Hace días una persona random me escribió para preguntarme sobre si tiene sentido físico la predicción de la teoría del #BigCrunch la cual dice que el universo podría colapsar y alcanzar una densidad infinita. Pedí ayuda a un par de amigas cosmólogas y como la respuesta conjunta quedó bonita la dejo por aquí:
Una densidad de energia infinita a tiempo finito no es física. En ese punto tenemos una singularidad. Quiere decir que perdemos predictibilidad en la teoría, es decir, que nuestra teoría allí no es válida y no sabemos decir que es lo que pasa.
The question of whether the universe is “open” or “closed” is of great interest. Current observations seem to indicate that the metric expansion of space is accelerating, i.e., the expansion is speeding up, so all the matter in the universe will never be able to come together in a big crunch. However, that view can always change as more observations are made.
My thoughts on a big crunch, if it was possible, is that it would only involve matter coming together, not the whole universe. Even if all the matter came together in a giant singularity, the metric of space around it would continue to expand, because the expansion of the universe is not just all the clumps of matter moving away from each other in space, but it is the metric of space itself that is expanding.
Just like when a galaxy forms by matter coming together via gravity, that does not mean that the metric of space is contracting. It means that all those stars and other matter are moving through space to come together as a galaxy. The metric of the space that that matter is moving through, is still expanding. It’s just that gravity, the curvature of spacetime around the matter is causing matter to move together faster than the metric expansion is expanding.
So I don’t think the universe itself will collapse, but maybe all of the matter in it could (if future observations indicate that that is possible.) Although I could be completely misinterpreting those theories.
#2that x2
Also, regarding infinite time so that infinite density could exist…
Because the curvature of spacetime around matter causes time to slow down (for an observer in another reference frame), as the density increases, the time would slow down. So time would approach infinity as density approached infinity and perhaps this would allow for the singularity to exist (or to continuously form).
La conclusión del Big Crunch de que si el universo tiene una densidad crítica se contraería es una conclusión física.
Lo que no es física es la predicción de que se contrae todo a un punto tal que la densidade de energia llega a infinito (en un tiempo finito).