- #1
martix
- 162
- 1
The following thought/problem recently hit me:
What the hell happens to photon energy lost due to the cosmological redshift?
What the hell happens to photon energy lost due to the cosmological redshift?
Chronos said:Redshifted photons are also time dilated. Their energy is conserved over time.
The recoil effect you're describing is an effect that exists, but is extremely small and has nothing to do with cosmological redshifts. For example, if we lived in a universe that was undergoing cosmological contraction (a closed universe headed toward a Big Crunch), then we would still have a tiny redshift effect due to the effect you describe, but it would be overwhelmed by a much larger cosmological blueshift. Note that your example involves flat spacetime. We all agree that energy is conserved in flat spacetime. That isn't the issue. The recoil effect you're analyzing also has nothing to do with the situation described in #7.cubzar said:When a ball is thrown on the train, the 'missing' energy goes into pushing the train and the thrower when the ball is thrown. Whilst photons have no rest mass, the do have momentum, and the energy lost when they are red-shifted is used to push whatever emitted them in the opposite direction to the direction in which the photons are moving.
bcrowell said:We all agree that energy is conserved in flat spacetime.
TrickyDicky said:What energy? How do you figure there is energy in a spacetime with no curvature (no gravity) and therefore vanishing stress-energy tensor? Not much to be conserved, right?
WannabeNewton said:I think the point is that since the minkowski metric admits a time - like killing vector field, the energy conservation just follows regardless.
TrickyDicky said:What energy? How do you figure there is energy in a spacetime with no curvature (no gravity) and therefore vanishing stress-energy tensor? Not much to be conserved, right?
The theory of universal expansion and the law of energy conservation are two fundamental principles of physics that are not directly related. The law of energy conservation states that energy cannot be created or destroyed, only transformed from one form to another. The theory of universal expansion, on the other hand, describes the expansion of the universe over time. While the law of energy conservation still holds true on a smaller scale, it does not apply to the overall expansion of the universe.
No, the expansion of the universe cannot be explained by energy conservation alone. While energy is conserved on a smaller scale, the expansion of the universe is driven by the force of dark energy, which is a mysterious force that counteracts the gravitational pull of matter in the universe. This force is not fully understood and does not follow the laws of energy conservation.
Yes, there is strong evidence to support the theory of universal expansion. One of the key pieces of evidence is the observed redshift of light from distant galaxies, which indicates that they are moving away from us. This is consistent with the idea of an expanding universe. Additionally, the cosmic microwave background radiation, which is leftover thermal radiation from the early universe, also supports the theory of universal expansion.
The concept of energy conservation does not directly apply to the expansion of the universe. As mentioned earlier, the expansion of the universe is driven by dark energy, which does not follow the laws of energy conservation. However, energy conservation does still play a role in the formation and evolution of galaxies and other structures within the universe.
It is currently unknown if the expansion of the universe can be reversed or stopped. The force of dark energy is currently accelerating the expansion of the universe, but it is possible that this force could change over time. However, it is also possible that the expansion will continue indefinitely. Further research and observations are needed to better understand the expansion of the universe and its potential future trajectory.