for questions about design, process, data, or analysis of experiments and observations.

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187
votes
11answers
25k views

What experiment would disprove string theory?

I know that there's big controversy between two groups of physicists: those who support string theory (most of them, I think) and those who oppose it. One of the arguments of the second group is ...
19
votes
8answers
3k views

What is the proof that the universal constants ($G$, $\hbar$, $\ldots$) are really constant in time and space?

Cavendish measured the gravitation constant $G$, but actually he measured that constant on the Earth. What’s the proof that the value of the gravitation constant if measured on Neptune would remain ...
485
votes
19answers
183k views

Cooling a cup of coffee with help of a spoon

During the breakfast with my colleagues, a question popped into my head: What is the fastest method to cool a cup of coffee, if your only available instrument is a spoon? A qualitative answer would ...
12
votes
3answers
1k views

LIGO flawed by the identical expansion of laser wavelength and arms in presence of a gravitational wave?

LIGO, Laser Interferometer Gravitational-Wave Observatory, is a large-scale physics experiment aiming to directly detect gravitational waves. The device measures the phase shift laser beams. If I ...
6
votes
2answers
501 views

Why propagation of uncertainty is linear?

I'm in doubt with one thing: let's imagine that we have $n+1$ quantities, $n$ of them being directly measured, and the other one being related to the first $n$ by a function $f : \mathbb{R}^n \to ...
166
votes
9answers
16k views

Why is the detection of gravitational waves so significant?

LIGO has announced the detection of gravitational waves on 11 Feb, 2016. I was wondering why the detection of gravitational waves was so significant? I know it is another confirmation of general ...
39
votes
13answers
11k views

Why is cold fusion considered bogus?

Cold fusion is being mentioned a lot lately because of some new setup that apparently works. This is an unverified claim. See for example: ...
41
votes
5answers
4k views

Scattering of light by light: experimental status

Scattering of light by light does not occur in the solutions of Maxwell's equations (since they are linear and EM waves obey superposition), but it is a prediction of QED (the most significant Feynman ...
34
votes
5answers
5k views

Why isn't Higgs coupling considered a fifth fundamental force?

When I first learned about the four fundamental forces of nature, I assumed that they were just the only four kind of interactions there were. But after learning a little field theory, there are many ...
17
votes
7answers
5k views

Experimental evidence of a fourth spatial dimension?

As human beings, we observe the world in which we live in three dimensions. However, it is certainly theoretically possible that more dimensions exist. Is there any direct or indirect evidence ...
41
votes
11answers
22k views

How did Newton discover his second law?

I've always assumed/been told that Newton's 2nd law is an empirical law — it must be discovered by experiment. If this is the case, what experiments did Newton do to discover this? Is it related to ...
12
votes
6answers
2k views

The square in the Newton's law of universal gravitation is really a square?

When I was in the university (in the late 90s, circa 1995) I was told there had been research investigating the $2$ (the square of distance) in the Newton's law of universal gravitation. ...
6
votes
4answers
686 views

Measuring extra-dimensions

I have read and heard in a number of places that extra dimension might be as big as $x$ mm. What I'm wondering is the following: How is length assigned to these extra dimensions? I mean you can ...
6
votes
2answers
679 views

What's wrong with this experiment showing that either FTL communication is possible or complementarity doesn't hold?

The assumptions are: Alice and Bob have perfectly synchronized clocks Alice and Bob have successfully exchanged a pair of entangled photons The idea is simply to have Alice and Bob perform the ...
7
votes
2answers
642 views

How quark electric charge directly have been measured?

How quarks electric charge directly have been measured when quarks never directly observed in isolation? (Due to a phenomenon known as color confinement.)
22
votes
4answers
4k views

Interpretation of “transition rate” in Fermi's golden rule

This is a question I asked myself a couple of years back, and which a student recently reminded me of. My off-the-cuff answer is wrong, and whilst I can make some hand-waving responses I'd like a ...
10
votes
5answers
1k views

Do the LIGO observations constitute proof of a black hole merger, and what happened to the black holes?

Information says that the gravitational waves, recently detected by LIGO, correspond (according to Einstein theory equations) to the effect of two black holes merging (with the masses of both black ...
3
votes
5answers
2k views

About the Ether Theory acceptance

Why was the Ether Theory refused by Modern Physics? If you please explain me, I just wanted to understand it more.
14
votes
2answers
982 views

Is there a good chance that gravitational waves will be detected in the next years?

Is there a good chance that gravitational waves will be detected in the next years? Theoretical estimates on the size of the effect and the sensitivity of the newest detectors should permit a ...
44
votes
12answers
11k views

Home experiments to derive the speed of light?

Are there any experiments I can do to derive the speed of light with only common household tools?
8
votes
5answers
3k views

What differs string theory from philosophy or religion? [duplicate]

Possible Duplicate: What experiment would disprove string theory? A hypothesis without hard evidence sounds very much like philosophy or religion to me. All of them tries to establish a ...
6
votes
3answers
617 views

Is there a way to decrease the rate of nuclear Beta decay?

In that question and its answers it was mentioned that you could trigger radioactive decay by bombarding atoms with gamma rays of the right energy level (there may be other solutions I do not know ...
45
votes
1answer
7k views

Why do earphone wires always get tangled up in pocket?

What is the reason? Is it caused by their narrow shape, the soft material, walking vibration or something else?
14
votes
2answers
6k views

How do we know that some radioactive materials have a half life of millions or even billions of years?

If a radioactive material takes a very long time to decay, how is its half life measured or calculated? Do we have to actually observe the radioactive material for a very long time to extrapolate its ...
7
votes
1answer
234 views

How does LIGO remove the effects of environmental noise?

Since LIGO is dealing with readings at nanometers, events such as vehicles driving nearby, and constant (but extremely minor) tremors of the earth can cause movement with the mirrors at nanometers. ...
14
votes
6answers
880 views

Speed of neutrinos

Everyone knows it is close to $c$, but how close? What are the recent results?
4
votes
1answer
150 views

How do we perform transverse measurements in a two level system?

In quantum mechanics any two level system can be mapped onto effective spin variables. If the system is defined by two energy levels, $|E_1\rangle$ and $|E_2\rangle$, the Hamiltonian is $$ H = ...
22
votes
1answer
3k views

How did Rømer measure the speed of light by observing Jupiter's moons, centuries ago?

I am interested in the practical method and I like to discover if it is cheap enough to be done as an experiment in a high school.
25
votes
3answers
3k views

How strong were the gravitational waves that LIGO detected at the source?

Congrats to the LIGO team on the announcement of their discovery of gravity waves! The articles I've read say that the distortion we see here is much smaller than a proton. What about at the source? ...
16
votes
1answer
284 views

If time isn't continuous, what is the best-known upper bound on the length of time intervals?

There have been several questions about whether time is continuous or not and it seems like the answer isn't currently known. I know quantum mechanics treats time as continuous and any mathematics ...
13
votes
1answer
407 views

How are neutrino beams emitted at CERN?

As far I know they come from accelerator collisions, but I have read confusing things like magnetically focused. How could neutrinos be guided magnetically if they aren't affected by the ...
10
votes
1answer
664 views

What makes us think we can actually detect gravitational waves?

This refers to the discussion about gravitational waves for the YouTube video LIGO Gravitational Wave Observatory. I have two questions: When the gravitational wave passes through the space where ...
4
votes
2answers
442 views

Have experiments ever suggested two different values to the same divergent series?

I believe to have understood that some physical experiments suggest finite values to divergent series (please correct me if I'm wrong, my understanding of these matters is limited). I heard, for ...
3
votes
2answers
853 views

Electromagnetic Momentum

My book says : The fact that electromagnetic radiation of energy carried momentum was known from classical theory and from the experiments of Nichols and Hull in 1903. This relation is also consistent ...
46
votes
7answers
8k views

What technology can result from such expensive experiment as undertaken in CERN?

I wonder what technology can be obtained from such very expensive experiments/institutes as e.g. undertaken in CERN? I understand that e.g. the discovery of the Higgs Boson confirms our understanding ...
23
votes
3answers
3k views

How do people calculate proportions of dark matter, dark energy and baryonic matter of the universe?

The Wikipedia page on dark matter mentions that the Planck mission had revealed that in our universe ordinary baryonic matter, dark matter and dark energy are present in the ratio: 4.9%, 26.8% and ...
33
votes
3answers
5k views

What is the smallest item for which gravity has been recorded or observed?

What is the smallest item for which gravity has been recorded or observed? By this, I mean the smallest object whose gravitational effect upon another object has been detected. (Many thanks to Daniel ...
35
votes
4answers
6k views

Has gravity ever been experimentally measured between two atoms?

Has there been any experiments, or are there any references, demonstrating gravity between atoms? If so, what are the key experiments/papers? Or if not, what is the smallest thing that has actually ...
23
votes
3answers
1k views

Has the gravitational interaction of antimatter ever been examined experimentally?

I know that the gravitational interaction of antimatter is expected to be the same as normal matter. But my question is, has it ever been experimentally validated? I think it would not be a trivial ...
9
votes
3answers
3k views

Why do neutrino oscillations imply nonzero neutrino masses?

Neutrinos can pass from one family to another (that is, change in flavor) in a process known as neutrino oscillation. The oscillation between the different families occurs randomly, and the likelihood ...
8
votes
4answers
7k views

Is Dr Quantum's Double Slit Experiment video scientifically accurate?

I'm fascinated by the fundamental questions raised by the Double Slit Experiment at the quantum level. I found this "Dr Quantum" video clip which seems like a great explanation. But is it ...
18
votes
5answers
1k views

How can I determine whether the mass of an object is evenly distributed?

How can I determine whether the mass of an object is evenly distributed without doing any permanent damage? Suppose I got all the typical lab equipment. I guess I can calculate its center of mass and ...
17
votes
5answers
19k views

How was Avogadro's number first determined?

I read on Wikipedia how the numerical value of Avogadro's number can be found by doing an experiment, provided you have the numerical value of Faraday's constant; but it seems to me that Faraday's ...
13
votes
5answers
679 views

Matter-Antimatter Asymmetry in Experiments?

As I hope is obvious to everyone reading this, the universe contains more matter than antimatter, presumably because of some slight asymmetry in the amounts of the two generated during the Big Bang. ...
10
votes
2answers
8k views

What is $p_T$? (transverse momentum?)

I've been looking at a few papers in experimental physics (from the ATLAS collaboration, for example) and I've often run across phrases such as "high-$p_T$ electron." What exactly is $p_T$? Is it ...
1
vote
2answers
592 views

Does string theory provide quantitative experimental predictions? [duplicate]

Possible Duplicate: What experiment would disprove string theory? We carefully observe things, observe patterns and then build theories that predict. String theory is frequently ...
10
votes
4answers
1k views

How much effect does the Bernoulli effect have on lift?

I understand that the Bernoulli effect is a flawed explanation for the cause of lift, and does not cause much at all, but how much? Is there any experimental data on the force caused by the ...
10
votes
5answers
4k views

What methods can astronomers use to find a black hole?

How can astronomers say, we know there are black holes at the centre of each galaxy? What methods of indirect detection are there to know where and how big a black hole is?
1
vote
2answers
267 views

Where to find cross section data for e- + p -> p + e-?

Where to find cross section data for e- + p -> p + e-? PDG's cross section data listing does not include it.
6
votes
2answers
1k views

Evidence for quantum gravity from gravitational waves

The rumor spreads that physicists will make their big gravitational wave announcement this thursday. I am far from being an experimentalist, but I want to know if there is any chance that the ...