Interesting...

**Imperator Romani** · June 30, 2009, 11:05 PM

As the title says, I think that this is really interesting.

http://news.yahoo.com/s/livescience/...soniclookslike

Didn't know you could get that on camera.

**Playfishpaste** · June 30, 2009, 11:08 PM

It's just like the stuff that comes off of planes in contrails, just as a higher pressure.

A beautiful site indeed.

Now what would be really cool is seeing a plane get some cerenkov light off of it. http://en.wikipedia.org/wiki/Cherenkov_radiation

**Baron von Sky Hat** · July 01, 2009, 06:28 AM

It's a very cool effect, yeah. Spectacular image, really makes it seem like the sound barrier is a literal physical thing that the plane is smashing through despite that not being the case.

Originally Posted by Playfishpaste

It's just like the stuff that comes off of planes in contrails, just as a higher pressure.

A beautiful site indeed.

Now what would be really cool is seeing a plane get some cerenkov light off of it. http://en.wikipedia.org/wiki/Cherenkov_radiation

It doesn't seem to be the same as contrails, in fact. Contrails are from engines of planes, where the particles left behind from the exhaust provide nucleation points for water to start forming droplets, basically the same as how clouds work.
However these vapour envelopes from breaking the sound barrier, I'm under the impression, are different. Not down to particles specifically providing nucleation points, but seem to be some effect on the air itself providing conditions necessary to trap water vapour temporarily. I think that it is the same effect that can sometimes be seen above the wings of aircraft during high-g turns. This is the first example I could find from a quick google search:
http://farm2.static.flickr.com/1389/...abc34e.jpg?v=0

I'm not sure what you think could be done to create Cherenkov radiation, however? It requires high energy, fast charged particles which would be moving faster than the local speed of light. You get it in the water around nuclear reactors, the reactor causes high speed electrons in the water which results in Cherenkov light, a kind of bluish glow iirc. The effect is also used extensively in particle detectors in physics experiments. So I'm not sure what you are referring to with regards to aircraft?
I do agree that the appearance of the Cherenkov effect is extremely cool though

**Playfishpaste** · July 01, 2009, 05:17 PM

What I meant was that both were high concentrations of watervapor being shoved under pressure. One however is at extremely high pressure, and the fluid dynamics behave shockingly differently.

As to the second one, it would be a real feat for a plane to produce Cerenkov radiation in flight, because that would mean it was going faster then the speed of light through air. That would be something pretty amazing and shocking. Breaking the sound barrier not so much.

Course, you could always take the plane through some bose einstein condensate at 1 mph. Cheating is for sneaky scientists though, engineers are too proud :]

**Baron von Sky Hat** · July 02, 2009, 08:19 AM

I'm not sure that that is the case though, in fact. The contrails are not a result of any pressure induced by the aircraft, merely that the aircraft provides particles which water molecules can `accrete' to to form droplets. The supersonic `cone' of vapour and (I think) the wing vapour in high-g turns does seem to be a result of direct pressure profiles in the air surrounding the plane due to the fluid dynamics of the flow around the plane.

As to the plane moving faster than local speed of light. It's an interesting concept, but I think implausible. I don't think I can see any concept that would permit a solid object to stay as a solid under those circumstances. It would equate to an extremely high energy collision, collisional heating would be extraordinarily high. A single oxygen atom in the air would hit it with an apparent kinetic energy of something like 1E-9 Joules. While that may not seem big in number terms, when you consider that that is at an atomic scale its huge. For comparison, I think that's at least an order of magnitude more than the energy release by one uranium-235 atom undergoing fission... Obviously not all of that would necessarily be transferred directly to heating, but it gives a good idea of the scale of energy for collisions at these velocities.
More importantly, everything I know about the Cherenkov effect refers pretty much exclusively to single particle trajectories, usually high energy electrons. I'm pretty certain that this is because it doesn't deal with the effects of physical collisions with component atoms of the fluid/material being traversed. Any such collision would reduce the speed of the particle by a huge amount, likely below the local light speed. It is due to the interactions of the fields of the system (hence the particle needing to be a charged one) that Cherenkov light is emitted.

I'm not anything of an authority on Bose-Einstein condensates, but I'm fairly sure from what I know that they are extremely fragile with regards to temperature. I think that even collisions with normal velocity, room-temperature particles can break down the condensate, since it can easily begin to raise it past its very low condensation temperature (I think something in the vicinity of well less than a micro kelvin). That said, assuming you could create enough of a Bose-Einstein condensate that for some reason wouldn't break down, I have no idea what would happen as something traveled through it... :S
What properties do you think they have to result in Cherenkov radiation? I'm not familiar with the ins and outs of Bose-Einstein condensates, so I can't think what it might result in. I was under the impression that at such low temperatures the interaction between the atoms becomes low enough that they all start falling to their ground states, providing a material with very non-standard properties?
I don't think effects of macroscopic solid objects in Bose-Einstein condensates have been considered (at least, not much, if they have at all) because of the huge difficulties that would surround such a situation occurring. Not certain though, I may have a look for some papers on Bose-Einstein Condensates to see what's being done in the fields relating to them.

**Playfishpaste** · July 02, 2009, 02:38 PM

Originally Posted by Baron von Sky Hat

I'm not sure that that is the case though, in fact. The contrails are not a result of any pressure induced by the aircraft, merely that the aircraft provides particles which water molecules can `accrete' to to form droplets. The supersonic `cone' of vapour and (I think) the wing vapour in high-g turns does seem to be a result of direct pressure profiles in the air surrounding the plane due to the fluid dynamics of the flow around the plane.

As to the plane moving faster than local speed of light. It's an interesting concept, but I think implausible. I don't think I can see any concept that would permit a solid object to stay as a solid under those circumstances. It would equate to an extremely high energy collision, collisional heating would be extraordinarily high. A single oxygen atom in the air would hit it with an apparent kinetic energy of something like 1E-9 Joules. While that may not seem big in number terms, when you consider that that is at an atomic scale its huge. For comparison, I think that's at least an order of magnitude more than the energy release by one uranium-235 atom undergoing fission... Obviously not all of that would necessarily be transferred directly to heating, but it gives a good idea of the scale of energy for collisions at these velocities.
More importantly, everything I know about the Cherenkov effect refers pretty much exclusively to single particle trajectories, usually high energy electrons. I'm pretty certain that this is because it doesn't deal with the effects of physical collisions with component atoms of the fluid/material being traversed. Any such collision would reduce the speed of the particle by a huge amount, likely below the local light speed. It is due to the interactions of the fields of the system (hence the particle needing to be a charged one) that Cherenkov light is emitted.

I'm not anything of an authority on Bose-Einstein condensates, but I'm fairly sure from what I know that they are extremely fragile with regards to temperature. I think that even collisions with normal velocity, room-temperature particles can break down the condensate, since it can easily begin to raise it past its very low condensation temperature (I think something in the vicinity of well less than a micro kelvin). That said, assuming you could create enough of a Bose-Einstein condensate that for some reason wouldn't break down, I have no idea what would happen as something traveled through it... :S
What properties do you think they have to result in Cherenkov radiation? I'm not familiar with the ins and outs of Bose-Einstein condensates, so I can't think what it might result in. I was under the impression that at such low temperatures the interaction between the atoms becomes low enough that they all start falling to their ground states, providing a material with very non-standard properties?
I don't think effects of macroscopic solid objects in Bose-Einstein condensates have been considered (at least, not much, if they have at all) because of the huge difficulties that would surround such a situation occurring. Not certain though, I may have a look for some papers on Bose-Einstein Condensates to see what's being done in the fields relating to them.

The condensation of the vapor, and the ensuing saturation of the air, is caused by pressure differentials.

At the same time, ya don't need to make it all brute thrust. How bout if we have the plane go through a wormhole or make it out of entangled tachyons?

Bose Einstein Condensates can slow the travel of some subatomic particles as well as light significantly, to the point where you could actually walk faster then the speed of light. If you were inside of the condensate whilst doing this, you'd give off cerenkov radiation, though there would be complications given the weird nature of the material.