A lot of us would like to see some signs of general relativity breaking down under extreme conditions, since that would give clues to a more complete theory. It isn't at all a new realization that it must break down somewhere -- even in the 1960s era of black hole research it was understood that this must happen deep inside them (near the singularity if it isn't spinning, or near the inner event horizon if it is).
The main reason we have not yet seen signs of GR breaking down is because we are not yet able to test it precisely enough in a regime where we expect it to break down. It would have been exciting if we saw it break down close to black holes in LIGO or EHT observations, but nope! It is still very accurate in those conditions.
Wat, have you been watching the excellent History of Astronomy series on PBS? It is absolutely amazing! And the Planets series right after that. The graphics they show blow my mind! I was thinking of you guys while watching both. PBS quality is definitely way higher than any commercial TV network. Their news too- they had a scientist on who works with the UN who was talking about how our land management techniques and the overreliance on meat is destroying the environment- a new study came out about that recently? They said we have about 10-12 years to change our ways before the damage is irreparable.
And be sure to read this!https://journals.aps.org/prl/abstract/1 ... 123.041601
We may be a step closer to a theory of quantum gravity!
The new study — published in the journal Physical Review Letters — provides a solid theoretical framework to discuss modifications to the Unruh effect caused by the microstructure of space-time.
Eduardo Martin-Martinez, an assistant professor in Waterloo’s Department of Applied Mathematics, elaborates on the team’s work: “What we’ve done is analyzed the conditions to have Unruh effect and found that contrary to an extended belief in a big part of the community thermal response for particle detectors can happen without a thermal state.”
The team’s findings of importance because the Unruh effect exists in the boundary between quantum field theory and general relativity, and quantum gravity, which we are yet to understand.
“So, if someone wants to develop a theory of what’s going on beyond what we know of quantum field theory and relativity, they need to guarantee they satisfy the conditions we identify in their low energy limits.”
It predicts that an observer in a non-inertial reference frame — one that is accelerating — would observe photons and other particles in a seemingly empty space while another person who is inertial would see a vacuum in that same area.
In other words; a consequence of the Unruh effect is that the nature of a vacuum in the universe is dependant on the path taken through it.
As an analogy, consider a universe with a constant temperature of zero and in which, no heat arises from the effects of friction or kinetic energy contributions. A still thermometer would have its mercury-level sat permanently at zero.
But the Unruh effect posits that if that thermometer was waved from side-to-side, the temperature measured would no longer be zero. The temperature measured would be proportional to the acceleration that the thermometer undergoes.
Raúl Carballo-Rubio, a postdoctoral researcher at SISSA, Italy, explains further: “Inertial and accelerated observers do not agree on the meaning of ‘empty space.
“What an inertial observer carrying a particle detector identifies as a vacuum is not experienced as such by an observer accelerating through that same vacuum. The accelerated detector will find particles in thermal equilibrium, like a hot gas.”
He further explains that as a result of this, it is reasonable to expect that any new physics that modifies the structure of quantum field theory at short distances, would induce deviations from this law.