# World line coordinate finiteness

If you trace two particles' world line backwards in time, according to current theory, both objects should converge at big bang.

Would both objects arrive there simultaneously?

Another way of asking the question:

Is there any evidence that supports the idea that new matter is "introduced" into the universe as a continuous stream, as opposed to everything coming from a singularity both in time and space?

The analogy would be from the inside of a black hole. For each particle in that singularity, they would all have a world line that starts at the same spacial coordinate, but the particles would not be "introduced" into the black hole simultaneously. You can argue that time stops having meaning in a black hole, but that's only true for an "outer observer" in my reasoning.

• It seems like the answer is in your first sentence. Both objects originated at the same point in "time". To address the second part: introducing new matter into the universe would violate the law of conservation of energy. You would of course be right to object that the big bang introduced new matter and energy into the universe, but that period in history is still not well understood - though many have, and still are, trying. Aug 27, 2014 at 17:09
• @hde226868 It depends on your perspective on the universe. I believe "our" universe is simply the center of a black hole in a much older and larger universe. New energy can certainly be introduced into such a "sub universe", without violating the law of conservation of energy. You can of course argue that I'm not talking about the "grand universe" then - but for all intents and purposes we can't exit this black hole I believe we're inside. Thus, for us it will be the universe. Aug 28, 2014 at 20:40
• I would argue that you're talking about fringe science and any statements to that effect would be off-topic. Aug 28, 2014 at 20:42
• Apologies; looking back, that sounded overly snarky. Aug 28, 2014 at 20:51
• @HDE226868 There are many observed effects that I believe can be explained by such a "sub universe". For example accelerating universal expansion, isotropy of cosmic background radiation, big freeze seems a natural consequence, Aug 28, 2014 at 22:19

Particles are generated and destroyed all the time. This is obvious for photons, but also holds for massive particles. Today most particles are stable and long-living, but shortly after the big bang the universe was so hot that particle generation and destruction were in some equlibrium and all particles participated in this process (for photons this continued until the epoch of re-ionisation at redshift $z\sim1000$. There is definitely no particle around today that existed all the time since $t=0$.