I'm somewhat confused.
The above would appear to be a statement of disagreement. Yet this
appears to be making my point.

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Science is like sex. Sometimes something useful comes out, but that is not the reason we are doing it.
-- Richard Feynman

This is one of those "I'm going to think about these things until my head explodes" kind of threads.

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I'm like one of those idiot savants...well, except for the savant part.
"In order to increase awareness of the homeless, security have been given binoculars."

Yeah I know that feeling. The only way to avoid is to stuburnly ignore modern theoretical physics and look into another direction if it shows up. I decided to do so after I passed my "Vordiplom" (an intermediate Examen after the 4th semester) and turned to applied and experimental physics.
Unfortunately from time to time it comes and takes a look at me and than I am ending up as you do. sigh!

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Andre

"They did not know it was impossible, so they did it!"
Mark Twain

Indeed. And I would tend to think that permittivity and permeability must really be just one physical thing-- their product. Their individual values should be 100% pure convention-- there cannot be two physical parameters there, only one. That's also what publius was saying.
Yes, the best approaches generally focus on dimensionless constants-- those are the only ones that are "real".

Yes, all this can get very confusing because it gets very deep and makes you have to think about things at the very architectural level. :-)

My point was the mu-epsilon form of Maxwell can lead one astray into the view that 'c' is merely an electromagnetic property that depends on pure EM properties. Namely, there are two independent degrees of freedom, the magnetic and the electric force constants that give us 'c'.

And that is not correct. For example, consider two charges held stationary by a spring, say. In the rest frame, there is a pure electric force being offset by the force of the spring. Now go to a moving frame. The electric force gets transformed into both electric and magnetic terms. The magnetic component is in the opposite direction of the electric force in that frame.

Well, equilibrium must be preserved, and you find the spring force must transform in the exact same way to preseve equilibrium (there might even be some cute way to pull out some magnetic looking analog there, but that usually isn't done as it probably isn't very useful). A spring has nothing to do with EM, yet 'c' governs that transform in the same way it governs the transform of E into B.

And go to gravity and General Relativity and you find a similiar (although much more complicated) gravitomagnetic component, governed by the same c.

This 'c' is much more fundamental. It is a property of the geometry of space-time itself. EM, gravity, and spring forces simply play out against the geometric background. It is really just an accident of history that we first stumbled onto 'c' via EM means.

There is only one degree of freedom with EM, and that's simply wrapped up in one force constant, which is determined by your chosen unit of charge.

My last statement was if we wished to give ourselves the illusion of two degrees of freedom in EM units, we have to take one away from our space and time freedom, which would then affect how gravity, springs, etc transform as well.

-Richard

But I did not say that c is purely an EM property, nor that there are two independent degrees of freedom for EM. I said that you can get the value of c by measuring other things, and offered mu and epsilon as an example.

By the number "free parameters" I, evidently clearly as mud, meant to refer to the number of independent physical constants. We have some chose exactly which constants we call use (trivial example: h or h-bar), but their number (and significance) is give by nature.

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Science is like sex. Sometimes something useful comes out, but that is not the reason we are doing it.
-- Richard Feynman

That's something of a quibble-- I can measure c by measuring a distance and a time to get there, but am I measuring two things or one? One number is convention, the other is physics-- same for mu and epsilon.
I don't think any of us are really disagreeing here. What I'd like to see is a nice summary of the current state of the number of free "physical parameters" in the universe, all expressed as unitless constants (like alpha=e²/hc), not a list of how many things can be set to 1. Personally, I don't see the point in setting constants that have units to 1, that's no better than choosing arbitrary units. The best way to eliminate constants (other than unitless ones) from equations is to embed them into the variables, not to set them to 1. There is a subtle difference.

I know as much about this as your average person in the street , I'm just trying to visual what time Is and not just sense the passing of it ( or distance of it or whatever..)

Does mass energy slow the velocity of real time so the passage of time is noticable -- relative to the mass energy?

if so would it be fair ask it in this way

Does mass energy slow the velocity of energy so the passage of energy/time is noticable -relative to the mass energy?

Is that anywhere near right or am I a clog out?

I'm not touching that edit button
I missed a 'to' out of the below sentence, it should have been phrased....
'If so would it be fair to ask it in this way

and I missed the word calculable.. so it should read 'noticable/calculable' on both occasions

It's not really clear what you mean by this question, but it seems to me that this is not a good way to look at it. For example, if mass-energy slowed the "velocity of energy/time", then more mass-energy should slow it more. Thus if I'm standing on the Earth, I should perceive time differently than if I'm in deep space, or near a black hole. None of those appear to be true-- relativity tells us that we always perceive time the same way, regardless of our surroundings. (The appearance of a hungry lion might appear to slow time, but that's just because our brains start analyzing more data and using more energy, so it's not a change in time it's a change in our brains.)

Basically, what time means is that the rate of all local processes is the same, so can all be characterized by a local clock. By "the same", I mean that the ratio of the rate of any process to any other is always the same for any observer who is in the same place as the processes, no matter what the observer is doing or how much mass-energy is nearby. So if I'm holding an unstable isotope in my hand, it has a certain half-life, relative to my own lifetime-- and nothing I do that does not directly change my lifetime (like killing myself) or the half-life (like bathing it in high-energy particles) will alter that comparison. That's time, in a nutshell.

I only ask these questions to help me understand and visualise it, I fully expect to be wrong. - I keep half expecting a rule 19 suddenly appearing under the heading - low intelligence posting - (admitting & accepting my lack of knowledge on the subject )

I fully understand what your saying as I'm burning of energy at a rate of knots

I thought that's what it was happening -relative to the mass energy anyway
does energy/time/c, (I hope it's ok to call it that, it assists me in visualising whatever time is) not run slower on say Jupiter with a larger mass energy than Earth with smaller mass energy & at the point of inifite mass stop all together.. or is that the wrong way to look at it...
i,m taking space/time energy as a one with mass energy.. If we took a timeline of pure energy at a volocity of 300.000kms and on the way something caused it to turn into mass energy, would that mass energy not slow the energy/time radius for a certain distance from it's central point,[could the energy timeline which is being created on the fly still carry on at velocity c] thus allowing the mass energy to recognize the existence of time and be calculable relative to itself and size...

I'll understand if I just get a reply stating 'NO!'

Time does not run slower near Jupiter, or near a black hole-- it runs at the normal rate for time. When people say "time runs slow near a black hole", it is a terrible misnomer-- what they really mean is that an observer far from the black hole will infer that time is running slow near the black hole, but they cannot perceive that time-- to do that, you'd have to be where the time is that you are talking about, and there time runs normally! Relativity is not about what happens to local observers, it is about translating from the local observer's perceptions (which are always perfectly normal) to the point of view of some other observer.

ok I understand what you are saying about time being relative
If we took two people- one on jupiter and one on Earth. From both reference points time would be running normaly -it's only when they communicate together that they recognise the time difference... and they would find that for the person on Jupiter time is running slower...
......
When they talk about the 4th dimension of time is that seperate from space-time or is it the same thing?

Space-time is 4 dimensional. The first three dimensions are space(length, width and height), the 4th dimension IS time.

Right, it's like two people reading a book describing a historical incident. One might be a faster reader, but that doesn't mean they think the events they are reading about happened any faster.

Just to be sure I understand things correctly, the Twins Paradox does end up with the twin that made the relativistic journey experiencing less time between departure and return than the twin that stayed at home, doesn't it? So they do actually experience time at different rates and we can say the moving twins clock runs slower (when we compare their ages at the end), can't we?

So can we say that a clock on Jupiter runs slower than a clock on Earth? But when you are on Jupiter, you don't notice the clock running slower, you would just be experiencing less seconds overall? Say we put a clock on a spaceship and sent it to Jupiter, left it there for a few years and then brought it back. After calculating out any time-dilation caused by the journey itself, would we calculate that the clock had been running slower while it was "at" Jupiter?

Yes. You can also say that the clock on Earth runs fast, and the Jupiter clock making a trip there would come back with its time a little ahead.

Either way, the time dilation of the trip there and back would also have to be taken into account.


Edit: And the gravity and movement of the Sun, the Galaxy, the Local Cluster, etc.

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Thanks!

It is true that the twins experience different total time intervals, but why do you say that they experience time at different rates? You are assuming that the total time intervals are somehow the same, so if they experience different elapsed times it must mean they experience time at different rates. I would instead say that they experience time at the same rate, but that the total time interval is different on the two different trajectories.

It is certainly often said just like that, but the statement can be confusing. The flow of time is no different on Jupiter for observers on Jupiter, it is rather the way time on Jupiter is conceived of from Earth that is slow. Getting back to the book analogy, imagine a story that is intended to unfold in "real time" by someone of average reading speed. Now imagine that same story is read by a very fast and a very slow reader. They will perceive time as flowing at different rates in the story as they read it, yet they both know how to translate that into an actual rate of events for the characters in the story. Would the slow reader say that the book character's time was running slowly? We could say that, but it would lend itself to the same confusion as here.

Yes, you would not notice anything strange-- you are the character in the story in that case.

We could as easily simply say that the clock was running normally all the time-- but less time elapsed. There the analogy would be to hand two different stories to a fast reader and a slow reader-- where the slow reader has several pages ripped out of the story, it is a shorter story, yet both stories begin and end at the same events, both readers start and finish the stories at the same time, and the flow of time for the characters in the story was just the same, one version just had less happen. The longer story is the clock on Earth, the shorter the clock on Jupiter. It is the same with the twin paradox.

Let me ask...because it is an interesting concept to think time is not constant at 2 separate locations. To stay with the current example of Jupiter and earth...let's say an astronaut on Jupiter works an 8 hour shift. At the very same time that the astronaut on Jupiter starts his shift, a newspaper delivery boy on earth starts his 8 hour shift.

When the delivery boy on earth's shift ends (8 hours exactly), then the astronaut on Jupiter will still be working?

I don't know the time differences between the two planets, but if its small then use another example with larger difference.

Time is constant, it just looks different when seen from another part of it.

The Earth worker and the Jupiter worker will both put in exactly eight hours. The Earth kid will see the Jupiter kid appear very slightly slower, but the Jupiter kid will experience eight hours as eight hours. And if the Earth kid goes to Jupiter, the difference in time will slowly even out to nothing the closer he gets to Jupiter's time-frame. Or vice versa, if the Jupiter kid goes to Earth. Frames are just differences in energy, whether it's motion or gravity.

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"If this were play'd upon a stage now, I could condemn it as an improbable fiction."
Shakespeare, Twelfth Night
"The Mayan symbol for "book" looks a lot like a triple hamburger, but I've never seen them claiming it as proof the Mayans had Big Macs." - KaiYeves
"Distance doesn’t matter much in space, where if you just start a thing off with the right kind of shove, sooner or later it will get where you want it to go." -Frederik Pohl, Mining the Oort

Yes, they will both agree that is they use the normal convention for what "now" means, if they start work at the same "now", the Jupiter worker will continue working past the "now" when the Earth worker gets off. But they will both work 8 hours. You just have to get away from the idea that a time interval is an absolute thing. If I told you that two cars built at the same factory at the same moment are found to have the same odometer readings when their clocks read a year later, would you expect that we have to be talking about two cars in the same location? So why should we expect that we have to be talking about two cars at the same moment in time?

You just posted a reasonable criticism of my explanation in another
thread. Lemme see if I can do the same for you here.

The confusion you introduce with the analogy is greater than the
confusion you were trying to avoid, in my opinion. There can be no
pages torn out of the book because there are no gaps in the Jupiter
observer's experience.

If, instead of reading a book-- or two slightly different books-- they
are watching a Big-Screen movie, projected on a sheet stretched
over the bowl of the Big Dipper, they will both see all the frames of
the movie, not missing anything, but the one who stayed at Jupiter
for awhile during the movie (A Russian movie made in the Soviet era,
obviously) will see it in less time than the one who stayed on Earth.
The two simultaneously see the movie start and simultaneously see
it end, but in between the traveller to Jupiter sees it speeded up a
bit, on average.

Can you do something with that analogy?

-- Jeff, in Minneapolis

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"I find astronomy very interesting, but I wouldn't if I thought we
were just going to sit here and look." -- "Van Rijn"

"The other planets? Well, they just happen to be there, but the
point of rockets is to explore them!" -- Kai Yeves

With the "ripping out pages", I did not mean to imply there were "gaps", merely that there is less time for things to happen for the Jupiter observer. A better analogy would have simply stated that the Jupiter story is simply shorter by a few pages-- but not that the stories are the same except for some gaps.

Let's look at the "twin paradox" from that perspective. The stories of the two twins begin at the same event (the deparature) and end at the same event (the return), but in between they are different stories and one is just longer than the other. It's not that one's "time was running slower", but rather, it's just a shorter story that had time running normally and still managed to link the beginning and end of the longer story of the other twin. This is what you are free to do once you let go of the concept of "absolute time", whereas saying "time was running shorter" fails to make that clean break.

But that's just it-- it's not the same movie, the two observers are experiencing different movies. If you are having them watch some third movie, then of course you will need to include light time-of-flight effects, but if there is no light, you don't need to concern yourself with that.
Again, that implies it is the same movie, but it is not-- one observer's movie is really shorter, as less can happen in it. Don't get me wrong, it is very standard to say that each observer perceives a certain amount of time, and a different amount of time elapsed for the other in that time for the one, so it is often said that the rate of flow of time was different. I'm merely pointing out that this nomenclature exposes an unnecessary bias that I feel actually undercuts the understanding of relativity: namely that if two observers are watching two different movies that start and end at the same point in space and time, and more happens in one movie than the other, that this means time was faster in that movie. I say, no, the movie was just longer-- yet still started and ended at the same times as the other. Why would they need to represent the same time elapsed? That's extrapolating one observer's time onto the other, which I claim is simply the last vestige of "absolute time" thinking-- we need to get away from that.

My understanding was that this sort of question is meaningless, in a way. It assumes that there is a universal time that applies to everyone everywhere, in the same way. But relativity denies this.

We can't say what the astronaut is doing when the delivery boy's shift ends. The delivery boy can only investigate that indirectly, by observing (through a telescope, say) the light emitted by the astronaut from far away. But this light will be subject to all sorts of counterintuitive relativistic effects.

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Correct me if I'm wrong but don't Einstein's theories and particle-wave duality go hand in hand. You can't argue against Einstein's theory by saying that a photon is either/or. They kind of explain and support each other don't they?

Well there exually are things that travel faster than the speed of light, eg phase velocity. But information (group velocity) cannot go faster than the speed of light.
See also:
http://en.wikipedia.org/wiki/Phase_velocity

The other option is the that there is no limit to the speed of information. Thus infinite. Things that are infinite give me always headaches.
I think the value of the speed of information is related to the things we can measure with it.

Thomas

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Why not just go with the idea of riding a wave. But in this case you are riding a light-wave.


(for the "character in the story")
A minute would be a minute. But you have traveled vastly farther than the ocean wave.

We can't say that in an absolute way, you're right, but we can say that from the point of view of a particular observer. So it should have been stated, "what the astronaut was doing, from the point of view of the delivery boy, when the delivery boy's shift ends". And the answer to that will be, still working. Note also that it will make a difference if the astronaut is in free fall, or in orbit, or hovering stationary above the planet, so one really has to work it out to see how the times match up. All I'm saying here is that if you pick one observer, and ask how much time elapses for that observer between two global "nows" conceptualized by that observer, it will not be the same as the time interval connecting those events for some other observer-- and because of some precisely arranged combination of time dilation and the use of a different global concept of what "now" means, the same physics will work for everyone.

Another time dilation analgoy, perhaps, would be the arrival time difference between two aircraft flying from New York to London, and flying at the same speed. Plotting both flights on a two dimensional Mercator projection would show the straight line path to be the quikest, yet it is not. Only when we invision the 3rd dimension do we see the advantage to a Great Circle route. The passengers in the straight line flight will assume more events will take place on the Great Circle flight as this greater distance would require more time, yet they would discover that the other flight would have arrived first. [If this is a good analogy, then I am sure I read it somewhere.]

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