Can someone explain in simple terms what the Large Hadron Collider does (or is intended to do)?
Also, what impact does smashing protons (as it did) have on our understanding of the Universe?
Scientists are clearly very very excited, and I want in.
Thanks.
The primary goal of the LHC is to produce Higgs bosons, a theorized subatomic particle which is relevant for determining the masses of other particles. Other accelerators have tried and failed, but that’s not all that noteworthy yet, since it’s quite plausible that the mass of the Higgs is greater than the energies attainable by those accelerators. However, the LHC will be capable of energies higher than those, such that we should theoretically be definitely able to detect the Higgs: If its mass is too high for the LHC to produce, then there are serious problems in the theories that predict its existence in the first place.
As a side benefit, there are many other hypothetical particles that are also believed to be in this same energy range (or at least, for which it’s reasonable that they might be in this energy range), and if we detect any of those, it would also greatly advance our understanding of the way the world works. These might include susies (“partner” particles to the ones we’re familiar with, predicted by supersymmetry theories), monopoles (a particle with a magnetic north pole without a south, or vice-versa), or (if we’re really lucky) microscopic black holes (though those are mostly wishful thinking).
And, of course, most exciting of all, there’s also a pretty good chance that it’ll produce something completely new that we haven’t even anticipated. New scientific instruments historically tend to have that effect.
In even more basic terms:
You’ve heard of E = MC^2, right? Energy equals mass times the speed of light squared? On a very basic level mass and energy are interchangeable. That’s what makes the sun shine. Hydrogen atoms combine into helium atoms and lose a little bit of mass in the process. That lost mass is converted to the light and heat that reaches us here on Earth.
The LHC uses magnetic fields to accelerate protons to very, very high speeds. That means they have a lot of kinetic energy. And if you smash two very fast protons together, some of that kinetic energy will be converted to mass, just the same way that some of the mass of two fusing hydrogen atoms gets converted to sunlight.
The result is the temporary creation of new very heavy particles. These particles are unstable – they only stick around for a few tiny fractions of a second before they break apart again into lighter particles and energy. However, we can study the debris that’s left behind to reconstruct the properties of those temporary heavy particles.
Bigger collider = higher speeds = more kinetic energy = heavier new particles created during the collision.
By looking at how these heavy unstable particles behave, we can learn new things about how the universe works. For example, as **Chronos **points out, it’s hoped the LHC will shed some light on why familiar particles like electrons and protons have the masses they do (or even have masses at all).
So, on collision of the two protons, energy is being converted to mass?
What I’m reading on some sites say that the collision created 7 TeV. Isn’t that energy created by the collision? Or is it actually 2 protons, each accelerated at 3.5 TeV each, which when collide converts the energy from these protons to heavy particles (mass)?
Other questions:
These proton beams are traveling at almost the speed of light, correct? Doesn’t that affect the mass of the proton itself? If so, how is the experiment sustainable at speeds close to C? Is it because the mass of the proton is 1.672621637(83)×10−27 Kg and it doesn’t increase much in relative terms when it approaches C?
How does the temperature play into all of this? I understand that the temperature inside the hadron collider is close to absolute zero. Some sites are saying this is the coldest place in the Universe. Is that correct? How are they achieving this temperature?
Are the beams accelerated over time or is it instant? How long did the beam take to achieve 3.5 TeV and a speed of near C? If the collider is shut down, or a given experiment is concluded, does it mean a lead time is required before it achieves this speed again? Does that mean we will see only one experiment every x months?
Is it theoretically possible to encounter microscopic black holes or anti-matter in the LHC? And do we have theories which we can test, or is it just that under unknown circumstances these could appear?
Does the uncertainty principle affect the data we collect from these experiments?
Lots of questions. Take your time. Or answer only those questions you know about or care to address.
Thanks.
Forget anything you’ve ever learned about mass increasing close to the speed of light. That’s an outdated way of describing relativistic effects; it’s much simpler to say that the particle’s mass remains unchanged, but it just has a whole lot of energy.
The equipment needs to be kept pretty cold for the superconducting magnets to work, and it may be colder than any known naturally-occurring temperature, but laboratories have gotten temperatures far colder. They probably use liquid helium to maintain the temperature, which is produced using an extreme version of the process used in your refrigerator.
It takes months to build the beams up to full energy, and trying to shut down instantly would probably break something, but once the beams are up to full energy, you can do many, many collisions. There are a lot of particles in the beam, and only a very small fraction of them actually take part in any given collision.
Antimatter is an absolute certainty: Colliders with energies a thousand times lower than the LHC will produce antiprotons. There are some models that predict that microscopic black holes might be produced, but those models are extremely speculative, and I don’t think anyone actually expects they’re likely to be true. Microscopic black holes would be a sort of lottery jackpot for the LHC: The probability is low, but they still get a lot of attention because the payoff would be huge.
Absolutely, but we’ve had enough experience to learn what the proper questions are to ask, to which we can get solid answers. So in practice it’s not a problem.
Dude…you coulda stopped at 1.67.
As for lows temps, this is the dirty little secret of how its actually done.
They take all the male nerd physicists and put them at one end of the tube.
They put all the female nerd physicists and put them at the other end of the tube.
The male nerds then yell really lame sexist jokes into their end of the tube. The female nerds hear the jokes, and then they direct their icy cold stares of disapproval back down the tube. And then, before things warm back up, they quickly seal the thing back up and power that baby up.
They’re currently colliding two protons, each with 3.5 TeV, giving a total of 7 TeV. They intend to achieve twice that, 7 TeV per proton for 14 TeV. The actual collisions are between quarks, one from each proton, so they’ll really only have a third of the 7 or 14 TeV available for particle production.
The Wikipedia page says they can also collide lead nucleii with 574 TeV each.
The rest of your answers were pretty spot on, but this is not true. Going from no beam to 3.5 TeV beams takes a few hours in the worst case and can often take ~1 hour. Once you have beams, they typically last maybe 8 hours or so - reaching even a full day off a single fill would be pretty fantastic. The problem is not so much that protons are lost from the collisions, but that they are lost to interactions with gas in the beamlines or are kicked out of orbit or whatnot.
Also, dumping the beams quickly is an important safety feature of the LHC. How they do this is quite impressive, and you can read some about it here if you’d like: LHC beam dumps
What you might be confusing this with is that it takes a great deal of time (months) to cool and warm the LHC. Its difficult to cool the machine because it has a great deal of mass, and superfluid helium has a very small heat capacity.
yes.
Heh 
I used the ctrl-v beam to post that. The only number that I know beyond two decimal places is Pi.
What added advantage do we get from higher energies? At these levels (i.e. 3.5, 7, x, etc.), is the increase linear or exponential, in terms of the opportunities of breaking new ground. What is the value at which we can play God?
So as long as the temperature is maintained we can woohoo experiment like a motherfuck?
As was mentioned earlier, the reason you want higher energies is that you can study particles you wouldn’t be able to otherwise. For example, a particle with mass around 1 TeV is very difficult to study at the previous accelerator, the tevatron, but can be studied much more easily at the LHC.
The reason for this is that when you collide protons, you’re really colliding the quarks inside them. There’s a lot of complicated physics that goes into this, but the basic idea is that you never get the full energy, but rather some fraction based on how much energy the quarks inside you’re colliding have. For example, the Tevatron is 2 TeV, but you’ll never really produce a 1 TeV particle there.
There are a lot of reasons to believe there’s some interesting stuff going on at masses around 1 TeV and above, so we’d like to be able to produce particles with those masses. In particular, there are some things in our current theory that don’t make a whole lot of sense (predictions of probabilities greater than one and stuff like that) unless we do find as of yet experimentally undiscovered particles, which leads us to believe the whole thing is worth the effort.
Pretty much. The plan right now is to run through to the end of next year, then warm it all up, do a bunch of improvements, and start again after a year of working on the machine.
Sorry for the double post, but I reread this, and I think I understand what you’re saying better. You’re asking, why does it matter that we get 14 TeV instead of 7 TeV?
The answer has to do with how much energy the quarks have. Lets say you need 1 TeV of energy to produce your new magic particle. Unfortunately, even if you collide 3.5 TeV protons on 3.5 TeV protons, you typically don’t even get 1 TeV in the collision. In fact, its far more likely that you get only a small fraction of the energy out. Each little bit more you need makes it that much unlikely you’ll produce the particle.
To quantify this, we talk about things called cross sections. This is basically the probability to produce something at a given energy. If the cross section goes up by 2, you will get twice as many of those somethings if you collide protons at the same rate.
Because 1 TeV is a smaller fraction of 14 TeV than of 7, the cross sections for producing most things goes up dramatically from 7 to 14. For light particles, its typically a factor of ~4. For relatively heavy things, it can go up by a factor of 10 or more. This means that assuming we collide protons at the same rate, we will collect the data we’re interested in at a rate 4 to 10 times as high at 14 TeV than at 7 TeV. That means that we can discover new things basically 4 to 10 times faster. I think that’s a pretty good thing.
Quoth billfish678:
What, both of them?
And Krinthis, I stand corrected. I’m a theorist, not an experimentalist, and sometimes I get details of experiments like that wrong.
But why don’t they just ‘explode,’ so to speak? I always thought that kinetic energy had to be dissipated as heat. When a meteorite hits the Moon, doesn’t it blow up? 
Everything turns to heat, eventually. But in the meanwhile it might do some very interesting things first.
Probably a stupid question but I’ll ask it anyway.
What is the source of the protons in the proton streams that are being accelerated by the LHC? Are they generated, introduced, created?
Mail order from ACME. 
Uh-oh. I know what happens to the stuff you get from them in the roadrunner cartoons.