User Physiks lover

11

31

votes

5

answers

7k

views

Does a photon in vacuum have a rest frame?

Jun 18 '17 at 10:31 Qmechanic♦ 132k

15

26

votes

7

answers

7k

views

Why is there a $\frac 1 2$ in $\frac 1 2 mv^2$?

newtonian-mechanics energy work

Apr 25 '19 at 9:16 Community♦ 1

2

10

votes

4

answers

771

views

Why isn't there a limit for a Euclidean rotation, as for a Minkowski rotation?

special-relativity

Jul 31 '15 at 4:18 Community♦ 1

7

votes

2

answers

637

views

What experiments compete with BICEP 2, and when are their results expected?

cosmology experimental-physics cosmological-inflation cosmic-microwave-background

Jan 31 '15 at 19:36 Art Brown 5,245

1

7

votes

8

answers

3k

views

Is Einstein's 1916 General Relativity paper a recommended way to start learning about the subject?

general-relativity

Jan 24 '13 at 12:08 Eduardo Guerras Valera 3,487

1

6

votes

1

answer

163

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Why isn't EM radiation from an accelerated charge time reversible?

electromagnetism electromagnetic-radiation classical-electrodynamics cpt-symmetry

Jan 31 at 21:03 knzhou 81.2k

2

6

votes

2

answers

317

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How does Dirac define the representative of $\{\langle\phi\frac{d}{dq}\}\psi\rangle = \langle\phi\{\frac{d}{dq}\psi\rangle\}$

quantum-mechanics operators hilbert-space

Apr 7 '15 at 19:32 Community♦ 1

2

5

votes

4

answers

1k

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Are the principles of space-time homogeneity and Isotropy independent of one another?

general-relativity spacetime symmetry differential-geometry

Nov 25 '15 at 4:38 299792458 3,054

1

5

votes

2

answers

2k

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Is (0,0,0) an undefined vector?

vectors

Nov 11 '11 at 22:41 David Z♦ 70.4k

7

4

votes

1

answer

4k

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Proofs that every professional physicist should know [closed]

soft-question big-list

Jul 18 '19 at 7:12 Qmechanic♦ 132k

3

4

votes

3

answers

1k

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Explanation for $E~$ not falling off at $1/r^2$ for infinite line and sheet charges?

electrostatics electric-fields gauss-law coulombs-law

Aug 5 '18 at 7:20 Qmechanic♦ 132k

4

votes

2

answers

3k

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Is the change in kinetic energy of a particle frame independent?

special-relativity classical-mechanics energy inertial-frames

Oct 13 '17 at 8:34 Qmechanic♦ 132k

2

4

votes

4

answers

9k

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Is the electric field zero inside an ideal conductor carrying a current?

electromagnetism electric-fields

Jul 27 '16 at 15:18 Sergei Gorbikov 849

4

votes

2

answers

107

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Should the eigenkets be weighted in $|P\rangle = \sum\limits_{r}|\xi^r\rangle$?

quantum-mechanics hilbert-space superposition

Oct 13 '14 at 10:16 Community♦ 1

4

votes

1

answer

304

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Is there a Newton's third law for the em field?

classical-mechanics classical-electrodynamics

Oct 25 '11 at 22:51 stringparser 664

1

3

votes

1

answer

108

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How can one define a covariant rate of change of rest mass for an extended body?

general-relativity special-relativity classical-mechanics mass mass-energy

Nov 5 at 7:45 Richard 983

1

3

votes

4

answers

182

views

Is there a space-like equivalent of the Twin Paradox?

special-relativity spacetime time-dilation

Oct 15 '17 at 18:01 WillO 10.1k

1

3

votes

3

answers

3k

views

Calculate relativistic boost to COM frame from two arbitary velocities?

homework-and-exercises special-relativity classical-mechanics velocity inertial-frames

Feb 12 '17 at 16:08 Qmechanic♦ 132k

3

votes

2

answers

356

views

Why does a stationary force affect the conservation of momentum, but not the conservation of energy?

classical-mechanics energy momentum

Sep 24 '13 at 17:02 Qmechanic♦ 132k

3

votes

1

answer

2k

views

Can relativistic kinetic energy be derived from Newtonian kinetic energy?

classical-mechanics special-relativity

Apr 13 '12 at 17:33 Community♦ 1

3

votes

1

answer

3k

views

Problems that Lagranges equations of the 1st kind can solve whereas the 2nd kind can't?

classical-mechanics lagrangian-formalism

Jan 19 '12 at 13:12 Qmechanic♦ 132k

1

2

votes

2

answers

94

views

Do Maxwell's equations contain any information on the time evolution of the current density $J$?

electromagnetism lagrangian-formalism conservation-laws maxwell-equations time-evolution

Jul 11 at 16:25 G. Smith 39.8k

2

votes

2

answers

90

views

QM probability density function without Born's rule, invariant to wave-function phase

quantum-mechanics hilbert-space wavefunction probability born-rule

Jul 31 '19 at 8:21 user2723984 2,626

1

2

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83

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Does a spring's $k$ affect the acceleration of a coupled mass?

newtonian-mechanics classical-mechanics energy spring

Oct 30 '18 at 23:37 Chet Miller 20.5k

1

2

votes

2

answers

78

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Must the varied paths in the action be physically possible?

classical-mechanics lagrangian-formalism variational-principle action

Oct 6 '18 at 6:44 Qmechanic♦ 132k

1

2

votes

2

answers

1k

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What coordinate systems allows the magnitude of the basis vectors to change with position?

differential-geometry vectors coordinate-systems

Aug 9 '15 at 18:38 Alfred Centauri 54.4k

2

votes

1

answer

105

views

If time-like paths are geodesics, what physical principle applies to space-like intervals?

special-relativity field-theory classical-electrodynamics variational-principle geodesics

May 27 '15 at 19:43 By Symmetry 5,994

1

2

votes

1

answer

123

views

Why does Dirac write $\langle\xi'|\overline{f(\xi)} = \overline f(\xi ')\langle\xi'|$?

quantum-mechanics notation

Oct 5 '14 at 21:33 Nikos M. 4,348

1

2

votes

1

answer

79

views

How does Dirac show that $\langle B|\bar{\bar{\alpha}}|P\rangle\;=\; \overline{\langle P|{\bar{\alpha}}|B\rangle}\;=\; \langle B|{\alpha}|P\rangle$?

quantum-mechanics operators

Sep 2 '14 at 17:16 Community♦ 1

1

2

votes

3

answers

1k

views

Must the Lagrangian always be known for the Euler-Lagrange equations to be of any use?

classical-mechanics lagrangian-formalism

Mar 16 '13 at 22:49 Community♦ 1

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73 Questions

Does a photon in vacuum have a rest frame?

Why is there a $\frac 1 2$ in $\frac 1 2 mv^2$?

Why isn't there a limit for a Euclidean rotation, as for a Minkowski rotation?

What experiments compete with BICEP 2, and when are their results expected?

Is Einstein's 1916 General Relativity paper a recommended way to start learning about the subject?

Why isn't EM radiation from an accelerated charge time reversible?

How does Dirac define the representative of $\{\langle\phi\frac{d}{dq}\}\psi\rangle = \langle\phi\{\frac{d}{dq}\psi\rangle\}$

Are the principles of space-time homogeneity and Isotropy independent of one another?

Is (0,0,0) an undefined vector?

Proofs that every professional physicist should know [closed]

Explanation for $E~$ not falling off at $1/r^2$ for infinite line and sheet charges?

Is the change in kinetic energy of a particle frame independent?

Is the electric field zero inside an ideal conductor carrying a current?

Should the eigenkets be weighted in $|P\rangle = \sum\limits_{r}|\xi^r\rangle$?

Is there a Newton's third law for the em field?

How can one define a covariant rate of change of rest mass for an extended body?

Is there a space-like equivalent of the Twin Paradox?

Calculate relativistic boost to COM frame from two arbitary velocities?

Why does a stationary force affect the conservation of momentum, but not the conservation of energy?

Can relativistic kinetic energy be derived from Newtonian kinetic energy?

Problems that Lagranges equations of the 1st kind can solve whereas the 2nd kind can't?

Do Maxwell's equations contain any information on the time evolution of the current density $J$?

QM probability density function without Born's rule, invariant to wave-function phase

Does a spring's $k$ affect the acceleration of a coupled mass?

Must the varied paths in the action be physically possible?

What coordinate systems allows the magnitude of the basis vectors to change with position?

If time-like paths are geodesics, what physical principle applies to space-like intervals?

Why does Dirac write $\langle\xi'|\overline{f(\xi)} = \overline f(\xi ')\langle\xi'|$?

How does Dirac show that $\langle B|\bar{\bar{\alpha}}|P\rangle\;=\; \overline{\langle P|{\bar{\alpha}}|B\rangle}\;=\; \langle B|{\alpha}|P\rangle$?

Must the Lagrangian always be known for the Euler-Lagrange equations to be of any use?