Top 5 hallmark experiments in physics

[Feldoh]

In no particular order:

1.) Fermi and has work with neutron bombardment.

2.) Rutherford's experiment which helped determine the structure of atoms.

3.) Franck-Hertz experiment which gave evidence for energy quantization of atoms.

4.) Onnes experiment with mercury at low temperatures which gave evidence of superconductivity.

5.) Rosalind Franklin and x-ray diffraction involving DNA, probably the most useful of these experiments.

 

[Danger]

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.

Oh, crap! Now I know why that seemed familiar. That was Aunt Ourgi. Not only was she the sister of an ancestor, but also the first known recipient of gender reassignment surgery. I didn't know that any record of her prior life as a man existed. It's a bit of a bummer; she had all of the good looks in the family, and never reproduced. The only thing that her brother passed down to me was a lot of hair.

 

[cesiumfrog]

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.

It's been disputed whether the experimental data was interpreted as a null result at the time. It's been disputed whether relativity was actually influenced (whether Einstein was originally aware of it). And from a modern perspective it is tautological, that is, before we can continue to celebrate that experiment we must explicitly teach students to understand distance wrongly in order to imagine a light-ruler changing length. (If we omitted the full-blown ether theory clutter from what we teach, that will make opportunity to impart more of non-discredited physics.)
Hermann Bondi discussed this in several places (incl. the book "assumption and myth in physical theory").

Instead, I nominate the experiment of atomic clocks compared after being in different places (including riding aboard a jet aircraft). This is another simple test of SR, but additionally also of GR. Moreover, the notion of subjectivity of time is surely one of the most awe-inspiring in physics.

 

[Feldoh]

It's been disputed whether the experimental data was interpreted as a null result at the time. It's been disputed whether relativity was actually influenced (whether Einstein was originally aware of it). And from a modern perspective it is tautological, that is, before we can continue to celebrate that experiment we must explicitly teach students to understand distance wrongly in order to imagine a light-ruler changing length. (If we omitted the full-blown ether theory clutter from what we teach, that will make opportunity to impart more of non-discredited physics.)
Hermann Bondi discussed this in several places.

Instead, I nominate the experiment of atomic clocks compared after being in different places (including riding aboard a jet aircraft). This is another simple test of SR, but additionally also of GR. Moreover, the notion of subjectivity of time is surely one of the most awe-inspiring in physics.

Yes the aether experiment was a failure and it might be confusing to teach it to students however it is still important. I think we're forgetting that the Michelson interferometer was created in order to carry out the experiment. This interferometer was important for other reasons than discrediting the aether. He didn't win the Nobel prize for discrediting aether, indeed, he became obsessed with the idea of the aether and Michelson spent the rest of his life looking for proof of it's existence. From the Nobel prize website:

The Nobel Prize in Physics 1907 was awarded to Albert A. Michelson "for his optical precision instruments and the spectroscopic and metrological investigations carried out with their aid".

 

[Danger]

It's been disputed whether the experimental data was interpreted as a null result at the time. It's been disputed whether relativity was actually influenced (whether Einstein was originally aware of it).

I'll take your word for that; I know of the experiment only because of an essay written by Asimov. The title, I believe, was "The Light That Failed". I wasn't kidding any of the times when I mentioned having no education. Everything that I know (or think that I know) comes from reading. I always appreciate being set straight when I'm wrong.

 

[Andy Resnick]

Instead, I nominate the experiment of [...]

I think arguments like this are pointless.

 

[DrDu]

I would like to bring Foucaults pendulum into the race for its outstanding simplicity.

 

[alxm]

The Millikan oil drop experiment.

I disagree. Which is why I pointed to his photoelectric effect experiments.

Millikan cherry-picked his data in that experiment. He was calculating the results as he went along and excluded the ones that didn't give the 'expected' result as having too large errors. Almost 2/3rds of his data was not in the final paper. I'd have been a huge scandal if he'd have been wrong.

But (AFAIK) his photoelectric effect experiments were very well done and meticulous. Perhaps because in that scenario, he was actually intent on proving Einstein wrong, not prove himself right.

Crick and Watson and DNA, probably the most useful of these experiments.

What experiment did Crick and Watson do?

 

[Feldoh]

What experiment did Crick and Watson do?

Hmm I guess you're right. I was referring to the x-ray diffraction experiment that brought them to their conclusion however looking into it I guess they just got the data from someone else.

 

[alxm]

Hmm I guess you're right. I was referring to the x-ray diffraction experiment that brought them to their conclusion however looking into it I guess they just got the data from someone else.

"Someone else" being Rosalind Franklin, whose contributions (which were essential) were downplayed strongly by Crick and Watson. She'd likely have shared the Nobel with them if her life hadn't been tragically cut short. And even more distastefully, Watson wrote sexist crap about her in "The Double Helix", saying she was ugly and whatnot. Their actions towards her, and the long delay it took before she got the posthumous recognition she deserved, will forever be a big taint on Crick and especially Watson in my mind (and many other people's minds).

 

[Gokul43201]

A big one that hasn't been mentioned: Wu's beta decay experiment showing parity violation in the weak interaction - technically challenging, with mind-blowing results!