Is SR-allowable time travel future-only ?

[kg4pae]

Ah, perhaps here I can help. A negative mass in physics COULD be achieved as a local imbalance in the ergoregion of a BH. Think of a really REALLY extreme Casimir setup. That said, we're talking about a QM/GR theory around a GR object that may or may not exist and 'live' as described by the math, so who knows?

I was wondering if you could post details about this. I'm interested and have never heard of negative mass existing anywhere.

 

[Frame Dragger]

I was wondering if you could post details about this. I'm interested and have never heard of negative mass existing anywhere.

For a total negative Komar Mass: http://www.iop.org/EJ/article/0264-9381/23/24/L01/cqg6_24_l01.pdf?request-id=b2ceed1b-e7eb-4edb-b801-d0ecd3739f7c

The other issue is the that counterrotating particles in the ergoregion will have negative energy, causing regions of 'imbalance' in line with QM. It's a central feature of rotating BHs. Everything from Wikipedia onward will have info for you. As far as I know, the issue is negative MASS, in the form of negative energy. Kerr BHs are the models for this.

EDIT: You said, "existing anywhere"... Well... to be fair everything I'm talking about is pure theory and conjecture. The ergoregion is math and theory and that's pretty much it right now.

EDIT2: Here's some more postage. http://adsabs.harvard.edu/full/1996MNRAS.282..580Y
Also, if you haven't already do some research on The Penrose Process for some more insight.

EDIT3: For the OP, sorry, I realize that this has 0% to do with SR.

 

[Altabeh]

Seeing how the topic of discussion is "Is SR-allowable time travel 'future only'?", we must be talking about the metric $$diag\left(-1,1,1,1\right)$$. Since this metric has no coordinate-values in it, automatically we can say that the Christoffel-symbols are zero, the Ricci-tensors are zero and thus the curvature is zero. If the curvature is anything but zero, we must be talking GR and thus must be careful not to overuse SR where it doesn't apply.

Pardon me, but what is this all about? Did we say something very strange to you that made you start giving away some fundamental things in the theory of Relativity?

Strictly speaking yes, but you have to be careful how you interpret it. Since

$$\gamma\equiv\frac{d t}{d \tau} = \frac{1}{\sqrt{1 - {\left(\frac{v}{c}\right)}^2}}$$

whether $$\gamma$$ (the rate at which observed time changes with respect to proper time) is positive or negative depends on how we choose the square root (in SR). Until now, the justification is that no experiment allows us to choose the negative square root and backward time-travel.

The mechanism of traveling backwards in time is not like this in SR! We talked about this earlier and said that it only comes from twin paradox and FTL scenario which in turn gives rise to the violation of causality! Not only experiment does not allow us to use

$$\gamma\equiv\frac{d t}{d \tau} = -\frac{1}{\sqrt{1 - {\left(\frac{v}{c}\right)}^2}}$$,

but also the theory itself does not let one use the negative sign because coordinate time and proper time are both either future-directed or past-directed.

[EDIT]: Suppose the time boost in Lorentz transformations. If we take a differential of it,

$$dt'=\gamma(dt-\frac{v}{c^2}dx)$$,

then obviously under a time inversion $$dt\rightarrow -dt$$, we have $$dt'\rightarrow -dt'$$ and thus $$dt dt'>0$$. So the proper time

$$\tau= \int_{t_0}^{t_1} {1/ \gamma} dt$$ changes sign under time inversion because of that dt in the integrand.

AB

 

[Altabeh]

For a total negative Komar Mass: http://www.iop.org/EJ/article/0264-9381/23/24/L01/cqg6_24_l01.pdf?request-id=b2ceed1b-e7eb-4edb-b801-d0ecd3739f7c

Very helpful!

AB

 

[Frame Dragger]

Very helpful!

AB

Glad to hear it. :)

 

[bcrowell]

I find that URL actually a bit pathetic in explaining tachyons. Since no material particle can go faster than the speed of light in a vacuum (cf above), the only real way to define tachyons is material particles that go faster than light in their medium. Such tachyons have been observed in nuclear reactors.

The WP article is correct and you're incorrect. The c in special relativity cannot be interpreted as the speed of light in a medium. Nobody uses the word "tachyon" to describe particles emitting Cherenkov radiation.

 

[Frame Dragger]

The WP article is correct and you're incorrect. The c in special relativity cannot be interpreted as the speed of light in a medium. Nobody uses the word "tachyon" to describe particles emitting Cherenkov radiation.

I love it... if this guy was correct there wouldn't BE any Čerenkov R!

kg4paep The famous 'blue glow' known as Čerenkov Radiation is a RESULT of normal particles experiencing the termination shock of one material's c into another. I'm curious how you think we'd be able to observe an FTL phenomena as a UV+ bandwidth emission? I can't even follow your train of thought here, sorry.