Large Hadron Collider Results by Christmas

[sheeny]

Found this snippet on nature this morning:



The story by Eric Hand requires a subscription.

Al.

[renormalised]

Here's another story on the LHC's start up....

http://news.zdnet.co.uk/emergingtech/0,1000000183,39710077,00.htm

and here's its homepage... http://lhc.web.cern.ch/lhc/ (http://lhc.web.cern.ch/lhc/)

[Morepower]

This has probably already been answered, but, if the beams are travelling toward each other at almost the speed of light at what relative speed do they collide at ? Nearly double the speed of light ? Or is there some "speed of light" rule preventing such collision velocities ?

[sheeny]

The thing about relativity is that what you see is relative to your reference frame.

So as more and more energy is poured into the particles, they approach the speed of light, c, but can never get there. The energy increases the relativitistic mass rather than adding velocity.

So we, standing at the LHC, see 2 particles crash together at a large portion of c each, however, from the point of view of one of the particles, the approaching or passing particle would appear to be approaching at a speed even closer to c and with more mass than we observe.

Al.

[sjastro]

If the 2 beams approach each other at say 0.99c, Galilean relativity or addition velocity doesn't apply as the approach velocity is 0.99c+0.99c=1.98c which obviously exceeds the speed of light.

Using special relativity the approach velocity is (0.99c+0.99c)/(1+(0.99c*0.99c)/c^2)= 0.9999c.

The reason this occurs is that in the LHC frame of reference, the time it takes for 2 opposing particle beams to collide with each other will take longer when compared to the particles frame of reference. This is time dilation which preserves the constancy of the speed of light in all frames of references and prevents observers measuring speeds greater than the speed of light.

Regards

Steven

[renormalised]

However, after Spock arrives at the LHC and says..."Fascinating, however, if you apply Dr Cochrane's....." and after 2 hours of dissertation on warp physics finishes with..."and then do this to the magnetic flux capacitors." ...both particles fly off at warp 9.5 to whatever part of the universe the LHC is pointing towards at the time, never to be seen again:eyepop::P:P:D:D

[Morepower]

LOL, try smashing some Dilithium Crystals together at 0.9999C. But maybe stand well back.

Thanks for the detailed explanation guys, I pretty much get it (and thought it was too easy) but it WASN'T what I wanted to hear. I hate the whole "speed of light" speed limit deal. I know the "Space-Time" thing allows for it but I see that as cheating.

I can't wait 'till they crank the LHC up to full power and start letting the particles fly. I am particularily interested in what they may learn about Gravity.

I have another possibly stupid question if you guys don't mind. And that is if you could actually be in one of the detectors when a collision occured, assuming it was completely dark, is there enough energy released that would allow you to see anything ? Like maybe a very tiny sparkle or something similar. I don't mean from high speed particles hitting the optic nerve/retina, or whatever happens to the astronauts when they see flashes, I mean light.

[sjastro]

It's not cheating it's based on observation. People have been measuring the speed of light since the 17th century and is found to be the same irrespective if the source is approaching or receding us.
Special relativity provides the explanation.

An interesting question. I wouldn't personally like to find out given that Gamma and X-rays are a byproduct of the collisions but the particles produced in the collisions will have energies of similar magnitude to cosmic radiation.

I find when I am taking dark frames for my CCD in my humble refrigerator, I have noticed my CCD (and frig) are under constant bombardment. The dark frames are littered with cosmic ray hits.

Since I don't directly perceive these hits myself I suppose the same principle may apply at a detector.

Steven

[renormalised]

You'd probably see flashes in your eyes, like the astronauts did on long duration flights, especially to the Moon. That was caused by cosmic rays, namely alpha particles, knocking electrons out of their orbits in the fluid inside their eyes. It's what they call Cherenkov Radiation. The electrons get knocked free then recombine with their atoms, and give off a blueish light. Same thing happens when a powerful magnetic field snaps, as it also would if something similar happened to a gravitational field. In going back to its ground state, the field causes molecules in the air (or in gravity's case, generates virtual particle pairs in the surrounding spacetime) to lose electrons which then recombine with the atoms/molecules and lose energy by giving off photons in the blue/UV part of the spectrum.