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A photon with zero energy cannot exist for several reasons. Firstly if it has zero energy it cannot have any effect on anything and cannot be detected.Secondly it cannot fit into our universe which has a finite size because it has an infinite wavelength. like the casimir effect where photons longer than a particular wavelength canot exist in a cavity causig a negative pressure in that cavity against the vacuum energy.
This leads on to an interesting thought that I have had for some time on the assumption that gravitons or gavitomagnetic waves (which are in some ways similar to photons are mostly very low frequency compared with photons ie frequuiencies are measured in cycles per year(earth's orbit down to a few cycles per second for a binary neutron star assuming that the quantum enegy is plancks constant times the frequency the quanta are very low energy and there are lots of them.The motions of galaxies in clusters represent cycles per billion years or more and there may be a lower limit to the frequency of gravitions in the universe because they just cant fit in. Can this be the source of some form of modified dynamics for very low frequency gravitiational effects like MOND?
I was thinking about blue-shifted light at an event horizon when BING! - my mind did a flip & I thought of this litle poser.Can a lightwave be so red-shifted that it becomes a flat line? If so, what would be the effect?Would the lightsource have to be moving away at c? Or at infinite velocity? Would a photon have to have zero energy for its wave to be flat? Can a photon with zero energy exist?
It's interesting to note that although we can't see anything beyond the observable universe, as centered upon us, we can see regions within the observable universe where energy originating from beyond the observable universe must be present, so although this energy will be present and interacting within those regions, we shouldn't be able to detect it's presence or it's interactions. Hmm... might just be a timing issue...
Can a lightwave be so red-shifted that it becomes a flat line?
Quote from: DoctorBeaver on 23/05/2008 20:53:49Can a lightwave be so red-shifted that it becomes a flat line? More precisely, it would become a constant electric and magnetic field.
Quote from: lightarrow on 24/05/2008 20:51:03More precisely, it would become a constant electric and magnetic field.Alberto - can you explain that, please?
More precisely, it would become a constant electric and magnetic field.
You would see a signal with a frequency approaching zero frequency from a very distant object.
You can also measure a single frequency "instantaneously" by using a phase sensitive detector and a short delay line (less than one cycle at the frequency you wish to measure) you split the signal into two paths send one directly to the phase sensitive detector and one via the delay line to the phase sensitive detector. The phase difference is a measure of the frequency.
The microwave radiation remaining from the Big Bang comes from 'everywhere' so, even when we detect that, we are not not particularly looking just at the limits of visibility. I am still not sure whether the spectrum of this radiation is due to 'cooling', red shift, or both.
There is a bigger volume at great distances than there is close to us so you might expect more photons to arrive and dominate the received radiation.
It might just turn out that the red shifting mechanism produces just the same effect as the cooling.
This is a good 'un, isn't it?
Bigger volume could also mean that concentration of photons is diluted.
The aveage density could be getting less (in the simpler model) but, compared with here, it would be the same.
I am still not sure whether the spectrum of this radiation is due to 'cooling', red shift, or both.
Quote from: sophiecentaur on 28/05/2008 23:55:03I am still not sure whether the spectrum of this radiation is due to 'cooling', red shift, or both.I'm not sure how cooling could work - there needs to be somewhere cooler for the energy to go, although if the CBR is spreading into 'new' space the effect must be for there to be less energy per unit of volume - would this equate to cooling?
Can't help but wonder if the original poster wanted to know if light reverts back to matter after shifting x number of times.