Cern throws switch on largest machine ever built

16:05 BSTThe guys at Cern have repeated this morning's success by sending a second beam of protons around the LHC in the opposite, anticlockwise direction. And like this morning, they completed the task in around an hour. The relief and delight on their faces is brilliant.

I've just spoken to Chris Llewellyn-Smith, who was director general here at Cern when the LHC was given the go-ahead in the mid-1980s. He was tired but elated. "It's fantastic. I've waiting so long for this," he said.

Now the real work begins. The beams are not yet circulating precisely enough. The physicists will need to tweak the magnets that surround the LHC's ring to make the beams, which are only a hair's width across, travel down the very centre of the pipe that contains them. If they can't do that, they won't be able to collide two beams head on.

That could take a few days. For the moment, though, the place is full of tired, happy looking scientists. It's been a great day for them.

If you want to read about the safety of the Large Hadron Collider, there's some good information here.

See our online guide to the Large Hadron Collider, with articles by Stephen Hawking, Sir Martin Rees, AC Grayling and the comedian Chris Morris.

13:48 BSTScientists have now started to send a second beam around the LHC, this time anticlockwise – in the opposite direction to the first beam. The beam is half way around right now.

13:03 BSTWe've just heard that there was a minor glitch with the cryogenics system of the machine this morning.

Cooling is absolutely crucial to the LHC's operation, with the superconducting magnets running at around –271C. It is these magnets that steer the beam around what at light speed is the incredibly tight curve of the LHC's ring.

Engineers say the glitch was nothing major, and they hope to try and send the second beam around very soon.

10:31 BSTThe morning has gone so well, the Cern team are going to attempt to send a beam around the machine in the opposite direction. That will be coming up in the next hour or so.

Verena Kain, a physicist on the LHC, had a few words to say about this morning's success: "I didn't believe it, I had to see it a second time. It's just going fantastically well. Everybody is just floating right now. It's a first step, but it's fantastic it works so well.

"If you're a person who's interested in the fundamental 'why', then at some point you have to ask the questions we're asking with the LHC. We've got to know these things."

09:33 BSTThat's it, they've made it. One lap down. Scientists have just pulled the last block from the 17-mile-long tunnel and seen the beam of protons appear at the last stage of the Large Hadron Collider. So protons have now circulated once around the machine. It has gone extremely well for the scientists here.

They've done it in under an hour. A great first day for a machine that will take us into a new era of physics over the coming decades.

That's the slowest beam you'll see going around the LHC, at around 20mph. When it's up to speed, a proton will make more than 11,000 laps in a second.

09:23 BSTThe beam has now reached the last detector, the enormous one called ATLAS. They are one sector away from a complete circuit.

09:04 BSTIt's a big day here at Cern, the European particle physics laboratory, on the outskirts of Geneva. They have begun switching on their Large Hadron Collider, the most powerful particle smasher in the world.

The man at the controls is Lyn Evans. He's a charismatic guy, running the show in jeans, white trainers and a stripey short-sleeved shirt. Yesterday, when I met up with him, he was in shorts and a tee-shirt covered in equations.

The beam is now more than half way around the Large Hadron Collider. Lyn said this morning that it might take two hours to get the beam around if everything went well. So far, all is going fantastically smoothly though.

"We are making very good progress. The beam is now half way round the LHC," said Evans. "At this rate, let's hope that within an hour, we'll get the beam the whole way round the LHC."

There are four giant detectors around the ring, where ultimately two opposing beams will be crashed into one another. So far, the beam has gone past two of these detectors. One of the detectors has already picked up emissions from the beam striking a block that was put in place to halt the beam.

08:46 BSTScientists at Cern, the European particle physics laboratory in Geneva, have begun their first attempt to send a beam of protons around the Large Hadron Collider, the largest, most complex machine in the world.

The beam of protons has been injected at close to the speed of light, but there are blocks inside the machine that stop it periodically as it works its way around. Each time the beam stops, the engineers can use magnetic fields to make sure the beam is travelling down the centre of the ring. If it's off to one side, it could crash into the ring wall and stop.

We've just seen the first flash of the beam in the machine. And it looks to be well in the centre of the pipe it circulates in. The beam has now made it around the first sector, which is an eighth of the ring

Lots of applause from Cern's control room. The last time they opened a particle collider, in the 1980s, it took 12 hours to get a beam to circulate. This is moving fast so far.

07:19 BSTThe big day has finally arrived. After 20 years of planning and almost a decade of building, Cern, the European particle physics laboratory, is ready to put its shiny new particle collider through its paces.

In an hour or two, Cern researchers will attempt to send a beam of protons around the Large Hadron Collider for the first time. If it works, it will pave the way for the first collisions in around a month's time. From then on, scientists will have 20 years or so to direct the machine's muscle at some of the most profound mysteries in science.

Cern is buzzing with activity this morning. In the press room I can overhear more languages than I can count. The good thing about being here at Cern, where Tim Berners-Lee invented the internet, is that you can be fairly sure the video feeds from the control room and the wireless networking won't crash halfway through the day. At least I hope that's a safe bet.

I was half expecting some protesters outside the gates this morning. Perhaps the odd placard pleading scientists to think again before throwing the big switch. But it seems that for all the bluster in the press, no-one is worried enough about the machine destroying the world to wave a banner or chain themselves to the gates.

The press, incidentally, are confined to a building called The Globe, which seems to be made of MDF.

Here's the way things are set to run today. We're expecting to kick-off around 8am UK time with live broadcasting from Cern's control room. That should give us some details of how they will send the proton beam around the machine. In the history of particle colliders, I'm not sure anyone has got a beam of particles to circulate on their first attempt.

We're due a briefing around 9am UK time, which will be very brief indeed, perhaps only enough time to say whether the first try has or hasn't worked.

Attempts will continue through the day. My money is on them attempting to send the beam anticlockwise first, though it makes no difference. If they get the beam to go one way, they'll try and send it round the other way too. If that works too, the machine will go through some fine tuning to make sure the beam runs down the centre of the ring, with collisions set for a month's time.

There's a bit of a racket that's just started up. Sounds like someone's tearing the very fabric of the universe. More posts to come as events unfold.