The speed of light; another perspective.

[swainy]

Next thing you will be saying is, Is the speed of light slowing down. Oops That's another thread sorry.

http://www.opfocus.org/index.php?topic=story&v=8&s=4

tc

[Henning Makholm]

Next thing you will be saying is, Is the speed of light slowing down. Oops That's another thread sorry.
http://www.opfocus.org/index.php?topic=story&v=8&s=4

Among the conceivable "small" modifications of the current king-of-the-hill theories (GR & standard model), the following classes:

1. Theories where the speed of light in vacuum varies from place to place and/or from time to time.
2. Theories where Planck's constant varies from place to place and/or from time to time.
3. Theories where the gravitational constant varies from place to place and/or from time to time.
4. Theories where the rest masses of all elemental particles as well as various coupling constants vary in unison from place to place and/or from time to time.

are all mathematically equivalent in the sense that any theory from one of these classes is trivial to reformulate as one from any of the other classes such that the reformulated theory makes exactly the same predictions. The only way of choosing between them is esthetics and computational convenience.

Of the four possibilities, c and h are currently understood as so fundamental to the structure of time and space that class (1) and (2) are extremely undesirable to physicists. Class (3) is only a little better. On the other hand, (4) would probably be much more palatable, not less because all of the quantities it asserts to vary are ones that the current theories neither manage to explain[*] nor depend on on any really deep level. Furthermore, class (4) allows for further tinkering in which all rest masses to not change completely uniformly, which is a benefit compared to not even being able to express that possibility.

Therefore, if Sanejouand's theory has merit (on which I express no opinion), I would expect the vast majority of physicists to favor its class (4) formulation, unless there are strong internal reasons in the theory that favor one of the others. But that doesn't sound nearly as wondrous in a popular piece such as the linked one.

[*] Various GUT candidates appear to promise to improve on this, but have as far as I'm aware not quite delivered on that promise.

[wonderboy]

The speed of light is constant, I know this and I am not arguing otherwise. Whether it is inches, miles, metres or whatever aliens measure distance in, it will be the same speed.

What I'm saying is, that if me and some alien dude were sitting at the starting line of a race to a distant planet. I might say that the planet is "10 light years away" based on my assumption of what a year is, and the alien may say that the planet is "5 light years away" because his home planet takes longer to orbit its parent star meaning his ideas of how long light takes to travel a year is different.

I'm not arguing over the speed of light, merely its understanding to someone with different understandings of distance and yearly orbits on a different planet.


Paul.

[Henning Makholm]

What I'm saying is, that if me and some alien dude were sitting at the starting line of a race to a distant planet. I might say that the planet is "10 light years away" based on my assumption of what a year is, and the alien may say that the planet is "5 light years away"

Yes, but so what? Why is the alien even speaking English? If he learned English in order to speak to you, he should use the word "year" to mean your year; everything else just creates confusion. If he's not speaking English, then how do you find it even remotely interesting that your "lightyear" is a different unit from his "w1qasrek!sl"? And if he's speaking English because the very same language just happened to evolve on his planet, then you're clearly in a bad science fiction movie and you can expect nothing to make sense at all.

[Chris Peterson]

I'm not arguing over the speed of light, merely its understanding to someone with different understandings of distance and yearly orbits on a different planet.

I'm afraid I don't see how the use of different units produces a different understanding. If I go into the store and buy a quarter pound of cheese, and somebody in Europe goes into the store and buys 100g of cheese, I expect each of us has exactly the same sense of how much we are getting. If I use their units, or they use mine, we both might "know" how much we're getting but have a different sense- that's just unfamiliarity with the units. But that doesn't apply to us and aliens, each using our comfortable units of stellar distance.

[swainy]

I'm not arguing over the speed of light, merely its understanding to someone with different understandings of distance and yearly orbits on a different planet.

I'm afraid I don't see how the use of different units produces a different understanding. If I go into the store and buy a quarter pound of cheese, and somebody in Europe goes into the store and buys 100g of cheese, I expect each of us has exactly the same sense of how much we are getting. If I use their units, or they use mine, we both might "know" how much we're getting but have a different sense- that's just unfamiliarity with the units. But that doesn't apply to us and aliens, each using our comfortable units of stellar distance.

Every language can be translated, To English. As Chris said, Physics is much the same. The numbers may appear different but they are not. Just a different language.

tc

[makc]

...somebody in Europe goes into the store and buys 100g of cheese...

Europe?

[swainy]

Check out the Grey patches. You trying to tell us something?

tc

[Chris Peterson]

Europe?

Just an example <g>.

[swainy]

Next thing you will be saying is, Is the speed of light slowing down. Oops That's another thread sorry.

http://www.opfocus.org/index.php?topic=story&v=8&s=4

tc

No bite yet then? What does the link, change in the universal constant?

I have been looking into this. I have read some very interesting things on this. Post pending tray?

tc

[Chris Peterson]

No bite yet then?

Perhaps because there's really no story. There have been occasional suggestions over the years that various physical constants are not actually constant. This is another such claim. It is highly speculative and poorly tested. At the moment, there is a vast amount of evidence that suggests c actually is a constant, and hasn't changed since the current physical laws crystallized out of the Big Bang. The possibility remains interesting, but there's really nothing at this point to discuss.

[The Code]

No bite yet then?

Perhaps because there's really no story. There have been occasional suggestions over the years that various physical constants are not actually constant. This is another such claim. It is highly speculative and poorly tested. At the moment, there is a vast amount of evidence that suggests c actually is a constant, and hasn't changed since the current physical laws crystallized out of the Big Bang. The possibility remains interesting, but there's really nothing at this point to discuss.

So reports say light could be slowing down, over billions of years. And scientist can actually stop light by Freezing it through Very cold gas. :

http://www.sciencentral.com/articles/vi ... =218392702
http://physicsworld.com/cws/article/news/3013

So, I here space is very cold, And Full of Gasses. Can you actually tell, from looking at any part of the CMB the speed at which you are seeing those photons traveling at?

tc

[Chris Peterson]

So reports say light could be slowing down, over billions of years.

That's not what is being suggested. The article refers to the (slim) possibility that c has changed over time. This has nothing to do with the speed of light, other than the fact that the fastest light can travel is c. There is no lower limit on the speed of light.

And scientist can actually stop light by Freezing it through Very cold gas... So, I here space is very cold, And Full of Gasses. Can you actually tell, from looking at any part of the CMB the speed at which you are seeing those photons traveling at?

Space is neither cold, nor full of gas. When you play around with the velocity (or phase velocity) of light in a Bose-Einstein condensate, you are working at a temperature of microkelvins. The Universe is bathed with radiation that is 2.7 K - millions of times hotter than you need for these effects. In addition, most of the Universe is nearly empty of gas. The refractive index of any region of the Universe is so close to 1 that we can safely say that every photon we record from the CMB is traveling at c.

[swainy]

Space is neither cold, nor full of gas. When you play around with the velocity (or phase velocity) of light in a Bose-Einstein condensate, you are working at a temperature of microkelvins. The Universe is bathed with radiation that is 2.7 K - millions of times hotter than you need for these effects. In addition, most of the Universe is nearly empty of gas. The refractive index of any region of the Universe is so close to 1 that we can safely say that every photon we record from the CMB is traveling at c.

Just for the interest, and the reading only.
I don,t no how you can say that with any form of certainty. Check out the Apod pillars of creation. http://antwrp.gsfc.nasa.gov/apod/ap100328.html Then tell me our universe has not changed in transparency in 6 billion years. Bering in mind, Class 1,? and 2 generation stars. http://www.universetoday.com/2010/03/03 ... milky-way/ Creating more pillars of creation more nebula gas dust etc etc. And then times this by billions into a smaller 8 billion year old universe. somebody once told me. There are more stars in the universe than grains of sand on every beach. That,s just stars, now add all 8 planets for every star, and billions on tons of other size rocks etc etc. But I don,t need all the grains on every beach, I just need a hand full. Because with just a hand full I can,t see the skin of my palm. So how can a little photon, travel 14 billion light years x 6 trillion miles of gas, dust and all other stuff we have no knowledge of? There may be no gas and dust there now. But five billion years ago?

But any hows, how can light be a constant if it can be slowed down? Does this mean something can slow gravity down? and as gravity may control time, does that mean we can physically manipulate almost anything?

tc

[Chris Peterson]

I don,t no how you can say that with any form of certainty. Check out the Apod pillars of creation. http://antwrp.gsfc.nasa.gov/apod/ap100328.html Then tell me our universe has not changed in transparency in 6 billion years.

I didn't say that. What I said is that most of the Universe is largely empty space, and theory tells us that has been the case since very shortly after the BB. Even in regions like the Pillars of Creation, what you see would be considered a hard vacuum in any laboratory. It isn't a medium with a refractive index different than one, which means the speed of light is not affected by it.

But any hows, how can light be a constant if it can be slowed down?

As previously noted, the speed of light is not a constant. That belief is a common misconception. There is a universal constant called c, which shows up in many physical theories. The velocity of light in a vacuum happens to be equal to c. That does not mean that c is the speed of light, and it does not mean that the speed of light is a constant. The index of refraction of a medium defines the amount by which light travels slower than c.

Does this mean something can slow gravity down? and as gravity may control time, does that mean we can physically manipulate almost anything?

Gravity certainly does not "control time". Whether the speed of gravity can be something other than c is an interesting question- essentially, it is asking if there is something like an index of refraction for gravity. I don't know that anybody can answer that beyond speculation. I very much doubt that anything modifies the propagation speed of gravity enough to produce anything but very subtle observational effects, however.

[swainy]

Gravity certainly does not "control time". Whether the speed of gravity can be something other than c is an interesting question- essentially, it is asking if there is something like an index of refraction for gravity. I don't know that anybody can answer that beyond speculation. I very much doubt that anything modifies the propagation speed of gravity enough to produce anything but very subtle observational effects, however.

I,m sorry to say, that I have a strong belief that Gravity is connected to Time. But not in this thread.

But, I would like to say, you have made my day, by posting the above Thanks Chris.

tc

[StarstruckKid]

I think what wonderboy was getting at was the difficulty of communicating with the inhabitants of another world how each side measures fundamental quantities like the speed of light (c). Not only are inertial frames of reference all local, so are systems of measurement.

Suppose we managed to establish radio contact with the inhabitants of Bftsplk and we want to talk about the speed of light. Here on Earth we measure it in distances based on things like the diameter of the planet (the meter) or the length of the King's royal pedal extremities (the foot) extended to how many times the King can put one foot in front of the other before he gets tired (5280, a mile). Our time measurements are based on the rotational speed of the Earth and the apparent size of the Sun (and Moon). Since the angular size of the Sun is about 1/2 degree, it takes almost exactly 2 minutes to pass a given fixed reference point.

But on Bftsplk, the unit of length is based on the size of the average Bftsplkian's facial tentacle (very democratic beings, those Bftsplkians) or a frbzzle, and their unit of time is based on how long it takes the average Bftsplkian to fall a distance of 1717 (did I mention they have 17 tentacles?) frbzzles, or a hhrrrrckkk. Also did I mention they are about the size of a terrestrial palmetto bug? They have determined that the speed of light is 98-13/17 vrsook (I won't attempt to explain their numeric system) frbzzles per hhrrrrckkk.

To make matters worse, our planets have a large differential velocity, so the Doppler effect prevents using the frequency of the radio wave as a reference.

BUT, we can get away from local units of measure, and dispense with defining c in those terms by turning the problem upside down. Start with the fundamental constant, c, and work backwards. Much as we dispensed with the old cycles per second yardstick with frequency and now call one cycle per second a Hertz (not a fundamental quantity, however, it's still based on the second).

So then we measure how long it takes our radio signal to go to Bftsplk and back,(they'd have to have a repeater pointed back at us), we tell them it was x seconds, they tell us it was y hhrrrrckkks, and voila! we now know how many seconds per hhrrrrckkk.

Now we just need to rework our road signs. I will no longer be driving 60 miles per hour, it will be, oh, about 90 nano-c's, if I've figured right.

Michael

[Henning Makholm]

To make matters worse, our planets have a large differential velocity, so the Doppler effect prevents using the frequency of the radio wave as a reference.
....
So then we measure how long it takes our radio signal to go to Bftsplk and back,(they'd have to have a repeater pointed back at us), we tell them it was x seconds, they tell us it was y hhrrrrckkks, and voila! we now know how many seconds per hhrrrrckkk.

If we have a large differential velocity, there will be relativistic time dilation to take into consideration, so the two ends will not be measuring the same amount of time. (In fact, due to the mutual velocity, successive radio messages will not even have the same distance to travel).

Much better simply to send them the SI definitions of the second and meter, and have them build a cesium clock to get their own realization of the second. Or transact all our business in natural units.

[swainy (tc)]

Gravity certainly does not "control time".

Are you sure about that? So Why does a bigger Mass, Slow time down? To A point, Where T=0 ? What are the Connections that make this so? Why would there be, any connections?

tc

[Chris Peterson]

Gravity certainly does not "control time".

Are you sure about that?

Yes.

So Why does a bigger Mass, Slow time down?

It doesn't. You don't understand the most basic aspect of different reference frames. Time always flows the same. It only appears different from different frames.

[swainy]

So Why does a bigger Mass, Slow time down?


It doesn't. You don't understand the most basic aspect of different reference frames. Time always flows the same. It only appears different from different frames.

No, Not according to Hawking. Time travel is possible, Either way. (With the Tech). You don,t get out of it that easy. The Clocks are different, I saw them with my own eyes, Its been proven. So I will ask again. What is the connection, Between Time And Mass?

tc

[Chris Peterson]

No, Not according to Hawking. Time travel is possible, Either way. (With the Tech). You don,t get out of it that easy. The Clocks are different, I saw them with my own eyes, Its been proven. So I will ask again. What is the connection, Between Time And Mass?

You don't understand Hawking, either. Or what you get from him you get from some of his popular work, which is technically wrong.

Time is not affected by mass. Two different reference frames in different gravitational fields will each see time in the other moving at different rates. That's what we learn from relativity. It doesn't mean that time itself is affected. Comparing time between two non-inertial frames is non-trivial. But the important point is that it is a comparison. From within either frame, time flows exactly as always. There is no way to tell if your local time is somehow "fast" or "slow"; that doesn't even have any meaning.

[swainy]

There is no way to tell if your local time is somehow "fast" or "slow"; that doesn't even have any meaning.

We are getting somewhere,

I do understand Chris, I am just playing with it. 5 years orbiting our black hole, is ten years on Earth, Vice verse. Some what different with the speed of light. Its what the paradox is all about. But your not going to show me how, Time is not effected by Mass in any meaningful way ? Huh?

tc

[Chris Peterson]

I do understand Chris, I am just playing with it. 5 years orbiting our black hole, is ten years on Earth, Vice verse. Some what different with the speed of light. Its what the paradox is all about. But your not going to show me how, Time is not effected by Mass in any meaningful way ? Huh?

There is no paradox. Only something that seems contrary to our everyday experience.

[swainy]

I do understand Chris, I am just playing with it. 5 years orbiting our black hole, is ten years on Earth, Vice verse. Some what different with the speed of light. Its what the paradox is all about. But your not going to show me how, Time is not effected by Mass in any meaningful way ? Huh?

There is no paradox. Only something that seems contrary to our everyday experience.

Remember you heard it from me first.

tc