The Most Beautiful Experiments in Physics

TheMatt writes "In this month's 'Physics World', Robert P. Crease asks the question: what is the most beautiful experiment in physics? Some criteria quoted are that it must change what people thought, must not be too complicated or expensive, and, most importantly, be within the reach of students (which leaves out Stern-Gerlach or Michelson-Morley). He also has a page at BNL reprinting the article, with a place for suggestions from the community on their opinion." I'll nominate a simple one: Foucault's Pendulum. :)

Comments

Here's an odd one...

[FortKnox]

What about Gallileo's hypothesis about the Feather and the Hammer that was proven on the (IIRC) Apollo 14 mission?

Eddington, 1919, proving general relativity

[Cally]

My vote (without reading other comments) goes to Arthur Eddington's validation of Einstein's relativity by demonstrating that the sun's gravity bent the light from nearby stars. But how do you see stars when they're right next to the sun? Good lateral thinking, very ingenious...

Re:Eddington, 1919, proving general relativity

[LMCBoy]

Yes it was.

BTW, Newtonian gravity also predicts that light will bend as it passes near a large mass (if you naively assume that a photon feels the force of gravity, despite the fact that it has no mass).

The difference is that the size of the deflection according to GR is larger by a factor of 2 than the Newtonian prediction, which is what Eddington confirmed.

double slit

[e4liberty]

wave particle duality

Re:Not necessarily physics... how about math?

[juggler314]

order from chaos? Not exactly. The Sierpinski Triangle is a great fractal, however it isn't chaos which forms it. Once you understand how the fractal is generated it's easy to show that for any given spot outside one of the "cleared" areas it will never migrate into a cleared area. Also it's very easy to show that any starting point from within a "cleared" area will quickly migrate outside never to return. The random picking of the next point only serves to show that we can use a random number in the algorithm to derive the same picture that we would get if one just kept disecting the triangle into 1/4's.

Now if you came up with some function where you were not able to predict anything at all about the placement of the next dot (in the Sierpinski we know much about the next dot - namely that it will lie on the midpoint of the line drawn to the next vertex chosen) and still ended up with some deep fractal pattern that would be pretty cool.

I remember playing around with the mandlebrot fractal too and seem to remember that it is a bit harder to predict that shape ahead of time (but I could just not be remembering right).

Here are links

[marcus]

The archive:
http://www.jsc.nasa.gov/er/seh/feather.h tml

and some old video:

http://www.jsc.nasa.gov/er/seh/feather.avi

Re:Back to Basics

[pomakis]

dropping a bowling ball and a light foam ball to demonstrate how mass is independant of gravity.

But this experiment is a bit misleading. Mass isn't actually independent of gravity. It is just extremely negligable when the second object is billions of times more massive than the object in question (like a bowling ball as compared to the Earth).

The force of gravity is proportional to the sums of the masses of the two objects in question (m1 + m2), and the Earth (m2) has a mass of 5.9736 × 10^24 kg. Try the same experiment by comparing how fast a bowling ball falls in comparison to a bowling-ball sized neutron star. (Of course, you wouldn't want to drop them at the same time, because you'd then be dealing with a three-body problem.)

OT: Eratosthenes vs. Chris Columbus: True Hero?

[GuyMannDude]

Eratosthenes accurately estimated the diameter and circumference of the earth with a stick. That's beauty.

Quite right. This beautiful experiment is explained and recreated in Carl Sagan's Cosmos series. Not only that, but Eratosthenes did this many years Before Christ. By the time that Christopher Columbus petitioned the royal court for funding for three ships to sail westward from Portugal to India, scientists already knew the circumference of the earth pretty damn well. Well enough to know there was no way in hell Columbus would ever make it. But in 1492 -- and this is still true today, unfortunately -- the intelligent advice of scientists was disregarded by the rulers were blinded by visions of wealth and power and the Queen funded Columbus' journey. Turns out, unbeknownst to anyone, that Columbus' ass was saved because there was a land mass closer than halfway. Columbus decided that since he had sailed west to get to India, and ran into some land, had indeed reached India and proclaimed the inhabitants Indians -- a misnomer which exists to this day.

Although Eratosthenes was a true genius the world hails Christopher Columbus as a hero even though his accomplishment was sheer accident. What does this tell you about how the world views science and scientists?

GMD

Re:The Pitch Drop Experiment

[blamanj]

glass also feels solid at room temperature but is actually liquid

Commonly believed but untrue. (And I don't care what your high school/college physics teacher said.)

From Journal of Chemical Education, 1989:
The glassy state resembles a liquid in having short-range [molecular] order without long-range order ,but differs in that the entire network is rigid, whereas in the liquid state enough energy is available tobreak and reform bonds continuously.

See http://www.urbanlegends.com/ for more.

WRONG! glass is NOT a liquid

[Sebastopol]

it is an amorphous solid, refer to this urban legend...

An Urban Legend

The legend usually appears in any of the following forms:

Antique windowpanes are thicker at the bottom, because glass has flowed to the bottom over time.

Glass has no crystalline structure, hence it is NOT a solid.

Glass is a supercooled liquid.

Glass is a liquid that flows very slowly.

Glass is a liquid.
The prolonged survival of this legend, chiefly among English speakers (and particularly among North Americans) is puzzling -- especially when one considers that glass and glassy materials are readily available, and one can easily verify if one can pour a gallon of glass, or drain a pint of obsidian.

Re:WRONG! glass is NOT a liquid

[Kintanon]

NO NO NO! My god you people are totally ignorant of victorian construction methods!
A. Glass does flow, over a GEOLOGIC TIMESCALE. In 200 years, a sheet of glass will not have changed as the result of normal flow.

B. Victorian windows are thicker at the bottom because their glass creation technique sucked at making thin sheets all the same size. There are gaps at the top of the windows because over time the wood SHRINKS because it wasn't pressure treated in victorian construction. This accounts for the gap and the thickness issue at the bottom.

So, yes, glass does flow, but you sure as hell aren't going to notice the effects in a 200 year old house.

Kintanon

Re:WRONG! glass is NOT a liquid

[Phanatic1a]

Glass doesn't even flow on geological time scales. Glass will not flow, period, unless it rises above its transition temperature, Tg. For plain old window glass, and in the limiting case of infinite time, Tg is over 250 degrees C. On shorter time scales, it's over 500 C.

Glass does not flow. It is an amorphous solid with a shear viscosity well, well in excess of 1014.6 Poise, placing it well, well within the solid regime. If it flowed on even geologic time scales, flow would certainly be observed in telescope mirrors and other optics that are precise down to fractional wavelengths.

Jesus. Go read the link that was posted earlier. There's nothing pisses me off like people who ignore readily available information in favor of propagating the same old misinformation.

Re:Measuring the height of a building...

[frankie]

this is probably apocryphal, but

How some stuff gets to Score: 5, I will never know. Remember folks,
Google makes all computing simple .

Re:The Pitch Drop Experiment

[Anonymous Coward]

For crying out loud, just do a search on google, and you assumption is easily falsified.

http://www.ualberta.ca/~bderksen/florin.html

http://www.ualberta.ca/~bderksen/florin.html#ant iq ue

Re:Two slit

[zeus_tfc]

Particles have a fixed position which can be determined within an error of the planck length. A single photon can exist in multiple locations simultaneously. If you want to call a photon a particle, you're seriously stretching your definition of particle.

A photon can act as either a particle or a wave, depending on how it is observed. I just read an article on this, so it is fresh in my mind.

The two slit experiment involves two streams of photons which can be individually measured each aimed at a wall. A blocking surface with two slits is places between the emitters and the wall.
If the photon detectors are on the far side of the blocking surface, a "ripple" pattern shows up on the wall, demonstrating the interference patterns of the waves.
If the detectors are places at the photon sources, detecting each photon as it is emitted, no interference pattern emerges, only two bright dots where the stream hits. This shows the particle nature of photons. The results depend on how the experiment is observed.

The really weird thing about the experiment is that it happens independant of time. Experiments have shown that the result(wave form or particle stream) can occur BEFORE the measurements occur. That how the measurement is taken can alter the past, or something to that effect. Pick up the latest copy of Discover mag, and there's an article.

Hand drawn holograms

[HighTeckRedNeck]

The most beautiful experiment has to be Newton's light slit and prism showing that white light is actually made up of many other frequencies. From there young minds can be introduced to all sorts of things such as why sticks appear to be bent when half in water and at what angle they seem to disappear. But to really get them going, help them create a hand drawn hologram. http://www.amasci.com/amateur/holo1.html

Some ideas...

[raytracer]

The Michelson-Morely experiment was important because it basically put the nail in the coffin of the idea of the aether, but measurements of the speed of light had actually been done for literally centuries before. Many of these experiments can easily be duplicated with minimal equipment today. Check out http://www.central-jersey-sas.org/projects/speed_o f_light/index.html for some details. I also believe that there was a duplicate of MM in the Amateur Scientist column of Scientific American, which you can now get on CD (well worth getting for more ideas).

From memory, some of the more interesting experiments the Amateur Scientist column include:

• Construction of a wide variety of optical instruments such as microscopes, telescopes, spectrascopes, and Schlieren systems.
  
• Dangerous projects like plasma jets, X-ray machines, solid fuel rockets and particle accelerators.
  
• Several different kinds of lasers.
  
• Foucault pendulums
  
• Observations of earth satellites
  
• Making diffraction gratings with a ruling engine.
  
• Aerodynamics experiments with small planes using water
  

Tons of goodies, all worth goofing around with. If you can't come up with some good ideas after leafing through this material, you just aren't trying.

Cloud Chamber

[Confuse Ed]

Though not particularly revolutionary, creating a cloud chamber and seeing the paths of radioactive particles is really quite amazing the first time you see it.

We did this experiement during A-Level physics, with small chambers using dry ice, alcohol and some of the small alpha and beta sources that schools are allowed to use.

A quick google seach will turn up lots of instructions for making your own, for example :

• some instructions from cornell
• or an article from Scientific America

although without a radioactive source you'll have to sit around and wait until some cosmic rays create some ionizing radiation that hits your experiment.

Incorrect!

[pq]

And of course, the problem with doing that experiment was the even for Millikan's it was only selectively filtered data points that got published.

Such a good story - it's a pity it is not true! Here's a link to David Goodstein's homepage - he's the vice-provost of CalTech - the second link on his homepage is a PDF file which should show you that the accusation is simply wrong.

Take a look - it's not long, and it's well worth it - before slandering a beautiful experiment.

Re:Measuring the height of a building...

[freuddot]

Urban legend it is:

Barometer