Absorber Theory of Radiation

[Rayaan]

This is a theory of radiation put forward by Wheeler and Feynman in 1945 which says that radiation can also flow backward into space in such a manner as to arrive back into the source (or the emitter) if the expansion of the universe begins to reverse. These backward-moving radiation are called "advanced waves" whereas the ordinary radiations are called "retarded waves."

Do any of you physics people know anything about this? Is it really possible that stars can absorb their own light if the universe ever begins to contract?

Edit: Here's a quote from a book entitled "The Mind of God" in relation to this topic:

We never observe organized patterns of radio waves coming from the edges of the universe and converging onto radio antennae. (The technical term for outflowing waves is "retarded," whereas outflowing waves are "advanced"). If, however, the arrow of time were to reverse in the contracting phase of the universe, then the direction of radio-wave motion would also have to reverse - retarded waves would be replaced by advanced waves. In the context of Wheeler’s 'turning of the tide', this would suggest that close to the big bang all radio waves would be retarded; then, as the maximum expansion was approached, so increasing amounts of advanced waves would occur. At maximum, there would be equal advanced and retarded waves, whereas during the contracting phase advanced waves would dominate. (Davies, 54).

[orogenicman]

This is a theory of radiation put forward by Wheeler and Feynman in 1945 which says that radiation can also flow backward into space in such a manner as to arrive back into the source (or the emitter) if the expansion of the universe begins to reverse. These backward-moving radiation are called "advanced waves" whereas the ordinary radiations are called "retarded waves."

Do any of you physics people know anything about this? Is it really possible that stars can absorb their own light if the universe ever begins to contract?

I think the finding that the universe is not only expanding, but that said expansion is accelerating makes the contraction hypothesis problematic, at best.

[theVOID]

In that hypothesis when space contracts time also goes backwards, so if that scenario were true then yes, it would "absorb" the radiation it once emitted.

[KichigaiNeko]

Not that I know physics well (if at all) rayaan but I would think that that theory was just a 'thought experiment' who knows what is going to happen...the universe IS a strange and wondrous thing...as any physicist will tell you

[LEDO]

When space contracts, time will not go backwards. This would violate the second law of thermodynamics. The universe increases in entropy. Radiation is emitted from a source because that source is unstable in its current state. The natural tendency is to go to a ground stable state. Any object can absorb radiation and become unstable, but the idea of it somehow flow back toward its source is well, retarded. Don't any of you guys read Hawkins?

[KichigaiNeko]

When space contracts, time will not go backwards. This would violate the second law of thermodynamics. The universe increases in entropy. Radiation is emitted from a source because that source is unstable in its current state. The natural tendency is to go to a ground stable state. Any object can absorb radiation and become unstable, but the idea of it somehow flow back toward its source is well, retarded. Don't any of you guys read Hawkins?

Yes I do ...hence the "thought experiment" note

[Welsh cake]

When space contracts, time will not go backwards. This would violate the second law of thermodynamics. The universe increases in entropy.

Time would start to slow down if the universe contracts, correct?

[LEDO]

When space contracts, time will not go backwards. This would violate the second law of thermodynamics. The universe increases in entropy.

Time would start to slow down if the universe contracts, correct?

I believe that is correct.

[Anomalocaris]

According to relativity rate of flow of time only changes between different frames of reference. Relative to what frame of reference does time slow down or reverse when the entire universe contracts?

[lilphil1989]

When space contracts, time will not go backwards. This would violate the second law of thermodynamics. The universe increases in entropy.

Time would start to slow down if the universe contracts, correct?

I believe that is correct.

What make you guys believe that?

This is a theory of radiation put forward by Wheeler and Feynman in 1945 which says that radiation can also flow backward into space in such a manner as to arrive back into the source (or the emitter) if the expansion of the universe begins to reverse.

Not quite, actually absorber theory says nothing about the expansion of the universe. Advanced and retarded potentials are general objects in physics, not specifically related to absorber theory.

Absorber theory is a way to try to re-cast radiation theory in a way that's invariant under time-reversal. Usually when you solve the Maxwell equations for some accelerating charge, you get two solutions, one which is a function of (x - ct) and one of (x + ct). Usually, the latter is disregarded as it is considered non-causal. Doing that, however, seems to breaks the time-reversal symmetry, so Feynman and Wheeler were looking for a way to build a theory in which you don't have to arbitrarily discard a solution.

It works, and you get sensible solutions, if you impose the condition that the retarded and advanced fields are equal at every spacetime point. It isn't necessary though, from the viewpoint of calculating things you get the same answers just using retarded fields. It does make the theory look nicer because you don't have to give privilege a priori to the retarded fields.


The real influence of this idea is that it was working on this that prompted Feynman to come up with the formulation of quantum mechanics using path integrals and starting from a Lagrangian (kinetic - potential energy) instead of a Hamiltonian (kinetic + potential energy), which is the way that almost all work in quantum field theory for particle physics is done these days.