Exploring Hidden Dimensions at the World Science Festival

Since I was going to be down here anyway to sign books at the World Science Festival Street Fair, Kate and I decided to catch one of the Saturday events at the Festival. It was hard to choose, but we opted for the program on Hidden Dimensions: Exploring Hyperspace (Live coverage was here, but the video is off), because it was a physics-based topic, and because I wrote a guest-blog post on the topic for them.

(No, we didn’t go to the controversial “Science and Faith” panel, opting instead to have a very nice Caribbean dinner at Negril Village, just around the corner. I’ll take excellent Caribbean food over science-and-faith discussions any day…)

The panel consisted of three theoretical physicists (Lawrence Krauss, Brian Greene, and Shamit Kachru) and an art historian, Linda Dalrymple Henderson, plus a string quartet. I was a little uneasy about this going in, because it seemed like the science-and-art connection could get a little gimmicky. I was pleasantly surprised at how well it came together, though. It was a really good program, and a fun evening.

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Bohemian Mechanical Rhapsody

Blame Bryan O’Sullivan for this– after his comment about misreading “Bohmian Mechanics” as “Bohemian Mechanics,” I couldn’t get this silly idea out of my head. And this is the result.

I like to think that this was Brian May‘s first draft (he does have a Ph.D. in astrophysics, after all), before Freddie Mercury got hold of it:

Is this the real life?
Is this just fantasy?
Do objects have real states
Or just probabilities?

Open your eyes
Look up to the skies and see

Studying quantum (poor boy), I need no sympathy
Because I’m easy come, easy go
A little psi, little rho
No interpretation ever really matters to me, to me

Mama, just killed a cat
‘Least I think I might’ve did
Won’t know ’til I lift the lid
Local realism was fun
But now I’ve gone and thrown it all away
Mama, ooo
Didn’t mean to make you cry
If I’m incoherent this time tomorrow
Calculate, calculate, as if nothing really matters

Too late, my state’s collapsed
Sends shivers down my spine
Decohering all the time
Goodbye determinism- you’ve got to go
Gotta leave you all behind for random chance
Einstein, ooo – (anyway the wind blows)
God should not play dice
I sometimes wish I’d never read Born at all

I see a little silhouetto of a psi
Scaramouche, scaramouche will you do the fandango
Action at a distance, very very spooky to me

Gallileo, Gallileo,
Gallileo, Gallileo,
Gallileo where’d you go? I don’t know (oh, oh, oh)

I’m just a physicist, nobody loves me
No information has speeds more than c
Spare all our brains from non-locality

Easy come easy go – will you let me go
Bell’s theorem! No – we will not let you go

let him go
Bell’s theorem! We will not let you go

let him clone
No cloning! We will not let you clone

let me go
Will not let you go

let me go (never)
Never let you go
let me go
Never let me go – ooo
No, no, no, no, no, no, no
Oh mama mia, mama mia, mama mia let me go
Heisenberg has a matrix put aside for me
for me
for meeeeeee

So you think you can stone me and spit in my eye
And then decohere me and collapse my psi
Oh baby – can’t do this to me baby
Just gotta get out – just gotta get right outta here

Ooh yeah, ooh yeah
Nothing really exists
When no-one can see
Nothing really exists – nothing really matters to me

Anyway the wind blows…

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Quick Impressions of Bohmian Mechanics

I get asked my opinion of Bohmian mechanics a fair bit, despite the fact that I know very little about it. This came up again recently, so I got some suggested reading from Matt Leifer, on the grounds that I ought to learn something about it if I’m going to keep being asked about it. One of his links led to the Bohmian Mechanics collaboration, where they helpfully provide a page of pre-prints that you can download. Among these was a link to the Bohmian Mechanics entry in the Stanford Encyclopedia of Philosophy, which seemed like a good place to start as it would be a) free, and b) aimed at a non-physics audience, which is a plus, given the cold I have at the moment, which isn’t doing much for my clarity of thought.

It turns out I had read some of this before, and my immediate reaction now was the same as my reaction then, namely “It’s a miracle you can type while balancing that chip on your shoulder.” The introduction is fairly neutral, but as you go down through the article, there are a bunch of little shots at “orthodox quantum theory” which have the cumulative effect of making me start to wonder if the author is actually a crank– in the previous read (while I was writing How to Teach Physics to Your Dog), I actually gave up after a quick skim for just this reason. As the author is one of the authorities Matt recommended, I read it more carefully this time out, and what follows are some quick impressions based on reading through the article. I would not begin to claim that I have gained any deep understanding, and I’ll look at some more physics-oriented resources next (maybe the textbook Matt mentioned, though the freely available front matter had the same shoulder-chip issue noted above), but this is, as the title suggests, the stuff I thought of immediately.

The short version, above the fold to serve as both teaser and attention conservation notice is two items: 1) In many ways, this sounds like an unholy union between Einstein and Heisenberg, and 2) I still don’t see the point.

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Laser Smackdown: Final Days of Voting for the Most Amazing Laser Application

We’re just over 600 votes in the Laser Smackdown poll in honor of the 50th anniversary of the laser, as of early Friday morning. I notice that it has moved off the front page of the blog, though, so here’s another signal-boosting repost, just so we have as many votes as possible, to establish maximum scientific validity when we declare the winner the Most Amazing Laser Application of All Time

Voting will remain open until next Sunday, May 2, just two days from now, with the ultimate winner announced on Monday, May 3rd. So get reading, and get voting. One vote per computer per user, please– this is Serious Science.

Amazing Laser Application 11: Frequency Combs!

What’s the application? An optical frequency comb is a short-duration pulsed laser whose output can be viewed as a regularly spaced series of different frequencies. If the pulses are short enough, this can span the entire visible spectrum, giving a “comb” of colored lines on a traditional spectrometer. This can be used for a wide variety of applications, from precision time standards to molecular spectroscopy to astronomy.

What problem(s) is it the solution to? 1) “How do I compare this optical frequency standard to a microwave frequency standard?” 2) “How do I calibrate my spectrometer well enough to detect small planets around other stars?” 3) “How can I do precision molecular spectroscopy really quickly?” 4) “How can I do qubit rotations faster in my ion trap quantum computer?” among others.

How does it work? The key idea is that in order to make short pulses of light, mathematically, you need to add together large numbers of waves at different frequencies. I talk about this a little in the book, from which I’ll lift this figure:


From bottom to top, this shows a single frequency, the sum of two different frequencies, then three different frequencies, then five. As you can see, adding mroe frequencies gets you a shorter pulse (where the waves are obvious) with a larger gap between pulses.

When you do this with the right sort of laser, you can generate a pulse whose length is given in femtoseconds (10-15s, or 0.000000000000001s). That kind of ridiculously short length requires an extremely broad range of frequencies to make it up, which can be pictured as a “comb” of lines of different frequencies, corresponding to the different colored lines seen in this figure lifted from the group of Theodor Hänsch, who shared the 2005 Nobel Prize for developing the technique:


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So You’d Like to Learn Some Physics…

Via Twitter, Michael Barton is looking for some good books about physics. I was Twitter-less for a few days around the period of his request, and this is a more-than-140-characters topic if ever there was one, so I’m turning it into a blog post.

The reason for the request is that he’s going to be working as an intern at the Einstein exhibit when it visits Portland, which makes this a little tricky, as relativity is not an area I’ve read a lot of popular books in (yet– that’s changing). That will make this a little more sparse than it might be in some other fields.

There’s also an essential disclaimer here regarding the “teaching physics”/ “teaching about physics” distinction. If you want to learn physics at the level needed to do physics– solving problems, reading journal articles, etc.– there is no substitute for a good textbook. Read it, and do as many of the problems as you can, and try the ones you can’t. If you want an intro-level survey of the field, pretty much all introductory texts are equivalent– go to your local college bookstore, pick up whatever they’re assigning for Physics 101, and start working through it.

(If you want something specifically about relativity, try Six Ideas That shaped Physics Unit R. It’s got some idiosyncracies, but it’s a good explanation, and very readable as these things go.)

Assuming you want to learn about physics, rather than plowing through all the math needed to do physics, though, there are a number of good books out there.

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What Every Dog Should Know About Quantum Physics

I gave a talk today for a group of local home-school students and parents, on the essential elements of quantum physics. The idea was to give them a sense of what sets quantum mechanics apart from other theories of physics, and why it’s a weird and wonderful thing.

The title is, of course, a reference to How to Teach Physics to Your Dog, and the second slide was an embedded version of the Chapter 3 reading. I set the talk up to build toward the double-slit experiment with electrons, using the video of the experiment made by Hitachi. Here’s the talk on SlideShare:

It went really well, I think. There were thirty-ish students and parents there, and a number of the kids were really fired up about it. After the talk, I brought Emmy in to meet them, and then gave them a tour of a couple of labs and the college observatory, which was also a big hit. Several of them also brought books to be signed, and were really enthusiastic about the book, which is a kick.

I’ve exchanged some emails with a local high school teacher, and will probably try to set something similar up with them for later in the year. We’ll see. For now, this was a lot of fun, and I hope it was helpful to the students and parents in attendance.

Update: A post at the Home Physics blog, with a couple of pictures showing the talk in progress, and part of the tour.

Entanglement Happens

There have been a bunch of stories recently talking about quantum effects at room temperature– one, about coherent transport in photosynthesis , even escaped the science blogosphere. They’ve mostly said similar things, but Thursday’s ArxivBlog entry had a particular description of a paper about entanglement effects that is worth unpacking:

Entanglement is a strange and fragile thing. Sneeze and it vanishes. The problem is that entanglement is destroyed by any interaction with the environment and these interactions are hard to prevent. So physicists have only ever been able to study and exploit entanglement in systems that do not interact easily with the environment, such as photons, or at temperatures close to absolute zero where the environment becomes more benign.

In fact, physicists believe that there is a fundamental limit to the thermal energies at which entanglement can be usefully exploited. And this limit is tiny, comparable to very lowest temperatures.

(That’s cut-and-pasted– there are obviously words missing from the last sentence, but I don’t know what they are.)

Is this saying that entanglement does not happen at higher temperatures? No, it’s not. What’s going on here is a little subtle, so it’s worth talking a bit about (even though I know this will invite comments from crazy people).

The generic sort of entanglement experiment looks like this:


In the center, you have a black box that emits photons whose polarizations are entangled. That is, the two photons are guaranteed to have the same polarization, when they’re measured, but that polarization is equally likely to be either horizontal or vertical. Those photons travel out from the box to two detectors consisting of a polarizing beamsplitter that sends horizontally polarized photons to one detector (where a photon is registered as a 1), and vertically polarized photons to another (registered as a 0).

If the photons are entangled, when you look back over the results of many repetitions of the experiment, you will always find pairs of identical numbers. If one detector gets a 0, the other also gets a 0 (I’ll call this “00” to keep things compact); if the one gets a 1, the other also gets a 1 (“11”). When you look over a long list of results of the experiment, you’ll see roughly equal numbers of “00” and “11” results, but never a “10” or a “01” (assuming ideal detectors, etc.).

Of course, this has left out the possibility of interaction with the wider world, so let’s think about what happens if we do something to one of those photons en route to the detector. Imagine that a tiny demon, bored with sorting hot and cold molecules comes along and sticks a polarization rotator in the path of one of the two photons, like this:


What happens then?

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