# How could the infant universe have existed as a singularity?

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1. Dec 31, 2015

### R. E. Nettleton

A singularity is a region in which the curvature of space-time becomes infinite. But according to standard big bang models, at the initial point (at which T = 0) the pre-expansion space - as miniscule as it was - was filled uniformly with all energy that ever existed or will exist. But if all energy were concentrated into a single point, and simultaneously at every point, how could there be curvature? There would be no gradation of distortion; all of space would be equally curved, and this is equivalent to there being no curvature. This contradicts the idea that the universe was born from a singularity.

Equally, what would this curvature be relative to? We can only say that a particular region is distorted because it deviates from the "natural", un-curved state of space-time. Would it not be nonsensical to say that space-time was curved (to an infinite degree) without there being something to compare this curvature to? It would be akin to stating that the universe is rotating to an infinite rate ... relative to what? All frames of reference exist inside that initial, perhaps infinitely small point, and if the entirety of this point is curved to the same degree, how could one say that it is curved at all?

2. Dec 31, 2015

### Orodruin

Staff Emeritus
You are missing some fundamental concepts of GR. To start with, the singularity in FRW solutions is not really part of the space-time, but the space-time is not geodesic complete. Second, energy is generally not conserved in FRW space-times, there is no time translation invariance. Third, you seem to be talking about the curvature of space, not the curvature of space-time, these are not the same thing.

3. Dec 31, 2015

### mathman

The state of the universe at T=0 is an open question. Big bang theory is about what happened afterwards.

4. Dec 31, 2015

### phinds

... which is why it is considered mathematical and not physical. "Singularity" in physics really means "the place where the model breaks down and we don't know WHAT was/is going on.

5. Dec 31, 2015

### marcus

That is right in a sense, it is a region where a specific model fails and we have to stop relying on that particular model. But there may be improved models we can switch over to at that point that do NOT fail.

In the past there have been singularities (failures, glitches, breakdowns) in other physical models and they have been fixed---by modifying the theory or by quantizing it. The thermal radiation curve had a singularity which Max Planck fixed in year 1900. It was an infinity-type singularity--the curve blew up. It was called "the ultraviolet catastrophe". Planck fixed the curve so it did not have the singularity---this was the birth of quantum mechanics---especially when Einstein drew some conclusions in 1905 from how Planck fixed it.

Singularities are not something in Nature. They are symptoms of a manmade theory needing to be fixed. Theories evolve over time so as to expand their domains of applicability and eliminate singularities. We may be in a period in Cosmology analogous to how it was with radiant heat theory in 1900.
At cosmology conferences you get presentation and discussion of various NON-SINGULAR cosmic models people are trying out. Often nowadays they are BOUNCE models---this is currently a popular line of investigation. Who knows? Maybe that way of fixing the cosmic glitch will work out

6. Jan 1, 2016

### Loren

Well said.

In the end, theories are simply a set tools that allow us to do work in the domain of physics, much like the assortment of tools in a mechanic's toolbox.

7. Jan 1, 2016

### OCR

Thank you, thank you, thank you!! ...