Ok stupid question, but I want to know if killing black holes are possible

[mikegarrison]

8 hours ago, kerbiloid said:

The Alcubierre drive needs it, not provides.

LOL! The perfect response to the Alcubierre drive.

[K^2]

9 hours ago, tomf said:

But it does in theory exist?

Edit: I only mentioned alcubierre because that is why I believe negative mass is theoretically possible.

It's a feature of General Relativity that it extends into negative energy densities. But nobody knows if that extension is physical or purely an artifact of mathematics used to describe it. There are plenty of similar examples. We frequently use imaginary amplitudes in electrodynamics, but you can't point an electric field along an imaginary axis. These solutions are not physical, but they are allowed by the mathematics of electrodynamics and can actually be useful as part of computation due to the superposition principle. General Relativity is non-linear, however, so if the energy density solutions aren't physical something new and exciting is going on there, but we just don't know at this point.

[magnemoe]

16 hours ago, K^2 said:

It's a feature of General Relativity that it extends into negative energy densities. But nobody knows if that extension is physical or purely an artifact of mathematics used to describe it. There are plenty of similar examples. We frequently use imaginary amplitudes in electrodynamics, but you can't point an electric field along an imaginary axis. These solutions are not physical, but they are allowed by the mathematics of electrodynamics and can actually be useful as part of computation due to the superposition principle. General Relativity is non-linear, however, so if the energy density solutions aren't physical something new and exciting is going on there, but we just don't know at this point.

Yes lots of stuff like this like tachyons, mathematical possible but unlikely to exist. 
Math is an abstract concept. How abstract: fill up two liter water, now remove 5 liter and you have -3 kg mass  repeat in real life to create negative mass. 
Even something as everyday like negative numbers only make sense if its missing items or debt. 

[kerbiloid]

When they had pour 10 t of petrol into a cistern, spent 3 t, and on the warehouse audit there is just 5 t inside.

Obviously, someone has added 2 t of negative mass and didn't say.

[K^2]

12 hours ago, magnemoe said:

Yes lots of stuff like this like tachyons, mathematical possible but unlikely to exist. 

With tachyons, at least we can show that if they do exist, under standard model, they don't interact with normal matter. So who cares? And usually, you can find these kinds of little gotchas that either make the result impossible or irrelevant. But there are also occasional edge cases where math says it's possible, but then we find zero evidence of it actually ever happening.

Another good example from GR is torsion. We assume in GR that space-time can only stretch and bend and we set torsion term to zero. Why? Because theory works with torsion set to zero. But there is absolutely no known physical reason why it should always be zero, and despite a lot of effort, we haven't found any indications that we're missing anything. There is a whole another degree of freedom in General Relativity and we just pretend it doesn't exist. It's worth also adding that this isn't just an artifact of Differential Geometry, which is what Einstein used to derive GR. If you derive General Relativity as Mean Field Poincare Gauge Theory  you end up with torsion as available degree of freedom. It's just apparently always zero - or the physics is somehow equivalent as if it was.  Aforementioned (aforelinked?) Einstein-Cardan theory tries to work it into the rest of physics, but the very fact that it makes no measurable difference is telling in its own right.

So yeah. There's math and there's physics, and while we use mathematics to describe the physics of the universe, sometimes we over-generalize and the real physics is just a subset of the mathematical model. And it often takes a very long time to figure out which parts are physical and which aren't.

[mikegarrison]

On 6/24/2021 at 8:23 AM, kerbiloid said:

When they had pour 10 t of petrol into a cistern, spent 3 t, and on the warehouse audit there is just 5 t inside.

Obviously, someone has added 2 t of negative mass and didn't say.

The warehouse workers don't drive cars fueled by petrol, do they?

[kerbiloid]

4 hours ago, mikegarrison said:

The warehouse workers don't drive cars fueled by petrol, do they?

They don't, but they needn't.

The negative mass was purchased by the truck drivers for the half of market price, lol.

Auditors and watchmen are trying to prevent the negative mass phenomenon.

Edited June 26, 2021 by kerbiloid