# A poll

## Is the idea "It's all unitary anyway" ever comforting to you?

22.2%

55.6%
3. ### What?

22.2%
1. Jun 29, 2007

### pervect

Staff Emeritus
When unpleasant things happen, do you ever comfort yourself by saying "It's all unitary anyway..."

2. Jun 29, 2007

### Fra

> "It's all unitary anyway..."

Is it? :)

/Fredrik

3. Jun 29, 2007

### pervect

Staff Emeritus
Well, according to standard quantum mechanics it is, also QFT. Unitarity implies reversibility (unitary transformations are invertible), and also that no information is ever "lost".

There is perhaps some doubt about whether quantum gravity is unitary, last I heard though Hawking had joined the "no information loss" camp.

4. Jun 29, 2007

### turbo

No. Existence may be a zero-sum game at some level, but we as humans do not exist/perceive at that level.

5. Jun 29, 2007

### Proof.Beh

Is except it?

Thanks.
Mr Beh

Last edited: Jun 29, 2007
6. Jun 29, 2007

### samalkhaiat

Why not antiunitary?

In QFT, time reversal transformation is generated by the antiunitary operator;

$$\mathcal{T} \phi (x,t) \mathcal{T}^{-1} = \eta_{T} \phi (x,-t)$$

So is any non-singular transformation!

All depends on the vacuum; whether it is true or fulse vacuum!!

sam

7. Jun 30, 2007

### Fra

The way I see it, unitarity is more often than not, the best single guess, but it's not the only option. There mere uncertainty alone implies that to think that there is a fixed unitarity can hardly be true in the general case. But of course in many special cases.

It's not a coincidence though that theories almost be defintion, apply to "special cases".

In my thinking I don't think of special theories, I think of something as close to the general case my small mind can grasp, and I can't accept unitarity as a fundamental thing. Technically, it would IMO be exepctations. But since these expectations are often well supported, they appear to be alost fundamental. But the different in the viewpoints is on the edge of the theories evolution. I have at least, hard to understand a fundamentally evolutionary model without non-unitary behaviour. In my thinking the non-unitary behaviour is even part of the key.

/Fredrik

8. Jun 30, 2007

### Fra

As long as the non-unitary information part is small in relative significance, it's not a problem IMO. But the non-unitary isn't fundamental either of course. Typically the implication of learning is a desired to inflate the models to make it more unitary.

/Fredrik