Moving light bulb sphere of photons

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Discussion Overview

The discussion revolves around the behavior of photons emitted from a moving light bulb and how they are perceived by an observer inside the light bulb and by external observers. It explores concepts related to the propagation of light, the shape of the wavefront, and the implications of relativistic effects such as Doppler shifting and relativistic beaming. The scope includes theoretical reasoning and conceptual clarification regarding the nature of light in different reference frames.

Discussion Character

  • Exploratory
  • Technical explanation
  • Conceptual clarification
  • Debate/contested

Main Points Raised

  • Some participants propose that an observer inside the moving light bulb would see an expanding sphere of photons, while others argue that the shape may not be a perfect sphere due to the bending of light based on the angle of emission relative to the direction of motion.
  • One participant asserts that photons traveling perpendicular to the direction of travel will bend more than those traveling parallel, leading to a skewed shape rather than a sphere.
  • Another participant emphasizes that the speed of light is constant in all reference frames, suggesting that the wavefront remains spherical despite relativistic effects like Doppler shifting and amplitude changes.
  • Mathematical transformations are presented to illustrate how the equation of a sphere of light holds in both stationary and moving frames, reinforcing the idea that the wavefront remains spherical.
  • Several analogies, such as the spokes of a wagon wheel, are used to illustrate the concept of light propagation and the implications of bending, with some participants questioning the validity of these analogies in representing the situation accurately.

Areas of Agreement / Disagreement

Participants express differing views on whether the emitted photons form a perfect sphere or a distorted shape. While some agree on the constancy of the speed of light, others challenge the implications of this constancy on the shape of the wavefront, indicating that the discussion remains unresolved with multiple competing views.

Contextual Notes

Limitations include assumptions about the medium inside the light bulb and the effects of relativistic phenomena on the perception of light. The discussion also hinges on the interpretation of mathematical transformations and analogies used to explain the behavior of light.

  • #31
matheinste said:
Hello Dreads.

Think of it this way. The centre of the expanding sphere of photons is at rest in EVERY frame. So for ANY observers present at the point of emission, no matter what their relative velocities, the expanding sphere of photons behaves as if any and all of the observers are, and remain, central to it. It is non intuitive and makes no "common sense" but it is due to the speed of light being the same in all inertial frames and is at the very heart of relativity.

Matheinste

is this for real ?

so what you are saying is if we have three observers, OB1, OB2 (and OBkenobee3 sorry couldn't resist that) Ob3 tarvelling along the x, y and z axis and they all intersect at T0 at the origin of a cartersian coor sys. At the origin is a light bulb that turns on at T0

Ob1 is traveling at seed 1 km/h, 0b2 at 0.5 C and ob3 at c what you are saying is that they will all see the same a sphere of photons expanding outwardly in all directions and each observer will percieve themelves at the centre of the sphere?
 
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  • #32
sorry I am a hopeless speller, can't spell striat :)
 
  • #33
Dreads said:
is this for real ?

so what you are saying is if we have three observers, OB1, OB2 (and OBkenobee3 sorry couldn't resist that) Ob3 tarvelling along the x, y and z axis and they all intersect at T0 at the origin of a cartersian coor sys. At the origin is a light bulb that turns on at T0

Ob1 is traveling at seed 1 km/h, 0b2 at 0.5 C and ob3 at c
What are these speeds relative to? The light bulb, perhaps? Keep in mind all speeds are relative in SR. Also, if OB3 is traveling at c, then OB3 does not have his own inertial rest frame, because the only valid inertial frames are ones moving slower than light--maybe we could modify the example so that OB3 is traveling at 0.99c relative to the bulb?
Dreads said:
what you are saying is that they will all see the same a sphere of photons expanding outwardly in all directions and each observer will percieve themelves at the centre of the sphere?
As long as they are inertial observers moving slower than light, then yes, in each of their own inertial rest frames they will remain at the center of the sphere of photons.
 
  • #34
Dreads said:
is this for real ?

so what you are saying is if we have three observers, OB1, OB2 (and OBkenobee3 sorry couldn't resist that) Ob3 tarvelling along the x, y and z axis and they all intersect at T0 at the origin of a cartersian coor sys. At the origin is a light bulb that turns on at T0

Ob1 is traveling at seed 1 km/h, 0b2 at 0.5 C and ob3 at c what you are saying is that they will all see the same a sphere of photons expanding outwardly in all directions and each observer will percieve themelves at the centre of the sphere?

Absolutely correct, except that no observer can travel at c. If we allow that observer to travel at nearly c, then the speed of light is c in all three frames. Therefore, each observer observes a sphere of photons, centered on himself, expanding at speed c.
 

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