Top 5 hallmark experiments in physics

[Billyneutron]

What would you say are the top 5 "hallmark"/landmark experiments in physics?

 

[mrspeedybob]

Things fall at the same rate regardless of weight.
Light travels at a constant velocity.
Double slit experiment proving wave-particle duality.

My historical perspective on physics is limited so my my top 5 will have to be limited to 3.

 

[Dr Lots-o'watts]

A few:

Classical mechanics: Measurement of G
Electromagnetics: Faraday' induction ring/electric motor
QM: Double slit experiment, and the Stern-Gerlach experiment
GR : The 3 classical tests of general relativity

 

[Drakkith]

I find this to be an impossible task. =)

Since everything in science builds on everything before it i cannot pick out a certain 5 that i would say are the top.

 

[Andy Resnick]

Glossing over differences between experiments, discoveries, and demonstrations; recognizing that '5' is too small a number, if we only include post-Newton, then my list is:

Faraday's experiments demonstrating the relationship between electric and magnetic fields
Galvani's experiments demonstrating the role of electricity in the body
Michaelson and Morley's (failed) aether experiment
The Stern-Gerlach experiment
Strassman/Hahn's discovery of nuclear fission

Including earlier scientific experiments:

Torricelli's experiment (actually, Vincenzo Viviani's experiment) demonstrating the existence of a vacuum
Galileo's experiments on falling objects
Tycho Brahe's astronomical measurements

Edit: Ack! I can't decide between Galvani and Maiman's demonstration of a laser.

Edit#2: too much wild turkey, too early in the weekend. Galvani, not Volta.

 

[alxm]

Jean Perrin's series of experiments finally proving "the discontinuous structure of matter", i.e. atoms.
Mulliken's confirmation of the photoelectric effect.

 

[Danger]

Michaelson and Morley's (failed) aether experiment

That's the main one that I was going to mention, since it kick-started Einstein to explore relativity.
I don't think that this qualifies as an "experiment" in itself, but Marie Curie leaving a sample of radium in the drawer with a photographic plate definitely had some repercussions in the science community.
There was also something about some old dude dropping cannon balls off of the Pisa tower...

 

[Dr Lots-o'watts]

...Marie Curie leaving a sample of radium in the drawer with a photographic plate...

Controlled "experiment" or not, it's certainly a hallmark event. Many important developments involve some kind of accidents.

 

[Danger]

Many important developments involve some kind of accidents.

Agreed. Things like the radium/film incident probably happen frequently. The "science" part enters the scene when someone not only notices an effect of the accident, but pursues the matter in the form of theorizing and experimenting to determine what happened.

 

[Studiot]

Since experimentalists are called for, many great names is Physics will be absent from the list.

Prolific experimenters who struck out beyond the known wisdom of their time that come to mind are

Erastothenes - realising the Earth to be round and spinning and measuring its axial tilt and radius

Hooke - experiments in elasticity and forces

Faraday - experiments in electricity and magnetism

Curies and Becquerel - experiments in radioactivity

Crick and Watson - experimental molecular science

 

[xepma]

Some condensed matter ones:
Kamerlingh Onnes -- superconductivity in 1918
Cornell and Wieman -- Bose Einstein condensate in 1995
Grunberg -- giant magneto resistance effect in 1988
von Klitzing -- integer quantum hall effect in 1980

I like how, apart from the BEC, the measured effects were quite a suprise.

Also funny: superconductivity was discovered in 1918, yet it took 40 years until BCS theory was developed. On the other hand, the BEC was theoretically predicted 70 years before its experimental realization.

 

[Andy Resnick]

That's the main one that I was going to mention, since it kick-started Einstein to explore relativity.
I don't think that this qualifies as an "experiment" in itself, but Marie Curie leaving a sample of radium in the drawer with a photographic plate definitely had some repercussions in the science community.
There was also something about some old dude dropping cannon balls off of the Pisa tower...

IIRC is was Becquerel who first discovered radioactivity/x-rays,etc by exposing film... but point well taken- that's why I chose the discoverers of fission.

 

[Loren Booda]

The Millikan oil drop experiment. Bridges classical and quantum physics with a simple setup.

My lab partner, Thad, and I measured "e" within 1% using microscopic plastic spheres floating between two charged plates.

Thad did the lion's share of the calculations.

 

[Redbelly98]

Here are some more to consider. We learn about these (the consequences, not necessarily the experiments) so early in our education that they are often taken for granted.

Roemer's measurement of the speed of light, demonstrating it's large-yet-finite value.

Joule demonstrates the equivalence between mechanical energy and heat. A forerunner to the more general conservation of energy principle.

Charles, Dalton, Guy-Lussac -- measuring volume vs. temperature of gasses at constant pressure, suggesting an absolute zero of temperature.

 

[OmCheeto]

Cavendish and his big balls.

 

[Danger]

IIRC is was Becquerel who first discovered radioactivity/x-rays,etc by exposing film...

Quite possible. Unfortunately, my lack of formal education includes history.

 

[Redbelly98]

Well, my problem with the Cavendish experiment is that it merely determines the proportionality constant in Newton's Law of Gravitation. I think it was already accepted that it had to have some value.

Establishing that the speed of light is not infinite was an entirely different class of revelation.

 

[Andy Resnick]

Quite possible. Unfortunately, my lack of formal education includes history.

If I may be so bold as to steal a quote:

"The aim of public education is not to spread enlightenment at all; it is simply to reduce as many individuals as possible to the same safe level, to breed a standard citizenry, to put down dissent and originality”

 

[Sakha]

I've always admired Foucalt's demonstration using the pendulum.
And Milikan's Oil drop was really creative.

 

[Danger]

If I may be so bold as to steal a quote:

"The aim of public education is not to spread enlightenment at all; it is simply to reduce as many individuals as possible to the same safe level, to breed a standard citizenry, to put down dissent and originality”

But that's no excuse for me; I'm not a Yank. Inherent stupidity isn't part of my genetic code—I've had to work for it.

 

[Dr Lots-o'watts]

Does Archimedes' bath tub count? If it isn't physics, what is it?

It's always been intriguing to me that volume was easier to measure than periphery.

 

[Danger]

Does Archimedes' bath tub count? If it isn't physics, what is it?

Marine architecture? Fluid dynamics? "Greeks Gone Wild"?

edit: Oh, hey... I just checked your bio and discovered that you're also a Canuk. I guess that my worry about the genetics barb offending you doesn't apply.

 

[Cleonis]

Erastothenes - realising the Earth to be round and spinning and measuring its axial tilt and radius

This is an off-topic comment, but I feel compelled.

In the world of Greek scholars it was regarded as certain that the Earth is spherical.

Greek scholars presented arguments such as the following to show that the Earth has to be spherical:
- When the Earth moves between the Sun and the Moon the shadow it casts is always round.
- When you travel north or south you see different constellations, consistent with a shifting horizon as you travel a spherical Earth.

Medieval scholars were equally aware of the Earth's sphericity (the reasoing reaching them mostly in the form of latin translations of texts from Arabic scholars.) The Earth's size was also known to a good degree of accuracy.

Christopher Columbus disbelieved the ancient sources. Columbus insisted on a different computation that gave a value of the Earth's circumference of about 20.000 kilometers. That was his basis for believing it to be possible to sail to India by sailing around the world. (For the rest of his life Columbus insisted that no new continent was discovered: Columbus claimed it was all parts of India.)

Columbus is one of history's greatest sailors, but arguably his reasoning is among the biggest bloopers.

 

[Cleonis]

What would you say are the top 5 "hallmark"/landmark experiments in physics?

Chronologically:

Newton's series of experiments involving dispersion of white light into a spectrum.

Newton's experimentum crucis:
He selected a particular color from the spectrum, and send that light through a second prism. The light did not disperse further. This shows that the dispersion of white light is due the fact that the white light is composed of multiple colors to begin with. It's not the impact upon the prism that shifts the color.

Newton favored a corpuscular theory of light. Waves need a medium to propagate in, particles don't.
Newton's interpretation of the corpuscular hypothesis implied that refraction can only be explained by a mechanism that has the side effect of making light travel faster in a denser medium (such as glass).

Experimentum crucis:
Young's double slit experiment, and other interference experiments performed in France, implied a wave nature of light.

Experimentum crucis:
Foucault succeeded in reaching a level of precision where he could compare the speed of light in air and through glass. He found the speed of light is faster in air.
This made any corpuscular theory untenable.Experimentum crucis:
Compton scattering, where x-rays interact with electrons in a way that can only be described in terms of particle-particle interactions.

Experimentum crucis:
Double slit setup with electrons, obtaining interference effects, confirming the de Broglie wave-length of electrons. (I haven't been able to find when the first one was conducted.)

[later edit] Diffraction of electrons in a crystal was confirmed in 1927 (de Broglie had published in 1924), in an experiment conducted by Davisson and Germer, in New York, and independently in an experiment by G.P. Thomson, Aberdeen, Scotland. [/later edit]

Experimentum crucis is of course latin for 'Crucial experiment'.
An 'experimentum crucis' is an experiment that is decisive for further developments. Two or more theories are contested candidates, and the experimentum crucis has the potential to simultaneously confirm one and disprove the others.

 

[Danger]

This is an off-topic comment, but I feel compelled.

In the world of Greek scholars it was regarded as certain that the Earth is spherical.

Greek scholars presented arguments such as the following to show that the Earth has to be spherical:
- When the Earth moves between the Sun and the Moon the shadow it casts is always round.
- When you travel north or south you see different constellations, consistent with a shifting horizon as you travel a spherical Earth.

Medieval scholars were equally aware of the Earth's sphericity (the reasoing reaching them mostly in the form of latin translations of texts from Arabic scholars.) The Earth's size was also known to a good degree of accuracy.

Christopher Columbus disbelieved the ancient sources. Columbus insisted on a different computation that gave a value of the Earth's circumference of about 20.000 kilometers. That was his basis for believing it to be possible to sail to India by sailing around the world. (For the rest of his life Columbus insisted that no new continent was discovered: Columbus claimed it was all parts of India.)

Columbus is one of history's greatest sailors, but arguably his reasoning is among the biggest bloopers.

I can't even edit the original down to a catch phrase or two, so my apologies for quoting the whole mess.
Cleonis... you do know, I hope, that Earth is not spherical. It's an oblate spheroid.

 

[Cleonis]

Cleonis... you do know, I hope, that Earth is not spherical. It's an oblate spheroid.

Danger... you do know, I hope, that Earth is not an oblate spheroid. The Earth's shape is called 'Geoid'.

http://www.csr.utexas.edu/grace/gravity/gravity_definition.html
"The geoid can be as low as 106 meters (350 feet) below the ellipsoid or as high as 85 meters (280 feet) above."

 

[Redbelly98]

The Earth's shape is called 'Geoid'.

Aha! So the Earth is Earth-shaped. Who'da thunk it?

 

[Redbelly98]

Experimentum crucis:
Double slit setup with electrons, obtaining interference effects, confirming the de Broglie wave-length of electrons. (I haven't been able to find when the first one was conducted.)

The double-slit experiement with electrons wasn't until 1961. But diffraction effects in electrons were verified much earlier; Davisson and Thomson won the Nobel Prize in 1937 for their earlier experiments.

A Young double slit experiment was not performed with anything other than light until 1961, when Clauss Jönsson of the University of Tübingen performed it with electrons[17][18], and not until 1974 in the form of "one electron at a time", in a laboratory at the University of Milan, by researchers led by Pier Giorgio Merli, of LAMEL-CNR Bologna.

(From http://en.wikipedia.org/wiki/Double-slit_experiment#Importance_to_physics )

This is surprisingly late when you think that the theoretical foundations of quantum mechanics were worked out by 1930.

 

[Danger]

Danger... you do know, I hope, that Earth is not an oblate spheroid. The Earth's shape is called 'Geoid'.

Potato, pototo... You're using a field-specific term which no one who doesn't study geology ever heard of, whereas I was using the vernacular... and I stand by my statement. Anyhow, the net result is the same in both cases—the damned thing ain't round.

 

[stevenb]

Oersted's 1820 experiment, which first linked electricity and magnetism, is worthy of mention.

Oh, and let's not forget the less well-known "Oorg of the Mountain Region" who in 47000 BC was the first human to find a magnetic rock and notice that broken pieces of it were attracted to each other.

He did not find a true practical application of his discovery, but did carry the stones in a pouch throughout his life. Ultimately, he attributed his long life to the magic of the stones which enabled him to defeat many foes, both man and beast.

 

[Danger]

Steven, do you have any citations or other references to support your assertion? I'm not denying anything out of hand, I hope you understand, but I've never heard of this Oorg dude before. "National Geographic" maybe? Smithsonian archives? Something on Discovery Channel at 4 in the morning? Anything? Help me out, man.

 

[Studiot]

I've never heard of this Oorg dude before

He was my grandson and I'll admit to being no longer young.

 

[stevenb]

Steven, do you have any citations or other references to support your assertion? I'm not denying anything out of hand, I hope you understand, but I've never heard of this Oorg dude before. "National Geographic" maybe? Smithsonian archives? Something on Discovery Channel at 4 in the morning? Anything? Help me out, man.

LOL ...

It's just a joke, of course, but I imagine someone in prehistoric times is the first true discoverer of magnetism and magnetic force. We may not know his (or perhaps more likely her) name, but that is a monumental discovery, and the first fumbling around with magnetic stones would be the first experiments in magnetism.

 

[Danger]

It's just a joke, of course

I had a sneaking suspicion tuned in that direction.
I hope that my response was in furtherance of the gag, as opposed to thwarting it. You inserted it with, dare I say, an incredibly stealthy hand. It's always a pleasure to see a professional at work.

 

[stevenb]

I hope that my response was in furtherance of the gag,

Of course.

It's interesting that the only known cave painting of the famous "Oorg of the Mountain Region" shows that he looked quite a bit like your avatar.