 
SI2371 Special Relativity
Conceptual problems 2013
This page contains a listing of the conceptual problems discussed in class during the 2013 course.
Lecture 1:
The principle of special relativity ...
 ... is unique for special relativity
 ... appears in special and general relativity
 ... is broken by Maxwell’s equations
 ... is not part of quantum mechanics
Lecture 2:
Which two of the following observers might consider themselves to be in an inertial frame?
 An observer in a rocket travelling at velocity v=0.99c with the engines turned off
 An observer in a rocket travelling at velocity v=0.99c with the engines turned on in a direction perpendicular to the motion
 An astronaut performing a space walk
 An astronaut on a rotating space station
Lecture 3:
Which of the following is not true?
 The sum of two (forward) timelike vectors is timelike
 The sum of two spacelike vectors is timelike
 A lightlike vector is orthogonal to itself
 Two timelike vectors cannot be orthogonal
Lecture 4:
Which statement is not universally true about the poleingarage paradox?
 The pole never touches the garage doors
 The pole is entirely inside the garage (at some time)
 The pole is short enough as seen in the garage system
 The doors do not close simultaneously in the runner’s system
What is true about the 4acceleration?
 With a given proper acceleration, an object moving with velocity v will have the same acceleration regardless of the direction of acceleration
 We do need to transform the 4acceleration to the (instantaneous) restframe of a moving object to know its proper acceleration
 The 4acceleration must always be a spacelike 4vector
 Just as velocities of physical objects have to be lower than c, the proper acceleration also has a maximal value
Lecture 5:
Which of the following processes correspond to a pure force?
 An exothermic chemical reaction’s influence on its surroundings
 The influence of the ground on an accelerating car
 The acceleration of an electron in a particle accelerator
 The collapse of a star into a black hole or neutron star
What is true about electromagnetism?
 Maxwell’s equations are not invariant under Lorentz transformations
 The electromagnetic force has a large heatlike component
 The electromagnetic force is always orthogonal to the 4velocity of a particle
 The electromagnetic field tensor has 12 nonzero independent components
Lecture 6:
A current I is passing through an overall neutral conductor at rest in S. What is true in S’, which is moving with velocity v with respect to S (parallel to the conductor)?
 The electric field is zero
 The electric field is larger than the magnetic
 The electric and magnetic fields are orthogonal
 The conductor is neutral
What two statements are true for a spacelike surface?
 The normal vector is timelike
 All tangent vectors have timecomponent zero
 There is no system where two events on the surface are simultaneous
 No event on the surface is within the lightcone drawn from another event on the surface
Lecture 7:
What is not true about the de Broglie wave describing a massive particle?
 It is timelike
 The de Broglie frequency is indpendent of the inertial frame
 The phase velocity is larger than the speed of light
 The 4frequency is proportional to the 4momentum
What is true about the relativistic Doppler effect?
 A Lorentz transformation must be performed to compute it
 An observer moving orthogonal to the source will not see a Doppler shift
 The frequency will always be higher for an observer moving straight towards the source
 A timelike wave will not experience a Doppler shift
Lecture 8:
When a rocket accelerates, the stars will seem to ...
 Gather in front of the rocket
 Become redshifted due to Doppler shift
 Gather behind the rocket
 Gather in a plane perpendicular to the rocket’s acceleration
 Become blueshifted due to Doppler shift
Which of the following reactions is possible for free particles?
 γ → e^{+} + e^{}
 p → n + e^{+} + ν_{e}
 e^{+} + e^{} → μ^{+} + μ^{}
 μ^{+} → μ^{+} + γ
Lecture 9:
In order for a reaction to be kinematically allowed, it is not sufficient that ...
 The total energy is greater than the summed mass of any created particles
 The total 4momentum squared is at least as large as the square of the summed masses of the outgoing particles
 The summed mass of the incoming particles is larger than the summed masses of the products
 Energy and momentum is conserved in the reaction
What is not true in special relativity?
 An object will be in constant rectilinear motion unless acted upon by a force.
 The 4acceleration of an object is directly proportional to the pure component of the 4force and inversely proportional to the mass of the object.
 For every force F^{μ} acting on an object, there is a counter force –F^{μ} acting on something else.
 A change in the charge of an object will lead to an instantaneous change in the electromagnetic force on other charged objects.
Lecture 10:
Which of the following statements regarding an electromagnetic wave is a consequence of using the Lorentz gauge condition?
 The electric and magnetic fields are perpendicular
 The zero component of the polarization 4vector ε^{μ} is vanishing
 The polarization 4vector ε^{μ} is orthogonal to the wave vector k^{μ}
 A polarization 4vector parallel to the wave vector is unphysical
For two fluids described by the energy tensors M_{1}^{μν} and M_{2}^{μν}, the relation ∂_{ν}(M_{1}^{μν} + M_{2}^{μν}) = 0 is corresponding to the classical concept of:
 Newton’s first law (inertial movement)
 Newton’s second law (F = ma)
 Newton’s third law (actionreaction)
 Newton’s law of gravitation (F = Gm_{1}m_{2}/r^{2})
Lecture 11:
What is not true about the energy tensor of a perfect fluid?
 The restframe is the frame with the lowest energy density
 It always has zero pressure
 It is always isotropic in the rest frame
 It can be used to describe the cosmic microwave background (CMB)
The classical interpretation of the integral
P^{ν}(t_{1})P^{ν}(t_{2}) = ∫_{t1}^{t2} dt ∫ dV ∂_{μ}T^{νμ}
is
 Newton’s first law (inertial movement)
 Newton’s second law (F = ma)
 Newton’s third law (actionreaction)
 Newton’s law of gravitation (F = Gm_{1}m_{2}/r^{2})

