Question about the relative motion of an eye relative to light source

In summary, the question explores how the motion of an eye affects its perception of a light source. It examines the principles of relative motion, including how the speed and direction of the eye's movement can alter the way light is observed, potentially influencing visual acuity and the perception of brightness and color. The inquiry highlights the dynamic relationship between an observer's movement and the behavior of light, emphasizing the importance of understanding these interactions in fields such as optics and visual perception.
  • #1
Chenkel
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Hello everyone,

I've been thinking about 2nd postulate of relativity, it seems that and the Michaelson-Morley experiment seems to imply that there is no ether, but I was thinking about a special situation that doesn't seem to go against that postulate.

I think my question is basic so hopefully it makes sense and I don't make any major blunders.

Suppose there is an initial light source at distance D away from an eye and the light turns on at the start of the problem, and the eye moves with a relative velocity of v towards the light source, how long does it take light to reach the eye?

I was thinking about it and the gap seems to be closing at a rate of ##c + v## So I would expect the light to reach the eye at the time ##\frac {D} {c + v}##

If the eye is moving away from the light source at the start of the problem when it turns on at a distance D I would imagine the gap to be closing at a rate of ##{c - v}## so the time to cover the distance D should be ##\frac {D} {c - v}##

Hopefully I'm not making any major mistakes in my analysis, let me know what you think.

Thanks.
 
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  • #2
In the rest frame of the light source where the eye is moving, yes, these are the expressions. It is unclear why you think this affects the results predicted by relativity.
 
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  • #3
Orodruin said:
In the rest frame of the light source where the eye is moving, yes, these are the expressions. It is unclear why you think this affects the results predicted by relativity.
I don't think it affects the results predicted by relativity, I'm just trying to make sure I'm not making any mistakes regarding the postulates of relativity and the framework of it.
 
  • #4
Chenkel said:
I don't think it affects the results predicted by relativity, I'm just trying to make sure I'm not making any mistakes regarding the postulates of relativity and the framework of it.
You have specified everything in one frame here, so the same intercept calculations you do in Newtonian physics apply. It's only when you want to do more complex physics (conservation laws or frame changes, for example) that you will find differences.
 
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FAQ: Question about the relative motion of an eye relative to light source

How does the relative motion of an eye with respect to a light source affect the perception of light?

The relative motion of an eye with respect to a light source can affect the perception of light through the Doppler effect, which changes the frequency and wavelength of light. If the eye is moving towards the light source, the light waves are compressed, resulting in a blue shift (higher frequency). If the eye is moving away from the light source, the light waves are stretched, resulting in a red shift (lower frequency).

What is the Doppler effect in the context of light and how does it relate to the relative motion of an observer?

The Doppler effect in the context of light refers to the change in frequency (and consequently wavelength) of light due to the relative motion between the light source and the observer. When the observer moves towards the light source, the light waves are compressed, leading to a blue shift. Conversely, when the observer moves away from the light source, the light waves are stretched, leading to a red shift.

Can the human eye detect the Doppler shift in visible light due to relative motion?

The human eye is generally not sensitive enough to detect the Doppler shift in visible light due to relative motion under normal circumstances. The shifts in frequency are typically too small to be noticeable without precise instruments. However, significant relative velocities, such as those encountered in astronomical observations, can produce measurable Doppler shifts that can be detected with specialized equipment.

How does the speed of the observer relative to the speed of light affect the observed color of the light source?

The speed of the observer relative to the speed of light affects the observed color of the light source through the relativistic Doppler effect. If the observer moves at a significant fraction of the speed of light towards the source, the light appears bluer (blue shift). If the observer moves away at a significant fraction of the speed of light, the light appears redder (red shift). These effects are much more pronounced at relativistic speeds, close to the speed of light.

What practical applications rely on understanding the relative motion of an eye or detector to a light source?

Several practical applications rely on understanding the relative motion of an eye or detector to a light source, including astronomical observations, radar and lidar systems, and Doppler radar used in weather forecasting. In astronomy, measuring the Doppler shift of light from stars and galaxies helps determine their velocities and distances. In radar and lidar, Doppler shifts are used to measure the speed of objects. Doppler radar in meteorology helps in determining the speed and direction of precipitation and wind.

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