Naked Science Forum
General Science => General Science => Topic started by: Brian Starkey on 04/12/2009 12:30:03
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Brian Starkey asked the Naked Scientists:
Dear Chris,
Why is the speed of light the speed it is? What limits it to around 300,000kps. Why does it not go any faster, after all photons have no mass? For that matter why is it not slower? Is, as some claim, the speed of light in fact slowing down and was around four times its present speed at the beginning of the universe. If this is true what happens to the famous equation E=MC2 when the value of C is reducing?
Just reading this it would seem that there could be a whole programme needed to cover the subject properly. Anyway, I would be very interested to hear even a short version of why the speed of light is the speed it is.
Kind regards,
Brian Starkey
What do you think?
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This is a very good question. There are some very good reasons why it is a finite and invariant value, but not for it being the specific value that it is.
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There are at least 3 kinds of answers:
1. c = 299,792,458 m/s by definition.
2. Before we defined c as that number, light speed was that value also because of units: in miles/second is ~ 186,000, in parsec/year is ~ 0.3068, in other units it's another value. In some units it can be 1, or 2 or 1/1000 or any value you want.
3. Having fixed the units of space and time, light speed resulted to be that number because of the electromagnetic properties of the void (dielectric constant, for example).
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In some respects it can be thought of as part of this:
http://en.wikipedia.org/wiki/Anthropic_principle
"In physics and cosmology, the anthropic principle is the collective name for several ways of asserting that the observations of our physical universe must be compatible with the life observed in it. The principle was formulated as a response to a series of observations which seemed to show that the laws of nature and its physical constants were uncannily set in a way that allowed conditions for life. The anthropic principle states that this apparent coincidence is actually a necessity because we wouldn't be able to exist, and hence, observe the universe, were these laws and constants not set this way."
...bit of a cop out answer though, I know!
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Well we don't even know if light travel.
there are some ideas in which you neen both a transmitter and a receiver for any light to exist, sounds corny but it's true. And if so only the light you perceive should then be existent. Hmm, sounds self evident that one but it's not. what it stated is that its not enough with the transmitter (Sun).
Then you have 'sum over parts' where light can bee seen to take all possible ways in the same time, but with different probability. If that one would be true then one photon can be seen to fill up a considerable part of space. Perhaps all.
The only proof of photons are their impact. As far as I know you can't track them as they 'travel'.
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It's an interesting idea yor_on, but if the light is not actually traveling across the distance between the emitter and detector then what is it doing, or where has it gone during the period of time it takes between being emitted and being detected?
The idea of light not actually traveling between emitter and detector also seems to introduce some causality problems too. For example, let's say we set up a light emitter and detector system and set the emitter to send a flash of light towards the detector at a certain time. However, in the period of time between the light being emitted and then being detected, we quickly stick another detector in front of the original detector to intercept the light before it reaches the original detector. Now when the light was emitted, the second detector wasn't in the way, so it would expect to appear at the original detector, but when we put the second detector in place we detect the light there instead, so how does the light know, after it has been emitted, that it now needs to appear somewhere else?
If the emission and detection of the light is simultaneous, it gets around this problem, of course, but it then means that there must be some other timing mechanism in place to account for the apparent difference in time between emission and detection.
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It gets worse. A photon arrives in "no time al all" (relative to its own timeframe). If it covers distance in no time, its speed is infinite.
Of course, that is not true relative to our timeframe.
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It gets worse. A photon arrives in "no time al all" (relative to its own timeframe). If it covers distance in no time, its speed is infinite.
Of course, that is not true relative to our timeframe.
No its speed is not infinite. It doesn't even have a speed from its frame of reference.
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It gets worse. A photon arrives in "no time al all" (relative to its own timeframe). If it covers distance in no time, its speed is infinite.
Of course, that is not true relative to our timeframe.
No its speed is not infinite. It doesn't even have a speed from its frame of reference.
Did its position move? I think so.
Did it take any time to move? I think not.
It travelled distance in zero time.
Last time I checked, velocity was equal to distance divided by time. Why is the velocity not infinite?
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If a photon (from its frame or non-frame of reference) does not experience a passing of the time dimension, then invariantly it cannot move through space either from its perspective, making speed irrelevent.
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But you where certainly right when you said:
Of course, that is not true relative to our timeframe.
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If a photon (from its frame or non-frame of reference) does not experience a passing of the time dimension, then invariantly it cannot move through space either from its perspective, making speed irrelevent.
Apparently, the photon is unaware of that limitation, so it does it anyway. This may also help to explain why photons don't seem to "get tired", regardless of the distance they travel. They don't have time to get tired!
I prefer to think of photons as energy "quanta" propagating through Space by means not fully understood. They certainly are pretty amazing.
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It gets worse. A photon arrives in "no time al all" (relative to its own timeframe). If it covers distance in no time, its speed is infinite.
Of course, that is not true relative to our timeframe.
I don't think it's safe to assume that photons experience no time on the basis of relativistic time dilation. Relativistic time dilation relates to accelerating masses and light neither accelerates, nor has mass.
Also, dividing a number by zero and declaring the answer to be infinity is a mathematical trick but doesn't apply to the real world; if you divide one apple by zero, what are you left with? ...one apple.
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It gets worse. A photon arrives in "no time al all" (relative to its own timeframe). If it covers distance in no time, its speed is infinite.
1. A photon's frame of reference doesn't exist.
2. If you want to consider a massive object with speed very near to c, then it's true it goes in almost no (its) time where you want, but in its frame of reference the distance is almost zero as well (Lorentz contraction). Its speed is exactly the same from wherever frame you measure it.
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If a photon (from its frame or non-frame of reference) does not experience a passing of the time dimension, then invariantly it cannot move through space either from its perspective, making speed irrelevent.
Apparently, the photon is unaware of that limitation, so it does it anyway. This may also help to explain why photons don't seem to "get tired", regardless of the distance they travel. They don't have time to get tired!
I prefer to think of photons as energy "quanta" propagating through Space by means not fully understood. They certainly are pretty amazing.
Aware? A photon is not aware of anything. And even if it could be aware, its birth and death would be simultaneous ref: Fred Alan Wolf PhD ''Spiritual Universe''.
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its birth and death would be simultaneous ref: Fred Alan Wolf PhD ''Spiritual Universe''.
Thank you. This is tantamount to decaring that a photon's velocity is infinite.
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its birth and death would be simultaneous ref: Fred Alan Wolf PhD ''Spiritual Universe''.
Thank you. This is tantamount to decaring that a photon's velocity is infinite.
Nope. It's tantamount to say the effect is instantaneous, no speed required.
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If we want to increasingly split hairs, or even infinitives.
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Why split hairs...?
For something with an infinite speed it would actually oscillate throughout the time dimension. All indications of relativity point to a photons experience being not existent at all from it's ''frame of reference''. Only hypothetical tachyons experience such an oscillations.
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All indications of relativity point to there not being a frame of reference for a photon.
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Anyway,
when everyone has stopped worrying about a photon's point of view (and, obviously, you wouldn't want to hurt its feelings) the answer is that the speed of electromagnetic radiation falls out of Maxwell's equations.
It is dependent on the fundamental properties of a vacuum and the numerical value depends on what units you measure the permitivity and permeabillity of the vacuum in.
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Anyway,
when everyone has stopped worrying about a photon's point of view (and, obviously, you wouldn't want to hurt its feelings) the answer is that the speed of electromagnetic radiation falls out of Maxwell's equations.
It is dependent on the fundamental properties of a vacuum and the numerical value depends on what units you measure the permitivity and permeabillity of the vacuum in.
That's true. Photons can be very sensitive.
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All indications of relativity point to there not being a frame of reference for a photon.
That why i hyphenated it.
''frame of reference''
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Anyway,
when everyone has stopped worrying about a photon's point of view (and, obviously, you wouldn't want to hurt its feelings) the answer is that the speed of electromagnetic radiation falls out of Maxwell's equations.
It is dependent on the fundamental properties of a vacuum and the numerical value depends on what units you measure the permitivity and permeabillity of the vacuum in.
Yes
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That's true. Photons can be very sensitive.
[/quote]
LMAO..nice!
LMAO!, that made my night!Anyway,
when everyone has stopped worrying about a photon's point of view (and, obviously, you wouldn't want to hurt its feelings) the answer is that the speed of electromagnetic radiation falls out of Maxwell's equations.
It is dependent on the fundamental properties of a vacuum and the numerical value depends on what units you measure the permitivity and permeabillity of the vacuum in.
That's true. Photons can be very sensitive.
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All indications of relativity point to there not being a frame of reference for a photon.
That why i hyphenated it.
''frame of reference''
What hyphens?
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All indications of relativity point to there not being a frame of reference for a photon.
That why i hyphenated it.
''frame of reference''
What hyphens?
Link to this post 288399 - the previous page.
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All indications of relativity point to there not being a frame of reference for a photon.
That why i hyphenated it.
''frame of reference''
What hyphens?
Link to this post 288399 - the previous page.
OFGS - My fault.. not hyphenate. The last thing i want to do is confuse this thread anymore. Sorry.
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Thank you Sadarian.
I am glad that you are paying attention. The rest of these twits would not appreciate humour even if it was a kipper smacking them in the face.
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Thank you. This is tantamount to decaring that a photon's velocity is infinite.
Did you read my post (of the 05.12.2009)?
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Thank you. This is tantamount to decaring that a photon's velocity is infinite.
Did you read my post (of the 05.12.2009)?
Why didn't you just say "today"? Oh, maybe you mean May? I'm sure I did, and it probably points out that I don't know what I'm talking about, which may well be correct. [:D]
Nope, nothing relevant in May, so it must be the one in this thread that says photons have no frame of reference. I would not argue with that. I saw your post, but I was too busy jousting with Mr S to respond.
My comments about infinite speed should be taken with a large grain of salt. However, I do believe we still have a lot to learn about photons.
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Thank you Sadarian.
I am glad that you are paying attention. The rest of these twits would not appreciate humour even if it was a kipper smacking them in the face.
To be fair, nost people only apreciate that sort of humour when it's someone else's face getting smacked.
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Thank you Sadarian.
I am glad that you are paying attention. The rest of these twits would not appreciate humour even if it was a kipper smacking them in the face.
To be fair, nost people only apreciate that sort of humour when it's someone else's face getting smacked.
Ouch!! [B)]
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Geezer, take a look here.
http://www.physicsforums.com/archive/index.php/t-209191.html
But it's difficult discussing a 'time frame' when relativity flatly states that there are none, as seen from a photon. That's one of the reasons why I tend to look at them as not 'traveling' at all.
http://en.wikipedia.org/wiki/Virtual_particle#Virtual_particles_in_Feynman_diagrams
As for Wheeler–Feynman absorber theory
The Wheeler-Feynman model, called the "absorber theory of radiation," makes electromagnetism a two-way street as far as the time dimension is concerned. They based their time-symmetric theory on the assumption that every light wave emitted by an atom must be absorbed by another atom and that these two events, light emission plus light absorption, should be considered as a single inseparable process. In it they see ‘time’ as going backward from the sink (your eye), which is cases allowed by both Dirac's equation and Maxwell's wave equation for light, as well as it goes forward in time from the source (sun). As a result any light observed will need both factors to exist (Source and sink)
http://en.wikipedia.org/wiki/Wheeler%E2%80%93Feynman_absorber_theory
http://www.npl.washington.edu/npl/int_rep/dtime/node2.html
And some different interpretations of it.
http://arxiv.org/abs/physics/0104066 (Free)
http://www.iop.org/EJ/abstract/0305-4470/15/4/026
http://www.springerlink.com/content/g86km360t11971x3/