# Tag Info

1

I'd look at it as an energy storage vs loss situation. Take a patch of earth (square slab) and neglect rotation of the earth around its axis (days) so that the patch always faces the sun. At any time it's receiving an incident solar flux (assume constant) and emitting due to its own temperature. The slab also has some thermal mass (capturing the ground, ...

0

There are three reasons why mathematics is stated as an incomplete description of physics. I list them in order from pragmatically physical to more philosophical. Any calculation, any actual prediction of physics is based on a mathematical description that is known to be a mere approximation. You could conjecture that you have the complete list of ...

0

Whenever you come up with a theory (eg: Newtonian mechanics), it has some physical domain of validity, and then you come up with the next (better) theory (eg: relativity), and so on. This process might not have a "fixed point". At least if you had a fixed number of things to explain, then you might be able to consider iteratively simplifying it to an ...

2

You never know! That's the fun part of it. Having said that, there are a few game changers that could happen within the next years, like LHC finding signs of supersymmetry, or a positive result from a gravitational wave observatory. Then there is the search for dark matter candidates, someone may find signs of non-Newtonian gravity at short distances, there ...

4

There is already a number of good answers, but in addition let's compare LHC, the "useless" particle collider; with ITER, the path to the final solution of the humanity's energy hunger. They share technologies in the fields of superconductivity, vacuum, radio frequency, diagnostic instrumentation... the latter would probably not being constructed right now, ...

0

In the following all integrals are done over the whole real line. The only one I can give an in depth explanation for, in terms of calculation, is the free particle. $$U(x,t;x_0) = <x|U(t)|x_0> = \int dp <x|e^{-ip^2/2m\hbar}|P><P|x_0>$$ where the $P$ is a momentum eigenstate and the Dirac notation indicates a jump from $x_0$ into $P$ ...

5

You are thinking too much physics. Instead, think about how you process the physics data that is generated from the experiments. The answer is that there are not only physicists at CERN but also - and actually quite a lot - hardware and software engineers. The detectors are one huge combination of custom built hardware. From there on it continues to custom ...

13

Just to mention the latest developments brought up from neutrino science, it seems that the useless, wimpy, weakly interacting neutrinos (and their anti-neutrino sisters) can be harnessed to detect and monitor nuclear reactors anywhere in the world that violate non-proliferation agreements I remember a discussion about a really big neutrino beam that could ...

36

Places like CERN are a huge forcing function for computer science - think high performance computing, networking, data storage, etc. If my memory is correct, Tim Berners-Lee was at CERN when he started developing the WWW...

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The truth is we don't know. But when you think about it, how can we know? If we knew what technology would eventually come out of experiments like this, why would we not build that technology now? Large expensive machines like the CERN super-collider help us to further understand that laws of nature. And through understanding these laws, new technologies ...

34

In practice very little new technology results from experiments like those at CERN. While they are pushing the envelope on some things like the design of resonators, power klystrons and particle detector technology, the immediate technological return on those things is relatively small, even though one can argue that modern x-ray imaging (tomography) has ...

0

Measuring acceleration in $ly/yr^2$ and speed in $ly/yr$ does seem like a convenient choice of units. If you want to be able to express how fast the ship is going as a trivial function of acceleration and time, a way to do that that works correctly is to express how fast the ship is going by giving the ship's rapidity, instead of the ship's speed. In units ...

2

I am the author of the astronomy and physics ontology mentioned in the original question. The original purpose of that ontology was to improve search for data and articles in astronomy. The idea was to have data sets tables and individual columns in tables marked up with relevant keywords. The rows of data in astronomy are usually different astronomical ...

2

There is no theoretical upper limit. The question is whether the description has any practical use. Real-world objects will have some small deviations from the perfect sphere or cylinder shape, for which Mie theory applies. Look at the polar diagram of scattering of red light from a 10 micron water droplet. Figure 2 in ...

-3

Copenhagen is considered the de-facto interpretation of Quantum Mechanics for historical and sound practical reasons. It is the least speculative of the various interpretations (no need for a multitude of alternative Universes or interactions with consciousness or ...) and the product of much debate amongst the great minds of the time (Bohr, Heisenberg, ...) ...

1

Yes, the term "shadow" can refer also to something or (dare I say) someone that is dark, shady, inconspicuous, etc. One can also use it as a verb; to shadow someone is to follow them closely. Like "I'm having the new guy shadow me for a while until he learns how to do everything".

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Yes! Any beam that is blocked by an object will basically make a shadow. For example, the IceCube detector can see the moon's cosmic ray shadow.

1

Yes, for example a Crookes tube shows an electron shadow. The area I live (Chester, UK) is in a rain shadow.

2

1

Absolutely not. The issue is that different sciences operate at very different levels of abstraction. The tools of a high energy particle physicist are in general useless to the problems addressed by a forest ecologist, and more often than not are worse than useless. Some physicists study fluid dynamics. While quantum effects sometimes are important and ...

1

In principle, yes, everything is physics. Here's how: Depending on your proclivities, use string theory, loop quantum gravity, holography, or the Matrix to create the fundamental particles and forces and possibly spacetime. Use quantum chromodynamics (QCD) to get quarks and gluons to form into protons and neutrons. Use more QCD and quantum electrodynamics ...

1

Physics is broadly defined (in wikipedia, which puts it splendidly) as the general analysis of nature in order to understand how the universe behaves. This definition is not applicable to the other areas you have listed. Chemistry is defined as the science studying the properties, structure, composition, and interaction of matter distinct from that of ...

0

If the rider can manage to hold onto the bike and crouch as low as possible, he might be able to avoid getting ripped off the bike backwards, or have the bike flip over backwards. If he can stay on the bike and the bike stay upright, then there should be no harm at all. He and the bike will slow down due to the backwards force exerted by the parachute.

0

The current by definition is the flow of charge. Also, time and charge can be quantified infinetsimally at least when dealing with macrospcopic system. As such, a small amount of charge during a small time interval is what current it. As the system gets smaller, quantum level, current is quantized based on ballistic charge trasport. So, dealing with ...

3

I'm the developer of a project called the Physics Derivation Graph. https://sites.google.com/site/physicsderivationgraph https://code.google.com/p/physics-equations-graph/ My intention is to develop a set of derivations into a graph which would capture the current state of knowledge in Physics. Although I consider automated reasoning outside the scope of my ...

6

As most people know, "let there be light" is a famous biblical quote, from Genesis. Now, on to the teacher's shirt. Those equations on his back are Maxwell's equations. "Let there be light" is a joke, because Maxwell's equations describe electromagnetic fields, and light is a form of electromagnetic radiation, so the equations can be used to describe ...

0

As far as I know, most of an atom is vacuum. Therefore, in theory, would it be possible for me to throw a tiny stone through my window without breaking it because no matter actually collides? Any object whose size is greater than an atom cannot pass trough another similar body, because the single atoms are bonded (usally in a crystal) and form a ...

2

I will elaborate on @RedAct 's answer, to eliminate the coherence problem. Let the stone be a crystal. A crystal can be described quantum mechanically with a state function and there is no coherence problem as the positions of the atoms are defined quantum mechanically. Let the glass be of crystal too, again described by a single coherent wave function. ...

-1

I'm fairly sure that you could not throw a stone through glass without breaking it, but were you to have an incredibly accurate neutron gun, or something that shoots similar uncharged particles, you could aim between the atoms. In that case, you could have an uncharged particle pass through a window. On the topic of particles not hitting stuff, check out ...

0

When the stone gets really close to the window the electric field of the electrons in the stone's atoms will push against the electrons in the glass's atoms. That force will break the window, and there are no gaps in the field for it to slip through. I am oversimplifying some. I am ignoring quantum effects such as the Pauli exclusion principle, but unless ...

0

I guess in some limited sense it is possible, if the material of the window can "self-heal". For example, you can push objects through a bubble without destroying it (http://www.hometrainingtools.com/a/bubbles-and-surface-tension-science-projects - at the end of the article; the object should be wet). On a different note, slow self-healing is possible in ...

1

Yes if you open it :-) Joking aside... The reason why solids interact when contacted is the Pauli exclusion principle. It says that two electrons cannot fill the same place if they are in the same state. That means their energy levels are same, or more technically, their wave functions are not orthogonal. To make wave functions of the stone's electrons ...

3

The reason for a collision is not because the nucleus of the atoms in both the stone and the glass 'collide', it is because the 'empty space' is actually a manifestation of the coulomb force (because of the opposite charge of both the electron and proton). It is this force that you would need to overcome in order to throw a stone through a window without ...

0

At least according to non-relativistic quantum mechanics, it's theoretically possible for the stone to pass through the glass without breaking it via quantum tunneling. However, the probability of that actually happening with a normal-sized pebble and sheet of glass is of course so extremely small that it's utterly negligible.

-1

I think no, for the glass needs to have be thin also so that the proton passes, for there are many sheets of atoms and eventually the proton would collide in on3 of them. Glass is amorphous so you can't have regular geometry sheets through which it might pass

3

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

Humans weren't designed, they evolved in a series of small incremental modifications that each at the time imparted a little overall survival advantage. Such a method results in a effective design, but not necessarily a optimal one. This process is ongoing, and there are still modifications that could be made that would be advantageous in some ...

2

As was stated in the comments, your question can't be answered precisely. Here's my reactions, I hope it could help you : From a biological (evolution) point of view, a creature can be considered as "good" or "bad" only in a given environment. It means that there can't be a "best creature", because you will always find environments in which the "best" ...

1

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.. ...

0

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 ...

11

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 ...

18

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 ...

41

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 ...

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