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1500 questions
37
votes
8 answers
Gibbs free energy intuition
What is Gibbs free energy? As my book explains:
Gibbs energy is the energy of a system available for work.
So, what does it want to tell? Why is it free? Energy means ability to do work. What is so special about this energy? Can anyone simply…
user36790
37
votes
5 answers
What do we see while watching light? Waves or particles?
I'm trying to understand quantum physics. I'm pretty familiar with it but I can't decide what counts as observing to cause particle behave (at least when it's about lights). So the question is what do we see with our eye-balls?
We point a laser (or…
martintrapp
- 505
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- 6
37
votes
5 answers
What is the most efficient information storage?
What is the most efficient way to store data that is currently hypothesized? Is it theoretically possible to store more than one bit per atom?
Until Floris' comment, I hadn't considered that efficiency is dependent on what you're trying to optimize.…
Tyler
- 489
37
votes
3 answers
Deriving the Coulomb force equation from the idea of virtual photon exchange?
Since Newton's law of gravitation can be gotten out of Einstein's field equations as an approximation, I was wondering whether the same applies for the electromagnetic force being the exchange of virtual photons. Is there an equation governing the…
Meep
- 3,959
37
votes
19 answers
Why does the gas get cold when I spray it?
When you spray gas from a compressed spray, the gas gets very cold, even though, the compressed spray is in the room temperature.
I think, when it goes from high pressure to lower one, it gets cold, right? but what is the reason behind that…
Ken D
- 481
37
votes
6 answers
Motion described by $m \frac{\mathrm{d}^2 x}{\mathrm{d}t^2}=-k\frac{\mathrm{d}^{\frac12 }x}{\mathrm{d}t^{\frac12}}$
What kind of motion would a (preferably dimensionless for simplicity) body do if the force acted on it was proportional to the semi-derivative of displacement, i.e.
$$m \frac{\mathrm{d}^2…
user148432
- 515
37
votes
8 answers
Is the Big Bang defined as before or after Inflation?
Is the Big Bang defined as before or after Inflation? Seems like a simple enough question to answer right? And if just yesterday I were to encounter this, I'd have given a definite answer. But I've been doing some reading while writing up my thesis…
Jim
- 24,458
37
votes
8 answers
Interval preserving transformations are linear in special relativity
In almost all proofs I've seen of the Lorentz transformations one starts on the assumption that the required transformations are linear. I'm wondering if there is a way to prove the linearity:
Prove that any spacetime transformation…
a06e
- 3,702
37
votes
2 answers
The Impossibility ( or Possibility) of Solving $N$-Body Problem
One can obtain the solution to a $2$-Body problem analytically. However, I understand that obtaining a general solution to a $N$-body problem is impossible.
Is there a proof somewhere that shows this possibility/impossibility?
Edit: I am looking to…
Graviton
- 2,526
37
votes
7 answers
How does "warp drive" not violate Special Relativity causality constraints?
I'm talking about this nonsense: http://www.washingtonpost.com/news/post-nation/wp/2014/06/11/this-is-the-amazing-design-for-nasas-star-trek-style-space-ship-the-ixs-enterprise/
Now, I'm aware that there are problems with the practicalities (or…
Larry Gritz
- 764
37
votes
7 answers
If we suddenly lost track of time, how would we know what time is now?
If we hypothetically lost all watches and all devices that keep track of time, how would we say what is the current time? Or we actually don't and time is just a convention?
matt_zarro
- 489
37
votes
3 answers
Do photons occupy space?
Total noob here.
I realize that photons do not have a mass. However, they must somehow occupy space, as I've read that light waves can collide with one another.
Do photons occupy space? and if so, does that mean there is a theoretically maximum…
LanceLafontaine
- 799
37
votes
3 answers
What's the relationship between $SL(2,\mathbb{C})$, $SU(2)\times SU(2)$ and $SO(1,3)$?
I'm a beginner of QFT. Ref. 1 states that
[...] The Lorentz group $SO(1,3)$ is then essentially $SU(2)\times SU(2)$.
But how is it possible, because $SU(2)\times SU(2)$ is a compact Lie group while $SO(1,3)$ is non-compact?
And after some…
346699
- 5,941
37
votes
3 answers
Are the Hamiltonian and Lagrangian always convex functions?
The Hamiltonian and Lagrangian are related by a Legendre transform:
$$
H(\mathbf{q}, \mathbf{p}, t) = \sum_i \dot q_i p_i - \mathcal{L}(\mathbf{q}, \mathbf{\dot q}, t).
$$
For this to be a Legendre transform, $H$ must be convex in each $p_i$ and…
N. Virgo
- 33,913
36
votes
4 answers
The problem of self-force on point charges
Allow me to preface this by stating that I am a high school student interested in physics and self-studying using a variety of resources, both on- and off-line, primarily GSU's HyperPhysics website, Halliday & Resnick's Fundamentals of Physics,…
obataku
- 492