## Search found 23 matches

Mon Jun 02, 2014 9:02 pm UTC
Forum: Science
Topic: Quantum computers as an engineering problem
Replies: 2
Views: 1304

### Re: Quantum computers as an engineering problem

There is some difficulty in answering the question you have asked because the problem with decoherence isn't necessarily just one of "well if be build a more isolated/better engineered qubit, then the problem would be solved." You are butting up against the laws of statistical physics from...
Sun Sep 08, 2013 9:11 pm UTC
Forum: Science
Topic: why do massless photons have momentum?
Replies: 12
Views: 5436

### Re: why do massless photons have momentum?

As was said before, talking about a photon with momentum and no rest mass is just the quantum mechanical version of an idea in classical E&M. It was realized that if EM waves can exert a radiation pressure, then in order for it to be consistent with classical mechanics, they must carry momentum....
Sat Aug 31, 2013 4:06 am UTC
Forum: Science
Topic: Advice for improving many small electromagnets
Replies: 2
Views: 2000

### Re: Advice for improving many small electromagnets

1. Use wire with less resistance
2. Magnetic field strength is proportional to number of turns of wire
3. Why are these wired in series?
Tue Jan 22, 2013 1:11 am UTC
Forum: Science
Topic: Quantum Harmonic Oscillator - Ladder Operators
Replies: 3
Views: 2603

### Re: Quantum Harmonic Oscillator - Ladder Operators

Do yourself a favor and quickly teach yourself Dirac notation (Ch. 3 in Griffiths). It makes the inner products more transparent when working with operators. Here is my solution: \left | a_- \left | \psi \right > \right |^2 = \left < a_- \psi | a_- \psi \right > Now since a_+ ^ \dag = a_-, the final...
Thu Dec 06, 2012 10:56 pm UTC
Forum: Science
Topic: Nuclear Physics in the US- Dead?
Replies: 15
Views: 4695

### Re: Nuclear Physics in the US- Dead?

Is nuclear physics in the US dead? Short answer: Yes. Longer answer: If it isn't dead, it is certainly on life support. This is due partly (as other posters have pointed out) to the funding situation, but also due to the fact that most of our questions about nuclear physics have either been answere...
Thu Dec 06, 2012 10:22 pm UTC
Forum: Science
Topic: re: The Heisenberg Uncertainty Principle
Replies: 15
Views: 4445

### Re: re: The Heisenberg Uncertainty Principle

The Heisenberg uncertainty relation is derived from non commuting operators acting on the wavefunction of a massive particle. A photon doesn't have mass in the traditional sense, or at least not in the context of the nonrelativistic Schrodinger equation. Thus, it is inappropriate in this context to ...
Sun Jun 24, 2012 3:50 am UTC
Forum: Science
Topic: Mechatronics vs Nanotech
Replies: 4
Views: 2207

### Re: Mechatronics vs Nanotech

I suppose I work in nanotechnology, seeing as my research focus is carbon nanotubes. It is a thriving field with a lot of interesting physics. I haven't heard of mechatronics before, but from looking at wikipedia, it looks like a strictly sort of engineering thing. You may encounter some new problem...
Sun Jun 17, 2012 5:13 am UTC
Forum: Science
Topic: Quantum Tunnelling in a Zener diode
Replies: 2
Views: 2536

### Re: Quantum Tunnelling in a Zener diode

My guess would be that above 5V you are simply forcing injection across the potential barrier at the pn junction. I have seen a similar effect in some p-channel semiconductor devices that I have made when I operate them under reverse bias.
Tue Jun 12, 2012 10:58 pm UTC
Forum: Science
Topic: ScienceDirect Down?
Replies: 5
Views: 1823

### Re: ScienceDirect Down?

Yeah I had the same issues.
Tue May 29, 2012 10:43 pm UTC
Forum: Science
Topic: Poll: greatest physicist ever
Replies: 47
Views: 11125

### Re: Poll: greatest physicist ever

Sun May 20, 2012 9:48 pm UTC
Forum: Science
Topic: Theoretical Physics Debate
Replies: 12
Views: 3077

### Re: Theoretical Physics Debate

BCS theory has its dissidents.
Fri May 11, 2012 4:32 am UTC
Forum: Science
Topic: Quantum Entanglement
Replies: 39
Views: 6569

### Re: Quantum Entanglement

Fri Apr 27, 2012 2:47 am UTC
Forum: Science
Topic: Quick Conceptual Spring Question
Replies: 6
Views: 2362

### Re: Quick Conceptual Spring Question

Suppose at [imath]t=0[/imath] you give your spring an initial force, so it starts accelerating in a direction along the [imath]x[/imath] axis. The restoring force of the spring is then $F=-kx.$ Hooke's law doesn't give you the instantaneous force that sets your spring in motion, "you" do.
Mon Apr 23, 2012 3:28 am UTC
Forum: Science
Topic: [questionnaire] (Ex-)Physics student(s) needed!
Replies: 4
Views: 2265

### Re: [questionnaire] (Ex-)Physics student(s) needed!

⋅ Where did you study/are you studying? ⋅ Are you specialised/planning to specialise in anything? If so, what? ⋅ When did you decide you wanted to study physics? ⋅  Why did you decide you wanted to study physics? ⋅ Have you completed or are you work...
Thu Apr 19, 2012 4:56 am UTC
Forum: Science
Topic: Hamilton, Lagrange and the Principle of Least Action
Replies: 6
Views: 5119

### Re: Hamilton, Lagrange and the Principle of Least Action

I recommend Classical Mechanics by John Taylor. He has a really good treatment of the principle of least action, and rigorously demonstrates why the principle of least action must be a valid statement. Basically what it boils down to is demonstrating that small displacements from the minimized path ...
Sat Apr 07, 2012 5:21 am UTC
Forum: Science
Topic: Basic Thermodynamics Mathematical Witchcraft.
Replies: 21
Views: 4444

### Re: Basic Thermodynamics Mathematical Witchcraft.

Now, back to being serious, I have the inability to accept things just because the math seems to look right, you should have seen me when I learned about the conservation of momentum.Am I the only one? As a previous poster mentioned, Noether's theorem is the most direct way to arrive at this conclu...
Sat Feb 25, 2012 2:30 am UTC
Forum: Science
Topic: How can I get good at nanotech
Replies: 5
Views: 2837

### Re: How can I get good at nanotech

I am a physics student who currently works in a nanotechnology laboratory. It is worthwhile to be familiar with basic concepts of solid-state physics and quantum mechanics, and have a good understanding of the impacts that density-of-state calculations have on the materials that you study. It is als...
Wed Feb 08, 2012 11:21 pm UTC
Forum: Fictional Science
Topic: Lets play nomic with the laws of physics
Replies: 4
Views: 3585

### Re: Lets play nomic with the laws of physics

The laws of motion shall now be arbitrarily governed by:
$\mathcal L = T^2 -U^2$
Fri Jan 27, 2012 7:02 am UTC
Forum: Science
Topic: What textbooks would you recommend in the following courses?
Replies: 42
Views: 7386

### Re: What textbooks would you recommend in the following cour

To be honest, I haven't spent much time with Purcell's text, it was just that my instructor referred to a couple proofs in there that I looked up, and it seemed fine. But, now that I think about it, that was at the very beginning of the semester, and he stopped doing that once we got to more advance...
Fri Jan 27, 2012 6:50 am UTC
Forum: Science
Topic: How often do you use statistics?
Replies: 25
Views: 5820

### Re: How often do you use statistics?

My background is in experimental nanotechnology and nanoscience, and as far as statistical analysis goes, my software gives me error bars, and I don't have to worry about chi-squared tests and all that stuff (honestly, if I needed a chi-squared test to determine the validity of my data, I have done ...
Fri Jan 27, 2012 6:43 am UTC
Forum: Science
Topic: What textbooks would you recommend in the following courses?
Replies: 42
Views: 7386

### Re: What textbooks would you recommend in the following cour

Griffiths is good for an intro Quantum Mechanics class (I had the option of using whatever text I wanted, so I picked that one up), but is only OK for E&M. Purcell is probably a bit better for E&M. For an intermediate level Classical Mechanics book, I enthusiastically recommend Taylor's book...
Wed Nov 09, 2011 3:10 pm UTC
Forum: Science
Topic: What are the most well funded fields in physics?
Replies: 11
Views: 3419

### Re: What are the most well funded fields in physics?

I would say experimental condensed matter is probably the way to go (not just because I am a condensed matter guy), but all of the graduate students in the lab that I work in have received employment immediately upon graduating at Intel, National Laboratories, STEM venture capital, and academic empl...
Wed Nov 09, 2011 3:07 pm UTC
Forum: Science
Topic: Why does light move at the speed it does?
Replies: 83
Views: 14548

### Re: Why does light move at the speed it does?

There's one property of the speed of light that's always confused me a little (which, admittedly, isn't all that hard!), and that's how it has the same value to an observer, no matter what relative (to the light being measured) speed they are travelling at. Example; Car A and car B are both travell...