Why is the speed of light?

exponent137

I think that Duff's idea is creative, but he tried to much.

1. I think that Planck's mass is dimensionful also at Planck's units.
2. I think that it is statistically much more possible that Planck's mass is increased by factor 0.2 instead that all particle masses are increased by factor 5.
3. We peoples think in units. We feel consciousness, so time, (and mass, lenght etc) not only dimensionless things. Okun say in trialogue that he wrote in word (some sort of units) not only in formulas and equations.
4. time is mathematicaly different that lenght. It is not symmetric etc.

rbj

well, it's not just Duff. Frank Wilczek said in http://www.physicstoday.org/pt/vol-54/iss-6/p12.html June 2001 Physics Today
If you measure every physical quantity, and refer to everything in terms of Planck units (and there is nothing that says we cannot do that), then there simply is no G or c left to vary. and when you take every physical quantity and express it in terms of or relative to its corresponding Planck unit, that is dividing by the Planck unit, if you do that there are no dimensions applied to those quantities. in such a context, when you talk about the mass of some particle, [itex]m_i[/itex], you are really referring to the ratio of that mass to the Planck mass or

[tex] \mu_i = \frac{m_i}{m_P} = \frac{m_i}{ \sqrt{ \frac{\hbar c}{G} } } [/tex]

which is dimensionless.

so you say this dimensionful quantity G varies because of some experiment that measures G in terms of some objects in the experiment that had properties that are dimensionless numbers multiplying these predefined definitions of a unit mass, unit length, and unit time (which are defined in terms of some prototype or kind of prototype properties such as Cesium). and what i would say instead is the ratio of these properties to their corresponding Planck units is what really varied. and it is these ratios that are the salient numbers.

while i agree with you that mass is different "stuff" than is time or length or electric charge, when you are in Planck units, the Planck mass is just the number 1. and the Planck time is just the number 1 as is the Planck length. but when you refer to these same quantities, in terms of other units, then because those other units have an anthropometric definition that is independent of Planck units, then, in terms of those units, the Planck mass or Planck length or Planck time are not dimensionless.

exponent137

Wilczek's article (I think, I need to read it again after few years) does not touch dimensionless mpl, lpl and tpl. I think that this is the main problem of duff's ideas.


So my article and Okun's article (in trialogue) are in contradiction to Wilczek's article.

Other will follows.
regards

rbj

lessee, the title of the Wilczek article that i referred to is something like "Scaling Mount Planck". i think that it obviously has something to do with m_P, l_P and t_P (the base Planck units). i think he makes and supports the same point of Duff (and Barrow quoted below), that it is the dimensionless quantities that matter. We measure time, length, and mass against some like-dimensioned standards. We do not measure anything without such comparison.

again, i am saying m_P is only as dimensionless as any other mass. if you are expressing a mass m in terms of the Planck mass as m/m_P, that is a dimensionless value. and the Planck mass expressed as such is the dimensionless 1.

i'm more confident of what Wilczek and Duff and John Barrow and John Baez (and practically any other physicist that has written about this on some blog) say about this than what you are saying about it. much more confident.

from Barrow:

[An] important lesson we learn from the way that pure numbers like α define the world is what it really means for worlds to be different. The pure number we call the fine structure constant and denote by α is a combination of the electron charge, e, the speed of light, c, and Planck's constant, h. At first we might be tempted to think that a world in which the speed of light was slower would be a different world. But this would be a mistake. If c, h, and e were all changed so that the values they have in metric (or any other) units were different when we looked them up in our tables of physical constants, but the value of α remained the same, this new world would be observationally indistinguishable from our world. The only thing that counts in the definition of worlds are the values of the dimensionless constants of Nature. If all masses were doubled in value [including the Planck mass m_P] you cannot tell because all the pure numbers defined by the ratios of any pair of masses are unchanged.


Barrow does not include G in that, but the principle is the same. It's the dimensionless quantities that we measure and even perceive. Our perception of length is normalized to the ballpark size of us. Our perception of quantities of time has something to do with how fast we think. Our perception of mass is in comparison to the masses of things we commonly deal with which is in the same ballpark as the masses of us.

It's only the dimensionless parameters of the universe (there are currently thought to be 26 of them) that ultimately matter. variation of the dimensionful parameters (like G or c or h or e) are all conflated with whatever anthropometric units we choose to think of such parameters in terms of. the only way to remove such parochial anthropometric dependence is to express all such quantities in terms of some defined "Natural units". when you do that, the expressions of such mass, time, or length, are dimensionless.

birulami

Consider one of the very first computer games, http://en.wikipedia.org/wiki/Pong. I don't really know whether the "ball" had a fixed speed or could go faster too, but just consider it always had a fixed speed. Now you are trapped in the 2D world of Pong and want to build a clock. What comes to mind in this confined world is to count how often the ball goes back and forth. Nice clock. Now you start measuring the speed by looking at how far the ball goes within N clock ticks. Sounds silly? Bear with me a moment longer.

The next version of the game allows the outside players to change the speed of the ball. But you keep measuring speed with your click clicks. Would you notice a change of speed. Of course not. During N clock clicks, the ball still goes the same distance. For you the speed did not change.

What has this to do with your question? Just think of how the most accurate clocks are made. They rely on electromagnetic oszillations, as far as I know, exactly what light is too. So if light would slow down or speed up (for whatever reason), your clocks would likely suffer the same influence and slow down or speed up respectively. Consequently you would not be able to measure a change in the speed of light. And don't think you might 'feel' it. Your whole body chemistry relies on the same electromagnetic phenomena, so it would slow down or speed up in sync.

Personally I believe that this is exactly what special relativity describes with regard to time.-)

Harald.

gilowoskian

Ok so i was wondering. If it were possible to travel faster then the speed of light wouldn't you just disappear, and if this was true couldn't there be things out there that travel faster then light but we just cant see them to know they exists?

cristo

It is impossible for a body with mass to travel at, or faster than, the speed of light.

Chronos

Tachyons are entities theorized to travel at superluminal velocites. They are permitted to travel at any speed greater than c, but never equal to or less than c [pretty weird].

Dick

Good news. You can have tachyons in various versions of string theory. Bad news, if you have a tachyon, it means you have a PROBLEM. You'd better get rid of it somehow.