- #1

Drakkith

Staff Emeritus

Science Advisor

- 21,299

- 5,145

You are using an out of date browser. It may not display this or other websites correctly.

You should upgrade or use an alternative browser.

You should upgrade or use an alternative browser.

- Thread starter Drakkith
- Start date

- #1

Drakkith

Staff Emeritus

Science Advisor

- 21,299

- 5,145

- #2

bapowell

Science Advisor

- 2,243

- 259

- #3

Chalnoth

Science Advisor

- 6,197

- 447

If you take the big bang theory seriously, its size would have been identically zero. That's what the singularity means. And that's why it's nonsense.

In order to get an answer different from zero, you have to make use of another model, such as inflation or the LQC bounce.

- #4

Drakkith

Staff Emeritus

Science Advisor

- 21,299

- 5,145

If you take the big bang theory seriously, its size would have been identically zero. That's what the singularity means. And that's why it's nonsense.

In order to get an answer different from zero, you have to make use of another model, such as inflation or the LQC bounce.

Take the radius of the current observable universe. As we look backwards in time, this radius shrinks. I was under the impression that at t=0 this radius is not zero and that the singularity doesn't come from computing the radius/volume of the universe, but from something else in the math. Is that incorrect?

- #5

Chalnoth

Science Advisor

- 6,197

- 447

The scale factor at that point goes to zero. You can't say that the entire universe was a single point, because the classic big bang universe is infinite, and infinity multiplied by zero is indefinite. But because the observable universe is finite, its size would have been zero when the scale factor reaches zero.Take the radius of the current observable universe. As we look backwards in time, this radius shrinks. I was under the impression that at t=0 this radius is not zero and that the singularity doesn't come from computing the radius/volume of the universe, but from something else in the math. Is that incorrect?

Of course, in an inflationary or other more sophisticated model, the scale factor would not have been zero at that point in time. Exactly how big it would have been is highly dependent upon the specific model, though it had to be quite tiny. With inflation, for example, it depends upon the energy scale of inflation.

- #6

Drakkith

Staff Emeritus

Science Advisor

- 21,299

- 5,145

I see. Thanks for clearing that up!

- #7

Chronos

Science Advisor

Gold Member

- 11,429

- 743

- #8

Drakkith

Staff Emeritus

Science Advisor

- 21,299

- 5,145

I'm not sure I understand. The observable portion of the universe is always finite. What does the issue of whether or not the entire universe is infinite have to do with this?

- #9

Chronos

Science Advisor

Gold Member

- 11,429

- 743

Share:

- Replies
- 15

- Views
- 9K