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tovisonnenberg
- 19
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How does the expansion of space cause light to lose energy?
That is not correct. In an expanding universe light emitted from a cosmologically remote point DOES lose energy as it travels and is red-shifted more and more, and loses energy more and more, as the point of reception is farther and farther away. There is no conservation of energy on cosmological scales.The light has not really changed energy.
Just to be clear, this refers specifically to the energy relative to comoving observers, an assumption that is not always stated explicitly. Energy is not an inherent property of a light signal by itself (the stress-energy tensor is). In that sense, the light has not changed energy, because energy is not a property inherently associated to it.That is not correct. In an expanding universe light emitted from a cosmologically remote point DOES lose energy as it travels and is red-shifted more and more, and loses energy more and more, as the point of reception is farther and farther away. There is no conservation of energy on cosmological scales.
This is missing a qualifying statement. The baseball does not have an inherent energy and momentum either - it only has a particular energy and momentum given some fixed frame. As we all know, energy and momentum are not Galilei invariant. They will take different values in different inertial frames and no frame can be said to be preferred over another.If someone throws a baseball from the back of moving pickup truck it will not be going very fast when you catch it. It would hit your glove hard if they threw it forwards and you caught it. The pitcher throws the ball with the same energy/momentum each time. It is only the measurement from your perspective that changes with each pitch.
Good point. Thank you for that clarification.Just to be clear, this refers specifically to the energy relative to comoving observers, an assumption that is not always stated explicitly. Energy is not an inherent property of a light signal by itself (the stress-energy tensor is). In that sense, the light has not changed energy, because energy is not a property inherently associated to it.
Inflation has no effect on CMB wavelength because it happened before the CMB was released. Do not confuse inflation with expansion. Expansion is the scale of the universe increasing with time, inflation is a hypothetical period of rapid expansion in the very beginning of the universe, before CMB, before nucleosynthesis, intended to explain (among other things) why the universe is so homogeneous.So, inflation itself has zero effect on (for example) CMB wavelength