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J. O.:
Thanks for the post! It immediatley put me in mind of Feynmans' book "QED..." which never fails to raise the hair on the back of my neck when I read it. (Usually a couple of times a year, just because it's so much fun!) I enjoy the blog daily, (as you make new entries), please keep up the great work.

Great post, thanks for writing it! I don't really find anything geeky about learning about the universe, though. It's fascinating.

I enjoy your blog, and particularly this post, but I'm compelled to ask: how can two things be "about a fraction of an inch apart?" Can they be exactly a fraction of an inch apart? :)

re: why faster electrons become "classical" particles...

-The faster the electron (i.e., the more momentum it has) the shorter its (de Broglie) wavelength.
-The shorter its wavelength, the smaller the scale of the interference pattern.
-The smaller the scale of its interference pattern, the more particle-like (i.e., "classically") it behaves.

This explains why they had to speed up the slow electrons rather than just use the fast ones: the fast ones had so much kinetic energy that they were already acting classically.

The separation of the two nuclei in a hydrogen molecule will be on the order of 1 Angstrom; as the wavelength of the electron gets down to this value (by speeding up), the interference pattern is stretched to the point that the minima disappear. Which is to say, the electron appears to travel straight through the "slit" without diffraction, as a particle would. For reference, an electron has a wavelength of 15 A when traveling 1% of the speed of light (which may sound fast, but consider that the electron beam in an old-fashioned CRT television has about half of that speed.)

(N.B. I am not a quantum physicist, but as I have a doctorate in astronomy I sometimes pretend.)

Stupid question? I thought hydrogen, by definition, only had one proton.

That's not a stupid question at all, Lauren. We're actually talking about a simple hydrogen MOLECULE in this instance, not an atom. A hydrogen ATOM, by definition, has only one proton and one electron (although the isotopes can have varying numbers of neutrons).

And thanks to Bemopolis for summing up the answer to my own query so succinctly and clearly.

M.L.: QED is my fave Feynman book, too...

Now QM is pretty bizarrely different from the expectations we import from the world of medium sized objects but if we didn't insist on explaining it in such an inappropriate and paradoxical fashion it would be a lot less mind boggling. Some of the problems with the standard explanation (you just did a good job presenting it so I don't mean to criticize you) are the following.

1) Electrons/Photons/etc.. are neither particles nor waves not both. (and the wave/particle duality is just a philosophically boring statement of approximate behavior).

Electrons/photons are not both waves and particles they are wave functions. Wave functions are just their own thing that behaves as QM says they do. The fact that these wave function objects tend to have different limiting behavior in different conditions doesn't show any deep duality in their nature.

2) Photons/Electons/etc.. are not in two places at once and it's misleading to talk about them going through both slits at once.

When a water wave goes around both sides of a rock or enters a harbor through two slits we don't describe this as the water wave being in two places at once. We understand that really the water wave is an extended object that can (non-paradoxically) occupy an entire region of space at one time. Saying that the water wave goes through the left entrance and that the water wave goes through the right entrance too is technically valid but misleading since it suggests that the wave goes entierly through each entrance.

Now it's an interesting fact about wave functions that they act very very differently (well if you accept a many minds interp our observations of them are very different) if you place a detector on the slits but so what? This doesn't justify suggesting this is in anyway analogous to a normal medium sized object spookily being in two places (which I didn't notice you doing but is common).

3) The position/momentum of elementary particles are not uncertain. These properties just don't apply to wavefunctions.

Asking for the position of a photon except when it is localized by collapsing into a position basis is just as wrong as asking what's the 'real' position of a water wave. A wavefunction is usually an extended object that doesn't have a precise position similarly with momentum. In fact the EPR paradox shows that these properties simply don't apply except in the rare case when the wavefunction is totally collapsed into that basis.

Anyway sorry for the rant. I liked your post but I just have a pet peeve about the whole standard analogy for QM.

As any electrical engineer would assure you, it's all about Fourier transforms. Taking the piss out of Paris Hilton is another matter entirely. She is a goddess and I worship her - my distinction in Part III of the Cambridge Mathematical Tripos notwithstanding.

Everyone has their pet peeves about common explanations of QM, including my own Spousal Unit. Feelings can run very high on the issue. And every peever is convinced that his/her approach is so vastly superior that any non-scientist encountering it will be immediately enlightened into a depth of understanding hitherto unachieved. They are usually mistaken. :) The reason the popular explanation is so popular is because the average non-scientist is not going to grasp the abstract concept of a wave function. So we give them a simpler, more concrete way of visualizing it; this gives them a rudimentary grasp of what's going on, preparing them for the next stage. Eventually, they WILL be able to grasp the finer nuances you outlined above (although I can think of lots of folks who'd nitpick with some of YOUR statements). But for a blog called Cocktail Party Physics, we'll stick with our take, thanks very much.

That said, I did have a section in an earlier draft of the post drawing out the anaology of water waves as you described, so I'm glad you brought it up. I cut it because the post was getting too damn long and I'm trying to write just a tad more succinctly. But one of the reasons for writing the blog in the first place is to fine-tune things like my approach to explaining wave/particle duality, and I think I can work a couple of your points into the next version without sacrificing that lay-level clarity and simplicity I'm always shooting for. So thanks!

As for poor Jongleur, this week's episode of HOUSE dramatized his predicament very nicely: The mighty, sarcastic House hires a beautiful woman as a team member because her looks blind him to the fact that she's just not as sharp about the medicine as the rest of his team. She makes inane diagnostic suggestions and he thinks they make sense because, hey, she happened to be wearing a see-through blouse that day. (Non sequitur: do you have any idea how tough it is to find a photo of Paris where she's NOT scantily clad and in some overt sexual post?) Like House, Jongleur is ascribing qualities of perfection to the image in his mind called "Paris Hilton," which most likely bears little relation to the actual woman. S'okay, it's kinda cute. And frankly, women do this, too, with their objects of infatuation. Infatuation makes everyone temporarily stupid. I say "poor Jongleur," because he can wave about his intellectual prowess in front of Ms. Hilton all he wants -- she's stll not going to go out with him. Not unless he's also the heir to a small fortune, or looks like Adonis.

I had seen a video demonstrating this experiment on Stumpleupon and have been fascinated ever since.

It is nice to find someone who writes as well as you about what most people might consider boring. Thanks for taking the time to share your knowledge with us.

Those who've read QED by Feynman have enjoyed his description of how complicated a thing is actually taking place in the instance of "simple" reflection of an image in a mirror. Imagine what he'd do with Whatsernames see-through blouse?

Nice post, Jennifer! Your explanation is perfectly suitable for this layperson. Of course, further elaborations are appreciated too. : )

OT, about your reference to the last House episode in your comment -- I missed the majority of the show (wah!). Did House decide to fire her, or did he give her another chance?

"Then again, when's the last time Larry King bothered to interview a quantum physicist?"
Hmmm, maybe not Larry King, but Charlie Rose interviewed Lisa Randall, a particle

logicnazi wrote:

3) The position/momentum of elementary particles are not uncertain. These properties just don't apply to wavefunctions.

OK then. How, please to reconcile what you just said with Heisenbergs Uncertainty Principle. You can't have it both ways, you know. Wavefunctions may be the greatest thing since buttered toast, but.......

please explain how they solve the problem of position/momentum rather than saying they simply don't apply.

Evidences please.

M. L.

Hi Jennifer,

Is nothing about physics or something like that. I'm just came here to say that a used this Paris Hilton picture in my blog. You can see, my twisted version of this amazing picture here:
The text are in Portuguese, but I guess you will easily understand!


Ah yes, the photon. A little bit of space, a pinch of time and some energy. How does it manage to cross the universe remaining always in the present? Why can't we sense the present in the present of an event?

I am just an unschooled retired truck driver, so I ask your indulgence if my comments are out of line.

Mr. Einstein said that all things are relative, then tried to explain the behavior of all things with rigid rules. What if the laws of action are relative to the environment? It seems to me that QM is trying to explain the observed quantum behavior using the rules established for our relative size and speed in the universe.

If you could extrapolate the rules, taking into consideration size, speed, temperature, and so forth, I believe you could eliminate the many paradoxes and conundrums that abound in the science of both large and small, fast and slow. After all there are no true paradoxes, just flawed logic.

If I'm in the wrong ballpark, please have mercy. I just happened to Stumble in here.

According to Ben Wien, there is no debate over wave or particle. Photons are wavicles, explained in his "encyclopedia":

Someone (everyone?) missed the question above about how can two somethongs be a fraction of any measuring unit apart. I.E. can they be 1/7" apart? I think this is just an abstract question, but it would be interesting to hear some learned folks explain it. Thanks.


Below subatomic, the particles
slip through Heisenberg’s uncertainty nets.
They cannot even be called articles;
they’re just mathematical epithets.
Though we may say they have up or down spins
(we may even find them charming or strange),
like angels that dance on the heads of pins,
it takes metaphysics to find their range.
They have no shape we can define, except
as bleary fields of energy. Until
we measure them, there’s no place where they’re kept;
their locus is totally vibratile.
They pluck at space like an instrument string,
at this scale. Quark! The hadron angels sing!

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    Physics Cocktails

    • Heavy G
      The perfect pick-me-up when gravity gets you down.
      2 oz Tequila
      2 oz Triple sec
      2 oz Rose's sweetened lime juice
      7-Up or Sprite
      Mix tequila, triple sec and lime juice in a shaker and pour into a margarita glass. (Salted rim and ice are optional.) Top off with 7-Up/Sprite and let the weight of the world lift off your shoulders.
    • Listening to the Drums of Feynman
      The perfect nightcap after a long day struggling with QED equations.
      1 oz dark rum
      1/2 oz light rum
      1 oz Tia Maria
      2 oz light cream
      Crushed ice
      1/8 tsp ground nutmeg
      In a shaker half-filled with ice, combine the dark and light rum, Tia Maria, and cream. Shake well. Strain into an old fashioned glass almost filled with crushed ice. Dust with the nutmeg, and serve. Bongos optional.
    • Combustible Edison
      Electrify your friends with amazing pyrotechnics!
      2 oz brandy
      1 oz Campari
      1 oz fresh lemon juice
      Combine Campari and lemon juice in shaker filled with cracked ice. Shake and strain into chilled cocktail glass. Heat brandy in chafing dish, then ignite and pour into glass. Cocktail Go BOOM! Plus, Fire = Pretty!
    • Hiroshima Bomber
      Dr. Strangelove's drink of choice.
      3/4 Triple sec
      1/4 oz Bailey's Irish Cream
      2-3 drops Grenadine
      Fill shot glass 3/4 with Triple Sec. Layer Bailey's on top. Drop Grenadine in center of shot; it should billow up like a mushroom cloud. Remember to "duck and cover."
    • Mad Scientist
      Any mad scientist will tell you that flames make drinking more fun. What good is science if no one gets hurt?
      1 oz Midori melon liqueur
      1-1/2 oz sour mix
      1 splash soda water
      151 proof rum
      Mix melon liqueur, sour mix and soda water with ice in shaker. Shake and strain into martini glass. Top with rum and ignite. Try to take over the world.
    • Laser Beam
      Warning: may result in amplified stimulated emission.
      1 oz Southern Comfort
      1/2 oz Amaretto
      1/2 oz sloe gin
      1/2 oz vodka
      1/2 oz Triple sec
      7 oz orange juice
      Combine all liquor in a full glass of ice. Shake well. Garnish with orange and cherry. Serve to attractive target of choice.
    • Quantum Theory
      Guaranteed to collapse your wave function:
      3/4 oz Rum
      1/2 oz Strega
      1/4 oz Grand Marnier
      2 oz Pineapple juice
      Fill with Sweet and sour
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    • The Black Hole
      So called because after one of these, you have already passed the event horizon of inebriation.
      1 oz. Kahlua
      1 oz. vodka
      .5 oz. Cointreau or Triple Sec
      .5 oz. dark rum
      .5 oz. Amaretto
      Pour into an old-fashioned glass over (scant) ice. Stir gently. Watch time slow.