Is the speed of light constant or fixed

siarad · Nov 25, 2004

Says it all but to explain, light seems to be assumed fixed when measuring distances but is said to be constant. These seem at odds as we can't ever catch up light or run away from it.

Maddad · Nov 25, 2004

From any one point of view, refererenc, the speed of light is both constant and fixed.

siarad · Nov 26, 2004

Ay, there's the rub. William Shakespeare: Hamlet Act 3 scene 1 Makes the measurement of distance & M & M experiment nonsensical.

siarad · Dec 3, 2004

That's not what I mean. However we measure C we are always in a 'proper' position giving the same number. This means I can never measure its fixed speed which astronomy says is the same as the constant one used to measure distance. As I can't think of a way to measure its fixed speed I find it hard to believe in light years as distance. How can I jump outside of a 'proper' relativistic position to measure fixed C. C was measured a few centuries ago by occulting in a proper position. It was calculated, by Maxwell, which seems to be the closest approach to a non relativistic position M&M measured it in a proper position to find it constant. Michelson to his dying breath didn't believe in the result insisting it was a matter of accuracy. Einstein, reputedly not knowing of M&M, calculated it as constant. No-one seems to have measured its fixed speed so why do we rely on maths. If there's a way to measure fixed C please what is it?

siarad · Dec 4, 2004

I thought I did with the light year being related to distance. Isn't this outside of a proper frame of reference. If I travel to-wards a distant star my measurement of C is always the same despite running into light which makes it a constant but someone left on Earth would not see this. It's said time slows & distance contracts to account for this but we seem to have only mathematics, well differential equations, to prove this. I'm trying to find a way to measure C outside a proper frame. I'm trying to work out what Relativity actually means, well a bit more but I need this. OK I know only a handful of people understand relativity so I stand no chance.

Saiph · Dec 5, 2004

in any given reference frame, using "light-time" for distance (light years, light minutes etc) gives accurate distances. But you're right, different frames will not agree on a determined distance. Earth will think Alpha Centauri is ~4 ly away. A spacecraft heading there at .8c (relative to earth) will measure that distance as ~2 ly (IIRC). Then again, they both view the time it takes to make the trip differently as well. Its merely a matter of length contraction and time dilation. <div class="Discussion_UserSignature"> --------------------SaiphMOD@gmail.com -------------------"This is my Timey Wimey Detector. Goes "bing" when there's stuff. It also fries eggs at 30 paces, wether you want it to or not actually. I've learned to stay away from hens: It's not pretty when they blow" -- The Tenth Doctor, "Blink" </div>

alokmohan · Dec 6, 2004

Everything depends on frame of reference.But possibly speed of light is same in akll frameworks.Am I correct?

siarad · Dec 6, 2004

<blockquote>In reply to:<hr />Its merely a matter of length contraction and time dilation. <hr /></blockquote> Yes but why & what does this? What I'm trying to do is get outside of a proper relativistic time frame. Seems impossible but if I could maybe I'd understand relativity. It may be impossible 'cos we may need an extra dimension not available to us in order to do this. Take this triangle: Two objects far apart form each with a dichoic mirror Me at the apex of the triangle An object flashes a light to the other, some of which I see so can time the transit. Now I'm not in a proper frame with the transit between the two or am I? If I now travel to-wards the objects my frame changes but not the objects. So do I now see a different transit time or distance between the two objects? Be interesting, in the light of the weird two slit experiment, whether a single photon used as transit would travel both to me & the two objects.

igorsboss · Dec 6, 2004

Special relativity is based on two posutlates: 1) The physical laws are the same everywhere and everywhen. 2) The speed of light (in a vaccuum) is the same for each observer. Please note that #2 above is not a FACT, but a POSTULATE. It is merely assumed to be true! Einstien proved that these postulates imply special relativity. Since experimentalists have never contradicted special relativity, it remains the accepted theory. We use it merely because it is useful. However, nobody (to my knowledge) has ever proven that special relativity implies either of the postulates! The postulates might be incorrect! There might be a place or time where the physical laws break down. There might be an observer who observes a different speed of light in a vaccuum. We can never conduct enough experiments to absolutely verify these postulates. This is the first lesson in special relativity 101.

igorsboss · Dec 6, 2004

So do I now see a different transit time or distance between the two objects? YES! All observers who move relative to each other see the entire universe differently from each other. Time and/or distance are altered in such a way as to preserve the postulates. Therefore: There is no absolute space or absolute time. There is no center of the universe to which all observers would agree. There is no zero point of time to which all observers would agree. Contemplate this: The center of the universe is the bridge of my nose. This is the second lesson in special relativity 101.

siarad · Dec 6, 2004

Yes I've read about those experiments where high speed particles created by earths atmosphere can live 20 times longer than standstill laboratory ones. This is getting off topic but it is mine. Relativity certainly describes reality & I've used it for decades in my design work but now I'm retired I'm trying to understand it. What you've just said relies on time dilation but other similar things rely on mass increase. So there's a problem or just a different view. Take my favourite high speed electrons zooming down a CRT. These have to be corrected for mass increase to obtain the required deflection but could it also be a reduction in time for the electron thinking its spent less time being deflected. Well e/m = C^2 hasn't any time but surely it does as C, oddly for a constant, has dimensions & isn't just a number or am I wrong? Conversely could those particles of which you speak not see a time dilation but being more massive take longer to lose that energy. Incidentally I always see e/m = c^2 when constants should be capital letters, is there any significance in that. My above thought experiment was trying to use time from a different frame to open up relativity where we're normally locked into one frame. I've also on other topics asked if experiments have ever been carried out using an external time such as a pulsar to break out of relativity into reality but haven't had any replies.

wisefool · Dec 6, 2004

In a vacuum the speed of light is "c." However, under highly specific laboratory conditions light can be brought to a halt and stored, then liberated on command! See this web site for details: http://hackensackhigh.org/light.html

Saiph · Dec 6, 2004

the electrons don't see themselves as more massive. Instead they dont' think they got deflected as much, for 2 reasons: 1) They disagree with how long they were in the field (the big one) 2) They see a different field. Some of the E-field and some of the B-field are swapped (E becomes B when moving for example). <div class="Discussion_UserSignature"> --------------------SaiphMOD@gmail.com -------------------"This is my Timey Wimey Detector. Goes "bing" when there's stuff. It also fries eggs at 30 paces, wether you want it to or not actually. I've learned to stay away from hens: It's not pretty when they blow" -- The Tenth Doctor, "Blink" </div>

siarad · Dec 7, 2004

<blockquote>In reply to:<hr />1) They disagree with how long they were in the field (the big one)<hr /></blockquote> But we see it as increased mass, the formula used is m =e/c^2 where's the time & have no way of knowing how the electron sees it as we're trapped by Relativity. I'm trying to break free of it's shackles, the reason I asked about using an external time clock. Getting back to my thought experiment it seems the two remote objects are moved closer so maybe we don't need to travel space but bring it to us. Now would gravity be so great we couldn't step from Earth to a star? The other point I made was we don't know any distances in space merely the 'time of travel' unless C is fixed, something we can't measure being shackled by Relativity.

siarad · Dec 7, 2004

<blockquote>In reply to:<hr />2) They see a different field. Some of the E-field and some of the B-field are swapped (E becomes B when moving for example). <hr /></blockquote> Well I was thinking of magnetic deflection. A slow electron would corkscrew a whole circle & hit the top LH corner say. A faster electron would only go half a circle & hit the bottom RH corner. This is based upon mass & I don't know how to do it with time not being a scientist. I just wondered if mass & time are interchangeable as we don't seem to know what either are.

Saiph · Dec 7, 2004

Actually, the equation being used isn't e=mc^2. That equation actually tells you about converting energy to mass and vice versa. The "m" in this equation isn't the relativistic mass at all, but rather the rest mass, or Mo (subscript on that "o"). The energy describing a mass increase due to velocity (notice that isn't in that equation) is the relativistic kinetic energy. Its KE= 1/(sqrt(1-V^2/C^2) * mv^2 The 1/(sqrt....) is the symbol "gamma" and is the standard relativistic correction factor. This, when lumped in with the M (i.e. "gamma" * M) tells you the relativistic mass (or increased resistance to acceleration, since the actuall mass, used in e=mc^2, doesn't really increase). The time factor (and the distance traveled factor) is hidden in the velocity, since V=D/T. As for magnetic deflection, the reason the particle sees E as B, and vice versa, is because of their causes. A moving electric charge creates a magnetic field. If we create an electric field in our frame, we use a lot of stationary charges. However, someone moving relative to our frame, will see those "stationary" charges moving w/ respect to them. And thus they measure a magnetic field comming from them as well (with a decrease in electric field). If we create a magnetic field, we do it by using moving charges. Someone moving relative to us will see them moving too, but at a different rate, and thus at a different strength. And as some charges become more stationary, the electric field increases as well. <div class="Discussion_UserSignature"> --------------------SaiphMOD@gmail.com -------------------"This is my Timey Wimey Detector. Goes "bing" when there's stuff. It also fries eggs at 30 paces, wether you want it to or not actually. I've learned to stay away from hens: It's not pretty when they blow" -- The Tenth Doctor, "Blink" </div>

Saiph · Dec 7, 2004

Anyway, we see the electron hit a spot on the screen. The electron see's itself hitting the same spot on the screen. On that, we agree (we have to, otherwise we see two irreconcilable consequences of it's actioins). However, why the electron got there, is where the disagreement arises. We see it travel for a while in a weak field. It sees itself travel a shorter time, a shorter distance, through a stronger field. The end result: It hits the same spot in both fields of reference. <div class="Discussion_UserSignature"> --------------------SaiphMOD@gmail.com -------------------"This is my Timey Wimey Detector. Goes "bing" when there's stuff. It also fries eggs at 30 paces, wether you want it to or not actually. I've learned to stay away from hens: It's not pretty when they blow" -- The Tenth Doctor, "Blink" </div>

siarad · Dec 9, 2004

So time & mass aren't different views of the same actions. Does this mean that accelerating, which becomes increasingly difficult, is due to mass increase & not due to the shorter time available to apply the energy.

Saiph · Dec 9, 2004

it is due to an inertia increase, yes. Note: I said inertia as opposed to mass, since at relativistic speeds those two things are not the same. Mass refers to the amount of matter in an object, or the rest mass. Inertia is the resistance to acceleration. Combining the two and you get the poorly named "relativistic mass". <div class="Discussion_UserSignature"> --------------------SaiphMOD@gmail.com -------------------"This is my Timey Wimey Detector. Goes "bing" when there's stuff. It also fries eggs at 30 paces, wether you want it to or not actually. I've learned to stay away from hens: It's not pretty when they blow" -- The Tenth Doctor, "Blink" </div>

alokmohan · Dec 10, 2004

Can I say if a thing travels with speed of light its relativistic mass is infinite?

Saiph · Dec 10, 2004

sure, except you can't get there (requires to much energy to shift an near infinite inertial mass). And so the only way to get there is to have no rest mass (i.e. the increased inertia factor is multiplied by zero, so it doesn't matter). And that means you're a photon, and thus massless. <div class="Discussion_UserSignature"> --------------------SaiphMOD@gmail.com -------------------"This is my Timey Wimey Detector. Goes "bing" when there's stuff. It also fries eggs at 30 paces, wether you want it to or not actually. I've learned to stay away from hens: It's not pretty when they blow" -- The Tenth Doctor, "Blink" </div>

siarad · Dec 10, 2004

Saiph Yes I do appreciate the difference over mass but it's what gets used. In my 'scope above it works perfectly by calculating the increased mass from e/m = C^2. Your more expansive formula isn't necessary as rest e/m is known courtesy of scientists so we designers do it the easy way. I did put a topic about the way words are used in possibly 3 different ways giving much confusion to unscientific people like me trying to tie subjects together. Getting back to my topic, I'm not sure whether I'm any wiser so: 1 c is fixed but not measurable 2 measuring c always gives the same answer 3 c is assumed to be the constant value found in 2 Therefore we can run into or away from light just as sound but can't measure the speed differential.

siarad · Dec 11, 2004

<blockquote>In reply to:<hr />Wrong. Light will always run away from us and will always reach us. We cannot reach or exceed light speed. That is an experimental fact. No matter how fast or slow we travel, relative to some reference frame, light will always travel at light speed. <hr /></blockquote> Yes but at which speed the 'fixed' or the measurable 'constant' is all I'm asking. <blockquote>In reply to:<hr />relative to some reference frame<hr /></blockquote> No relative to our reference frame 'cos we can't be anywhere else. I'm not using logic but explanations from previous topics which don't make sense unless you're wrong. That doesn't make me right as there could be alternatives.

siarad · Dec 11, 2004

Thanks for the interesting links but that's not my topic problem. Irrespective of the actual value of C the fixed value used for distance measurement is taken as the measured value which is constant, a value which I previously posted has been calculated too. I have a problem with these two being the same, unless they are different although numerically equal I can't understand another topic.

siarad · Dec 11, 2004

No that's the constant speed, the only one we can measure.

Is the speed of light constant or fixed

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