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2

In general Allen variance is not a good way to characterize non-harmonic processes and processes which modulate the phase, frequency or amplitude of the oscillator in a non-stochastic manner for the same reason that the conventional variance is not a good measure for processes that do not, at least approximately, follow a normal distribution. For practical ...


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For a given amount of resistance (combined resistance of all the circuits in your computer, or home, or city), the amount of current which flows is proportional to the voltage. (I=V/R) When lightning strikes a line, it induces a voltage spike. Traditional circuit breakers are current-sensing devices (whether solid state or electromechanical). So, a ...


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As is pointed out in the comments, it isn't possible for an object with a non-zero (rest) mass to travel precisely at the speed of light. However, it is possible to meaningfully talk about the behavior of a clock on a ship in the limit of the ship's (constant) speed approaching the speed of light. The equation for time dilation due to relative velocity is ...


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No. At the speed of light special relativity predicts that in both reference frames the object will have the speed of light. So from outside of your ship you are moving at velocity c.


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Some cases with examples from my field (just because I know it best), but are applicable to others: Be aware of the observables. They provide starting and ending points for a theory. An example, if you are modelling 3D structure of proteins, you may be interested in generating contact maps (basically, all the pairs of atoms that are close to each other) ...


1

For a capacitor, the voltage across must be continuous since the current through since $$i_C = C \frac{dv_C}{dt}$$ Since the current through is proportional to the time derivative of the voltage across, the $v_C(t)$ must be differentiable, i.e., there can be no discontinuous change. There is no such limitation on the capacitor current, the direction ...


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When the current stops, the magnetic field inside a conducting loop diminishes, this produces an Electromotive force ($\nabla \times E=-\frac{\partial B}{\partial t}$). This force can be looked as "resisting" the changing magnetic flux field and producing a current to counter it.


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Here's a reason that hasn't been touched yet (but is alluded to by your question): to be able to form new theories. A lot of the most interesting theories in physics comes from someone reading about an experiment and trying to explain the results. We wouldn't have relativity if Einstein didn't read about the Michelson–Morley experiment and going "hmm.. ...


2

The activity of a radioactive source is measured (SI units) in Bq - Becquerels. One Bq = 1 disintegration per second. Frequently you will see the Curie (Ci) which is $37 \cdot 10^9 Bq$. The energy of radiation depends on the decay scheme. For example, for Cs-137 you find (source: ...


2

As noted in the comments the count rate is (to first order) proportional to the activity: $$ \text{rate} = k \cdot \text{activity} \,.$$ The constant of proportionality is $$ k = \text{acceptance} \times \text{efficiency} \times \text{fractional live time} \,,$$ where acceptance is a geometric factor, quantum efficiency is a property of the detector and ...


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I don't know if it helps, but perhaps breaking down what can be verified into what are the measurable quantities might be of some help? Perhaps also within what bounds the quantities from the model are valid. I must admit as a failed physicist (I think at all levels) to me theoretical physics is perhaps is more applied mathematics in the sense that ...


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For me, an experimentalist, the number of theoretically inclined people I have observed here, who are floundering with concepts that should be philosophy and who navel gaze about collapse of wavefunction, amazes me. I would order a course in particle physics, this will give an intuition of what it means to move in the quantum mechanical dimensions, a ...


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Because otherwise you are a mathematician. The point of Physics is to describe the nature using the language of maths, but the only ways to stay in contact with nature is to interact with it through experiments and observations. If you completely lose the ability to grasp how a process starts and develops, how much it can be influenced by external ...


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As a theorist, one likes to invent new ideas of how things might work. One crucial component to theory-building is searching the connection to experiments: A theory is physically meaningless when we cannot test it, for then it cannot be falsified. A theorist should be able to come up with experimental tests for his theories. This requires a good ...


2

I recall that there was a spate of neutron interferometer experiments some years ago. Google helped me find this review paper from 1988. Search terms: Young's experiment with neutrons. (Rev. Mod. Phys. 60, 4, p. 1067, 4 October 1988.)


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I would suggest 'Single- and double-slit diffraction of neutrons" by Zeilinger, Gahler, Shull, Treimer, and Mampe, Reviews of Modern Physics 60(4), 1067-1073 (1988). If I might quote the abstract: The authors report detailed experiments and comparison with first-principle theoretical calculation of the diffraction of cold neutrons ($\lambda \approx$ 2 nm) ...


1

Neutron diffraction from crystals. It's not an exact parallel, of course because it is more like a "many slit" experiment and it is reflective rather than transmissive, but the physics is the same. It is worth noting that the best diffraction spectrometer tend to also be reflective rather than transmissive simple because that avoids chromatic aberration ...


6

There is a much better description here of Fizeau's nineteenth century experiment. Some of the key features that enabled Fizeau to succeed: A lens to collect the light from the source A collimating lens to prevent the light diverging during its journey A large diameter beam to minimise broadening of the beam by diffraction More lenses to focus the light ...


1

You may be aware that both torque and angular momentum can be represented as a vector - and that such vectors follow the normal rules of vector addition. Thus, if you have equal rotation about both the X and the Y axis, what you really have is rotation about the XY axis; and in general, rotation about an arbitrary axis can be projected onto the X, Y and Z ...


2

Tungsten has been known to bait gold bars (historically). There are a few methods we use to determine if something in front of use is gold or if it is alloyed, or if its plate, fill or scrap. You can cut the bar in half...You will then know immediately of you got bunk gold. You can do a specific gravity check of your gold. There are scales designed for ...


3

(Skip to the bottom for a list of classical and quantum-mechanical effects of gravitation that have been observed in subatomic particles; my attempt to explain quantitatively what it would take to measure atom-atom gravity got longer than I'd intended, and I haven't had time to shorten it yet.) Let's suppose you want to measure the gravitational attraction ...


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Measure the gravitational attraction between two atoms? Heavens no. That's such a tiny, tiny attraction. The atoms will be attracted to themselves gravitationally, but only minutely. They'll be attracted gravitationally much more strongly to the Earth, to the lab setup and measuring equipment, to the buildings around the measuring equipment, and even to the ...


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Groups in Seattle, Colorado, and perhaps others managed to measure and verify Newton's inverse-square law at submillimeter distances comparable to 0.1 millimeters, see e.g. Sub-millimeter tests of the gravitational inverse-square law: A search for "large" extra dimensions Motivated by higher-dimensional theories that predict new effects, we ...


2

The algorithms used are as many as the experimental setups times the detectors used in the setups. They are built to fit the detectors and not the other way around. The common aspects are a few 1)charged particles interact with matter ionizing it and one builds detectors where the passage of an ionizing particle can be recorded. It can be a bubble ...


1

Well, if you have the time... CERN has all the technical design reports for its detectors online at http://cds.cern.ch/. They are excellent reading material. Start with a search for "ATLAS technical design report" and "CMS technical design report" and work your way trough the references in those documents. Once you understand the geometry of the detectors ...


0

If I understand correctly, Alice and Bob generate an entangled pair of photons and each take one. Alice does something with hers (you specified a quantum eraser experiment at a particular time, but I won't make that assumption) while Bob does a standard double-slit experiment with his. A minor point here is that with one photon you'll never get interference ...


2

It is well-known (but surprisingly hard to find a good reference for) that the probability of a photon being transmitted through some device is the fraction of the incident power of the classically transmitted through it. (See, for example, here). If you first create a linearly polarized wave/photon beam by sending it through a linear polarizer, and then ...


1

Never mind cost in dollars, it costs more in energy. Assume you had perfectly efficient pumps. To create a vacuum you have to push the air out of your chamber, if we assume we want $1 \text{ L}$ of vacuum, this takes $$ W = PV = (1 \text{ atm}) (1 \text{ L}) = 10^9 \text{ erg} $$ of work. But if you want to get your vacuum from space, even assuming you ...


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Probably not. One problem is outgassing: http://en.wikipedia.org/wiki/Outgassing#Outgassing_in_a_vacuum Even if you built an airtight container, took it out into space, opened it to let the gas out, sealed it, and brought it back to Earth, you would still have the vacuum destroyed by outgassing. Small atoms trapped in the material of the container itself ...


2

To make a long story short - Yes, it is possible, but you would have no practical reason to do it. To make a long story long, read on. While space is not a perfect vacuum, like you stated, it is close, and many applications of earth-generated vacuums are for simulating the conditions of outer space. In theory, one could put a pressure vessel in a orbital ...


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A lot of things are possible if you want to throw a lot of money at it. Is it practical? No. First, I would estimate that a rocket would be thousands of dollars. Low Earth orbit would get you the high range ($10^{-6}$ torr), high Earth orbit would possible get $10^{-9}$ torr. The next difficulty is to have the container returned to Earth (it needs to be ...


2

On a plot of $\Omega_\Lambda$ versus $\Omega_M$, there are three sets of observations that provide constraints: supernovae, the cosmic microwave background, and baryon acoustic oscillations. These three regions in the $\Omega_\Lambda$-$\Omega_M$ plane all have a common region of intersection, which is quite small. If they had failed to overlap, it would have ...


1

The Friedman model is derived from General relativity under the assumptions that on cosmological scales the Universe is homogeneous and isotropic. Therefor you could falsify the Friedman model by Showing that on cosmological scales General Relativity is not a valid model (well it could happen) Showing that on cosmological scales the universe is not ...


1

One simple test that directly probes the model is the consistency relation between the angular diameter distance $d_A(z)$ and the luminosity distance $d_L(z)$ $$d_L(z) = (1+z)^2 d_A(z)$$ This relation holds regardless of the content and state of the Universe. If this is found to be violated then it would be a hard blow against the Friedmann Universe as one ...


1

The key output of the FLRW metric is the scale factor $a(t)$ as a function of time. From this we can calculate the time derivative $\dot{a}(t)$ (which is what the red shift measures) then check whether or not it satisfies the equation: $$ \left(\frac{\dot{a}}{a}\right)^2 = \frac{8\pi G}{3} (\rho_{radiation} + \rho_{matter} + etc) $$ where the etc includes ...


-1

Yes. There is news relating to gravitational waves detection. FIRST News Item, May 2014, Scientific American: http://www.scientificamerican.com/article/proof-that-the-universe-inflated-rapidly-after-the-big-bang/ The image attached is purported "pattern of oscillation" in gravity waves, as reportedly derived from BICEP2. And purportedly related to the ...


0

Your question exposes the importance of defining notions in physics unambiguously and universally in terms of "How to measure?". As Einstein put it explicitly (however, referring specificly only to the notion of "simultaneity", and unfortunately only as late as 1917): "We thus require a definition of simultaneity such that this definition supplies us with ...


2

For Special Relativity (SR) i think the Michelson-Morley experiment is compatible and provides a verification of SR principle (some other formulations are also compatible with the experiment). Quantum Field Theory and especially the Dirac prediction and verification of positron is also a verification of SR (and many other expreriments in this context) For ...


-1

If u think of time as we percieve it as a fourth dimension time is actually all space and vice versa. We can only percieve the present at any time so every moment I guess is its own dimension or universe making time a record of all the space every moment in a way. The past can never be changed and the future can't be affected until it's the present. That's ...


0

The experiment on kxy has not been done yet, to my knowledge, but there are several (recent) experiments which are closely related and probe the heat flow through the edge channels of a Hall bar in the fractional regime: http://www.nature.com/nature/journal/v466/n7306/abs/nature09277.html or ...


0

When you have excited a normal mode ,both of the pendulumns will oscillate with the same frequency and will be either in phase or out of phase.I think a better method to see the normal mode will be to oscillate the point of suspension with one of the normal mode frequencies.


0

For a double pendulum there should be two normal modes. It sounds like you have done the analysis to determine the frequencies and mode shapes. If so, every motion will be of the form $x(t) =A \cos (\omega_1 t+\phi_1)+B \cos (\omega_2 t+\phi_2)$. If you fit the data to this form, you are in a normal mode if $A$ or $B$ is zero.



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