but it should give you an idea of the shift in priorities. In the Newtonian view space (distance) and time are agreed on by all observers while all speeds are relative, but in relativity the speed of light is agreed on by all, while space and time become relative to the observer to fit this.

I will try to explain some of the evidence for this if i get time later, unless someone would like to beat me to it.
« Last Edit: 10/05/2005 14:46:56 by moth »

#### qazibasit

• Sr. Member
• Posts: 344
##### Re: Speed of light always the same
« Reply #2 on: 30/05/2005 17:23:32 »
well Einstein is fake speed of light is not constant nothing which has particle nature can travel with a constant speed in this universe in the presence of gravity its just the lake of observation due to its very high speed

#### gsmollin

• Hero Member
• Posts: 749
##### Re: Speed of light always the same
« Reply #3 on: 30/05/2005 18:08:05 »
Sorry Q, its been measured many times in a gravitational field, and there is a red shift of wavelength, but fixed speed.

• First timers
• Posts: 4
##### Re: Speed of light always the same
« Reply #4 on: 20/06/2005 21:35:14 »
What in the known universe is not moving?  From only that point could there be a constant speed of light whereby all other light would base it's speed from.  In my opinion, to consider the speed of light from all emitting light bodies in motion as a constant, is equivilant to saying to earth is flat.  Consider our milkyway one of a hundred billion galaxies in the universe.  The light emitted from our gallaxy travels to the next neighboring galaxy , say Andromida, at 186,282mps.  If that galaxy is approching us at a rate of 360,000mph (hour), then the light would be recieved by (them) at a doppler shifted 6,000mpm (minute) or 100mps (second).

Lets consider a black hole.  We all understand that light emitted from the black hole can not escape the gravitational forces of the massive star.  Like a baseball tossed in the air, the light arcs and returns to the star.  On the flip side, external light that is captured by the black hole would accelerate as it approched the black hole.   If we believed it were a constant, then we'd have to believe that light can be affected by gravity to slow down but external light is unaffected by gravity and continues toward the black hole at it's "speed limit" 186,282mps.  To me, that's like saying the earth is round, but you'll fall of the edge if you go to far.

Lastly, I would like to argue the concept of speed.  Distance per unit of time.  Time is a man made concept.  The universe only knows motion.

A hundred years ago, a vast majority of the worlds population road horses.  In recent history, we've graduated from thinking the earth to be flat.  We've gradutated from the idea that the sun rotated around the earth.  When will we come to understand that the universe does not adjust it's "speed limit" to our medium sized galaxy, the milkyway.

« Last Edit: 22/06/2005 18:31:27 by Satalink »

#### realmswalker

• Sr. Member
• Posts: 205
##### Re: Speed of light always the same
« Reply #5 on: 20/06/2005 23:58:20 »
the universe adjusts its speed limit to light...

#### DoctorBeaver

• Naked Science Forum GOD!
• Posts: 12656
• Thanked: 3 times
• A stitch in time would have confused Einstein.
##### Re: Speed of light always the same
« Reply #6 on: 21/06/2005 08:32:56 »
Universal speed cameras?

#### qpan

• Sr. Member
• Posts: 260
##### Re: Speed of light always the same
« Reply #7 on: 28/06/2005 16:26:17 »
I don't understand what satalink means...
Light doesn't get pulled in by the black hole's gravity as photons have no mass - light follows the path of space and it is the space which is getting warped and distorted by the black hole's gravity leading to the light falling into the black hole... Therefore there's no need for it to accelerate in the first place, meaning that the speed of light is constant?

"I have great faith in fools; self-confidence my friends call it."
-Edgar Allan Poe

#### ukmicky

• Moderator
• Neilep Level Member
• Posts: 3011
##### Re: Speed of light always the same
« Reply #8 on: 04/07/2005 02:20:09 »
qpan
Thats how i understood it to be.
Because there is no gravitational force acting directly on the photon, the force of gravity is instead acting on the space or path the photon has no choice but to follow.
There has got to be a difference between the two.

And also i thought as far as the photon is concerned it is still travelling in a perfectly straight line and so in the photons frame of reference it should be totally unaffected.
so in my mind the photon is unaffected by gravity its the space that the photons are moving through that is affected

can anybody clear this up
« Last Edit: 05/07/2005 01:10:01 by ukmicky »

#### gsmollin

• Hero Member
• Posts: 749
##### Re: Speed of light always the same
« Reply #9 on: 05/07/2005 14:19:18 »
I think you've got it clearly already. The photon is freely falling, so it feels no gravitational force. The gravitational field acts on the space to curve it. The photon follows the spacial curvature, and moves in a geodesic.

• First timers
• Posts: 4
##### Re: Speed of light always the same
« Reply #10 on: 06/07/2005 20:40:48 »
Everything is fiction in regards to this topic...

Sept = 7;
Oct = 8;
Nov = 9;
Dec = 10;

#### Pablo

• Jr. Member
• Posts: 33
##### Re: Speed of light always the same
« Reply #11 on: 07/07/2005 04:26:39 »
the speed of light is a constant, this is a postulate of relativity and it doesn't require proof.

• First timers
• Posts: 4
##### Re: Speed of light always the same
« Reply #12 on: 09/07/2005 23:27:44 »
Last I checked, the "Theory of Relativity" was still a "Theory".

Sept = 7;
Oct = 8;
Nov = 9;
Dec = 10;

#### ukmicky

• Moderator
• Neilep Level Member
• Posts: 3011
##### Re: Speed of light always the same
« Reply #13 on: 10/07/2005 03:46:51 »
ive got a theory and my theory is that sooner or later
i will see your name in a reply to a future post
lets see if my theory is proved right

you always get one.

ps. you could always prove me wrong if you like
« Last Edit: 10/07/2005 03:54:47 by ukmicky »

#### stuffpuppet

• First timers
• Posts: 3
##### Re: Speed of light always the same
« Reply #14 on: 21/07/2005 17:37:11 »
quote:
Originally posted by qazibasit

well Einstein is fake speed of light is not constant nothing which has particle nature can travel with a constant speed in this universe in the presence of gravity its just the lake of observation due to its very high speed

#### stuffpuppet

• First timers
• Posts: 3
##### Re: Speed of light always the same
« Reply #15 on: 21/07/2005 17:43:27 »
Let us keep in mind that we have yet to discover the nature of all exhisting mass in the known universe.We are the fleas,trying to size up the dog,not to mention the elephant////I would guess that an anti-matter object would be subject to anti-mass environment to an equal degree...

#### darksat

• First timers
• Posts: 1
##### Re: Speed of light always the same
« Reply #16 on: 24/07/2005 21:50:26 »
E=MC times pie or pie inverted
Just a thought.

• First timers
• Posts: 4
##### Re: Speed of light always the same
« Reply #17 on: 26/07/2005 15:42:00 »
I see where you're going with that.  I've always had a problem with E=MC(squared) in that it does not account for area volume.  Light is indeed emitted in 3D.  So I would agree more with an equation that looked something like E=MC(Pie.R squared).   Exception being that I don't think that the speed of light is a constant.  So the C fails for me.

I've also toyed with the inversed equation (Big Bang?).  M = sq.rt(E/C)

Sept = 7;
Oct = 8;
Nov = 9;
Dec = 10;

#### Pablo

• Jr. Member
• Posts: 33
##### Re: Speed of light always the same
« Reply #18 on: 27/07/2005 22:30:17 »
The inverse of E= mc^2 is M= E/c^2, and this is the form that Einstein wrote it in his 1905 paper. (except that he used L for energy).

Pablo Gonzalez

#### simeonie

• Sr. Member
• Posts: 351
##### Re: Speed of light always the same
« Reply #19 on: 28/07/2005 11:58:52 »
cool! What exactly does E=MC^2 mean? I know it is like Mass times the speed of light squared makes mass. but how does this work?

----------------------
-__- my website!!!!
http://www.simeonie.co.uk
has forums too!

#### David Sparkman

• Sr. Member
• Posts: 234
##### Re: Speed of light always the same
« Reply #20 on: 28/07/2005 18:01:59 »
Energy = Mass * Velocity Squared is a newtonian concept. Einstein extrapolated that to Energy = Mass * the speed of light squared to say that 1) the speed of light was the maximum velocity, and that at that point the mass would turn into pure energy. It is an interesting thought, that he then poured a lot of thought into. It seems to work better than Newtonian physics so we use it for now. But do not dispare, there is always room for improvement.

And no, the speed of light is not constant. The speed of light appears to be constant in a vacuum (which is also mostly present in the low gravity form of space). Does gravity bend light as seen in the Einsteinium effect of distant stars? And why does light travel slower in air, water or oil? what is interacting with the photon to slow it down? Is it really the same photon that emerges or a photon that is regenerated from elastic reactions. But if so, why is the scattering angle so low. You know, there is a lot that we just don't know.

David

#### Pablo

• Jr. Member
• Posts: 33
##### Re: Speed of light always the same
« Reply #21 on: 28/07/2005 18:38:30 »

Pablo Gonzalez

#### vanvinhhoang

• Jr. Member
• Posts: 10
##### Re: Speed of light always the same
« Reply #22 on: 11/10/2005 11:25:11 »
Hey Simeonie, if u want to know how this formula perform, u could find in some nucleusphysical book. But i mean it is so hard to reach an exact explanation for it. the reason maybe our energy at maximum level < 100Tev ( as i know)

• Jr. Member
• Posts: 10
##### Re: Speed of light always the same
« Reply #23 on: 11/10/2005 15:45:33 »
1) Now, I'm not sure, if I'm correct or totaly crazy, David, but I got that idea, that actually, when light passes somethink, other than vacuum, it is absorbed, and almost at the same time, it is emmited, sometimes with different wavelength, sometimes with the same. But between those delays, the light would have the same speed. I'm not sure, if what I mean is clear.

2) I simply cannot agree with explanation of moth because, diegostation asked about when the source of the light is moving, and not when observer is moving next to the light.

3)"Lastly, I would like to argue the concept of speed. Distance per unit of time. Time is a man made concept. The universe only knows motion..
Time is not man made. It was here before we came. All that men did, was to start measuring the time and give certain period of time a name.
But if you say, that time is man made, it is the same, as saying, that  all the three dimensions are man made, because we gave them a name (length, width, and depth), and we also found some way to measure it. But we certainly didnt make them, that would probably mean, that men did the "Big Beng", or however the universe started.

#### syhprum

• Neilep Level Member
• Posts: 3770
• Thanked: 16 times
##### Re: Speed of light always the same
« Reply #24 on: 31/08/2006 19:31:31 »
David sparkman ask "why does light travel more slowly in a dielectric medium", the answer is that it does not!
What happens is that the photons are absorbed and then re emitted by the atoms of the intervening medium each time this happens there is a small delay but between atoms the photons travel at their normal speed

syhprum

#### The Naked Scientists Forum

##### Re: Speed of light always the same
« Reply #24 on: 31/08/2006 19:31:31 »