After some additional reading, I agree with you, Abd. Or perhaps I should just say that my assertions from last evening were false and I'm now even more confused you are.
Which I will take as step forward ... it is far better to be confused than to be wrong. Jeff On Fri, Dec 28, 2012 at 8:45 PM, Abd ul-Rahman Lomax <a...@lomaxdesign.com>wrote: > At 08:11 PM 12/28/2012, Jeff Berkowitz wrote: > >> I think a lot of the reasoning about photons, above, is wrong. The red >> shift has nothing to do with gravity, only the relative velocity of the >> photon source relative to the observer. >> > > Eek. Apparently not. > > > If an event just outside the event horizon of a black hole emits a >> photon, an observer at rest relative to the black hole will observe no red >> shift regardless the strength of the black hole's gravitational field. >> > > Apprently this is not so, and it directly contradicts many sources that > might be expected to get it right. The red shift is not a motion-related > doppler shift, it is a gravitational shift, purely. > > > If the observer then accelerates away from the black hole, similar >> photons emitted from the same source will appear to be red shifted. It's >> entirely an observational effect. There is no loss of energy from the >> photon and no need to store anything anywhere. >> > > This topic is a continual temptation to me to stick my foot in my mouth. > What I'm getting is that there is a lot I don't understand about black > holes and particularly about the event horizon. Essentially, I've felt that > I have a decent understanding of special relativity, but general relativity > is another animal, and gravitational effects on light are an aspect of > general relativity. > > The event horizon, it is being said, is the point at which no path exists > for the photon to escape, to travel away from the singularity. This is > caused by the intensity of the gravitational field, which is a fixed value > at the event horizon. That's the value that allows no escape. Just outide > the event horizon, the photon may escape, but does not escape unscathed. It > loses energy climbing the gravitational potential field. It red-shifts as > it loses energy. (That energy is being converted to potential energy, just > as with any object with momentum away from a gravity source loses momentum, > trading it for potential energy.) > > The puzzle to me here is the statement made that an object travelling > toward the black hole will not only be seen through a red shift, but will > also appear to slow, such that it never passes the event horizon, it just > gets closer, but more and more slowly, until it is red-shifted out of > observability. It is alleged that this takes forever. > > And I don't understand that. > > To resolve this, part of what I'll need to look at are the equations for > gravitational red shift, or the effect of gravity on light. > > Then I can look at what would happen with light emitted outside the event > horizon (which I presume will fall out of the gravitational equations), and > can construct a thought-experiment for an object approaching the event > horizon, which was the original problem here. > > It *looks* to me like some material that is popularly stated about black > holes and event horizons might be incorrect, but I certainly don't know > enough to claim that with any clarity. > > I *do* imagine that I know enough to deny that the red shift being talked > about here is the ordinary doppler shift, i.e., due to the relative > velocity between the source and the reference frame. >
