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Trying to Understand Gravity

September 29, 2008 on 2:26 pm | In Gravity, Q & A, String Theory | 41 Comments

Sure, gravity sounds like a pretty simple idea, now that we’re used to it. But, how does it work?

Think about it for a minute. What is gravity? It’s the idea that anything at all, with any mass or energy at all, in the whole Universe, is attracted to everything else with mass or energy in the Universe. This is true for familiar things that are near, but not touching Earth,

and it’s also true for things that are on (and touching) the surface of the Earth,

and it’s even true for objects that have nothing to do with the Earth at all:

But how does this work? Or in other words:

How can two things that don’t come into contact with one another exert a force on one another?

Newton didn’t know the answer to this, and he made up the phrase “action-at-a-distance” to explain it.

Nice try, wig-boy. I know that giving something a fancy name doesn’t actually explain what it is! (As an aside, that’s exactly what we’ve done now, over 300 years later, with dark energy.) So we go from wig-boy to wall-socket licker:

And this time, we actually get a deeply profound answer: all objects with mass and energy are connected through spacetime. So the Earth bends space around it, and that’s why things that are closer to the Earth are more attracted to it.

This same principle works with everything, including the gravity from the Sun, and even light from distant stars! If you look up at the sky near the Sun during a solar eclipse, you will find that stars are out of position, because the Sun’s gravity even bends starlight!

And so now, 400 years after we tried to answer the question of how gravity works, we realize that we still don’t have an answer for what happens at very small distances. This is what people working on quantum gravity are trying to discover, and honestly, this is the big hope of people who work on string theory: that strings will solve this problem.

Will it? It hasn’t so far, although no other solution looks promising. Any ideas as to how gravity really works? Hopefully, we’ll find one theory that explains it successfully for both strong and weak fields, and for small and large distances.

Weekend Diversion: Did I make the right call?

September 27, 2008 on 2:05 am | In Random Stuff | 7 Comments

When you’re a mathematically inclined Jew from New York, what are you encouraged to be when you grow up? Maybe, I don’t know, an investment banker makes the list?

And what, exactly, does that look like in today’s climate?

Who knew that choosing to be an astrophysicist actually would wind up being the more secure career choice?

A New Hint at the Expanding Universe?

September 26, 2008 on 2:05 am | In Dark Energy, cosmology | 51 Comments

Dark Energy. You’ve heard the name before. What it really is, though, is the name we give to the expanding Universe that we don’t understand.

Imagine that the big bang, the birth of the Universe as we know it, is like a giant explosion in space:

So things start off moving away from one another very rapidly. Now you can imagine three different cases. Perhaps the energy of the explosion is so great that the Universe will expand forever, that its gravity will never pull it back together. We call this an “open” Universe. Or perhaps there’s enough matter and energy in the Universe for gravity to pull everything back together into a single point at some distant time in the future. We call this a “closed” Universe. Or, maybe we live on that finely balanced line between those two extremes, and we’ll just asymptote to some expansion rate where it never recollapses, but the expansion eventually slows to zero. We call this a “flat” Universe.

Well, over the last decade, our measurements have finally gotten good enough that we can discriminate, and determine the type of Universe we live in. The verdict? It’s NONE of these! What we actually observe looks like the “flat” case for a little while, but the expansion rate stops decreasing all of a sudden, and does this:

Now, this is bizarre. But there’s news that the story gets even weirder. Apparently, when you look at hundreds of distant galaxy clusters, you find that they’re all moving, peculiarly, towards the same spot in the sky:

Now, to be fair, this was measured with the WMAP satellite, which wasn’t really designed to measure this effect, and we also don’t really understand what we’re seeing, and we don’t understand the velocity flows that we see in our own local group, much less in clusters billions of light years away. So there is a lot of room for error. Still, this is, at the very least, something that needs to be explained. Know where I’d look to for either confirmation or refutation? Europe’s Planck satellite. Launch date? February 2009.

We won’t have to wait long, just another couple of years… and I swear, that’s actually short for a science experiment! And then we should be able to measure this effect with some real precision and accuracy. And just maybe, we can figure out what the heck is up with this expanding mess that, to be honest, nobody really understands.

The Silver Lining of the LHC Accident

September 24, 2008 on 1:14 pm | In Physics | 8 Comments

Weren’t we all so excited about the LHC, which had completed successful tests and looked to be in tip-top shape? This giant ring accelerating protons in both clockwise and counterclockwise directions was going to collide them into one another with record-breaking energies (at least for Earth): 14 Tera-electron-Volts, or 7,000 times the energy that you get from a proton at rest.

All of this fancy equipment is underground in tunnels beneath the Franco-Swiss border. Including miles and miles of electromagnets, which you need in order to keep the beam moving in a circle. Think about it: protons are charged particles, and if you want to bend a charged particle, you use a magnet. As the protons go faster and faster, you need your magnet to be more and more powerful to keep it moving in a circle. So you use electromagnets. Want an even stronger magnetic field? Try cooling the electromagnets, and you can pump more current into them faster, creating a stronger field.

So that’s how they keep these super-fast particles moving in the circular underground ring. In order to make the fields as strong as they do, you need to cool these magnets a lot. Know how much a lot is? They cool it with liquid helium, which has a boiling point of only 4 Kelvin! You need to be very careful when you store liquid helium, obviously. Especially when you’ve got it running through hundreds upon hundreds of electromagnets underground. The liquid helium at the LHC is kept at 1.9 Kelvin, and is run through a series of tubes to cool the electromagnet that it surrounds:

These tubes are then welded together and enclosed within the underground tunnels:

The problem? There was a small fault that opened up in one of the cylinders. And what happens to liquid helium in a tube? Same as any liquid in a broken tube: it leaks.

About one ton of liquid helium leaked out, causing about 100 of the supercooled electromagnets to heat up and fail. How long until this is fixed? The best estimates say six to seven more months, which means April 2009 as an optimistic estimate. They won’t even be able to survey the damage for another three weeks; apparently when your entire tunnel is at 4 Kelvin, it takes awhile for it to heat up enough to allow humans inside.

So, this is a substantial setback for the LHC. But there is a benefit to physics in the US: it means that Fermilab, the current record holder in terms of high-energy experiments, gets an extra 6 months (at least) on top:

This also means that all the physicists working at Fermilab likely have another six months before their funding is pulled. I have a lot of friends from graduate school who are working there, and they’re certainly worried about what will happen to their careers once the LHC is fully operational. (And rightfully so!) The LHC looms large and ominously for Fermilab, kind of a metaphor for something I’ve seen before:

It’s possible that Fermilab will beat the LHC and discover the Higgs before the LHC is ready; this accident, although a huge setback for physics as a whole, buys Fermilab physicists more time in their endeavors to do so.

So what will their results be? Well, they just ruled out a Higgs mass of 170 GeV, and Higgs masses below 110 GeV has previously been ruled out. The most common prediction is for a Higgs mass of between 120 and 140 GeV, so hopefully we’ll hear some very interesting news soon!

Random Ranting: What happened to my country?

September 23, 2008 on 10:44 am | In Random Stuff | 16 Comments

Do you remember being a kid in elementary school, learning about why America was the best nation in the world? Learning what made our country so special and so great? You should remember, because there was a big federal campaign when I was a kid to teach everyone that:

The basic message is that America is great because of all the different freedoms we enjoy. Even this crazy guy agrees. No matter who you are, you’re allowed to be that person, and you have the freedom to both enjoy being that person and to enjoy not having your personal rights trod upon by any government agency.

At least, I thought that was something that America had, and that Americans valued. But let me tell you a little story, and I’ll try to illustrate it with some helpful pictures.

Our story begins last month, when I got a speeding ticket. First off, I will fully admit I was speeding, and I won’t pull a defense like this:

But I wasn’t speeding by as much as the ticket said, and so I planned to contest the ticket in court. I paid close attention to what the officer said:

  • Your court date is in bold on the ticket.
  • You must either pay the fine or show up in court at the time on the ticket.
  • If you cannot make that time you can call the courthouse to reschedule.

And that was it. I read through the ticket for any special instructions, and there weren’t any, so I figured I would just go to court on my appointed day. Which was today. So this morning, I have an 8:30 AM appointment at the Multnomah county courthouse:

And traffic was bad, but I planned ahead and left extra early. I walked through the courthouse door at about 8:25. Nowhere on the outside of this building are there regulations posted for what isn’t allowed inside. So they make me empty my pockets, take off my belt and shoes (really?! My shoes??), and go through the metal detector. And they pull me aside, and tell me that I’m not allowed to have this.

My Buck Knife. With a 1-1/4″ blade. The knife that I’ve carried around in my pocket every day since I’ve gotten off the Appalachian Trail. Nowhere in any documentation I’ve received is there any mention of no pocket knives allowed inside. Nowhere on the building is there any mention of what is or isn’t allowed inside.

Fine. So I tell the security guard that I’ll leave the knife with him, I won’t take it inside, and I’ll come back and get it when I leave. He tells me no; either I have to go back to my car and leave it there (in which case I’ll be late for my court date), or I have to let him throw it out.

What would YOU do in this situation?

  1. Cause a scene, yelling about your rights to your property, quoting the second amendment for good measure?
  2. Go back to your car, keep your knife, miss your court appointment, and hope they’ll excuse you for being late?
  3. Let the court security guards steal your knife and go to court on time; after all, your ticket was much more expensive than the knife?

I chose the third option. So after tearing through the halls to get to room 106 before 8:30 arrives (I was held up at security for a few minutes), I… discover there’s a giant line I have to stand in!

Apparently, this is the line for entering the plea that allows them to consult with the officer and set a court date in the first place, and although it isn’t written on the ticket and the officer didn’t tell me so, apparently I could have just done this by phone.

Live in Multnomah County? Have a ticket? Call the courthouse at 503-988-3235.

So I went through all of that and allowed the local government to steal my property to make a “court appearance” that doesn’t even count. Even though I went to the place on the ticket under the heading “Your Court Appearance Date/Time and Location”. They told me that they’ll select a court date at the officer’s convenience and notify me by mail in two weeks. They also told me if I don’t get anything in the mail, it’s my responsibility to call their office and find out when my appointment is. They expect it will be sometime around Halloween.

Needless to say, I’m really super pissed.

So that was my morning: having my property stolen by the Government while I ran through the red tape of filing forms with the courthouse so that I could get a new court date for a trial to contest my ticket. It kills me that this is just acceptable, that I’m supposed to shrug my shoulders and say this is how it goes. My country needs to be better than this. I can’t bring myself to settle for this version of America. What can I do in this situation? And what would you do?

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