Starship Asterisk*

orin stepanek wrote:Hey Chris; I'll be 70 in June.

All my respect mucker.

mark

makc wrote:

neufer wrote:Folks in the 2001 rotating space station *WILL NOT* age as slowly as folks on earth simply because they feel 1g of "centrifugal force." Rather they will age just slightly slower than the folks in the center of the 2001 rotating space station due entirely to the special relativity "twin paradox effect." To age as slowly as the folks on earth the rotating space station would have to generate spin velocities comparable to the orbital motion itself.[/list]

yes that is what I had in mind... but "comparable to the orbital motion itself"? feels like too much.

We're maybe bending time simply by orbiting the Earth? and if we had a rotating space wheel we would be bending it also????

Orin

orin stepanek wrote: I often wondered why a photon moving at the speed of light doesn't run out of energy and simply die; or turn off so to speak. So if it travels across the universe and it had no time it would still be just born. No energy needed.??? Yet it is so easy to stop a beam of light.

You are not the only one to wonder about that. See http://en.wikipedia.org/wiki/Tired_light

canuck100 wrote:

orin stepanek wrote: I often wondered why a photon moving at the speed of light doesn't run out of energy and simply die; or turn off so to speak. So if it travels across the universe and it had no time it would still be just born. No energy needed.??? Yet it is so easy to stop a beam of light.

You are not the only one to wonder about that. See http://en.wikipedia.org/wiki/Tired_light

But pretty much nobody wonders about this anymore. Also from the above reference:

"Today, tired light is remembered mainly for historical interest, and almost no scientist accepts tired light as a viable explanation for Hubble's Law."

A much better answer (already given) is that there's no reason for a photon to lose energy just by traveling through a vacuum, because doing so doesn't use any energy. This shouldn't be a surprise; it's analogous to a moving object in classical mechanics, which also requires no energy to stay in uniform motion.

Chris Peterson wrote: "Today, tired light is remembered mainly for historical interest, and almost no scientist accepts tired light as a viable explanation for Hubble's Law."

Yes, the article makes this clear and gives the many reasons for this . . . I originally had the Law of Inertia (N's 1st law) but then thought how do you define inertia for a massless photon? Didn't want to go there . . . an analogy, yes.

canuck100 wrote:Yes, the article makes this clear and gives the many reasons for this . . . I originally had the Law of Inertia (N's 1st law) but then thought how do you define inertia for a massless photon? Didn't want to go there . . . an analogy, yes.

Inertia is a meaningless concept for a photon. The related concept here is momentum, which is something a photon has. How can a massless particle have momentum? Because only the classical definition of momentum is the product of mass and velocity (m * v). Quantum mechanics extends this definition to be the Planck constant divided by the wavelength. This basically just recognizes that mass and energy are equivalent, and while a photon is massless it certainly has finite energy. Thus, it has momentum and can transfer that momentum to objects it interacts with, losing energy in the process (for example, a solar sail).