Why is the speed of light constant and independent from the observer?

In summary, the speed of light is constant and independent from the observer because of Lorentz invariance, which is a property of the fundamental laws of physics. The reason for this remains a philosophical question, as it cannot be answered solely by physics.
  • #1
redphoton
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Why is the speed of light constant and independent from the observer?
 
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  • #2
The philosophy department is down the hall. ;)
 
  • #3
Well, it's constant if you stick to inertial reference frames whose coordinates are related to one another by the Lorentz transformation, and relativity predicts (and all the evidence suggests) that the fundamental laws of physics all have the property of "Lorentz invariance" which means they obey the same equations when written in any inertial coordiante system of this type. There's nothing stopping you from using a non-inertial coordinate system where light's speed is different, though.

As for "why", it depends what you're asking...given inertial frames related by the Lorentz transformation, it's easy to show that anything with a coordinate velocity of c in one inertial frame will have a coordinate velocity of c in any other inertial frame. But as to why the the laws of physics are invariant under the Lorentz transformation in the first place, like ZikZak says that seems to be more of philosophical question.
 
  • #4
I wouldn't say it's a philosophical question. Philosophy doesn't seem to have anything to do with it (unless you're going to study the meaning of the word "why" or something like that). The only thing that could answer it is another theory of physics. Of course, if we ever find a theory that answers that question, it would give us a new set of "why?" questions.
 
  • #5
Fredrik said:
I wouldn't say it's a philosophical question. Philosophy doesn't seem to have anything to do with it (unless you're going to study the meaning of the word "why" or something like that). The only thing that could answer it is another theory of physics. Of course, if we ever find a theory that answers that question, it would give us a new set of "why?" questions.
It's philosophical in the sense that if Lorentz-invariance is part of the most fundamental laws (the final 'Theory of Everything') rather than being derivable from more fundamental laws, then "why are the laws of physics Lorentz-invariant" is just a subset of the general question "why are the laws of physics what they are", which obviously cannot be answered by physics and therefore is a metaphysical question (for example, one answer might be 'because God chose them that way', another might be 'because all mathematically describable universes exist as Platonic forms, and are perceived as real by any intelligent beings that evolve within them').
 

1. How was the speed of light first measured?

The speed of light was first measured in 1676 by Danish astronomer Ole Rømer by observing the eclipses of Jupiter's moons. By tracking the differences in the timing of the eclipses as Earth moved closer to or further away from Jupiter, Rømer was able to calculate the speed of light to be about 220,000 kilometers per second.

2. Why is the speed of light considered a universal constant?

The speed of light is considered a universal constant because it is the same in all directions and in all inertial reference frames. This means that no matter how fast an observer is moving or from what direction they are observing, they will always measure the speed of light to be approximately 299,792,458 meters per second. This has been confirmed through numerous experiments and is a fundamental principle in physics.

3. How does the speed of light being constant affect our understanding of time and space?

The constancy of the speed of light is a crucial component of Einstein's theory of relativity. It means that the laws of physics are the same for all observers, regardless of their relative motion. This has profound implications for our understanding of time and space, as it suggests that time and space are not absolute but are instead relative to the observer's frame of reference.

4. What is the significance of the speed of light in modern physics?

The speed of light plays a critical role in modern physics, as it is a fundamental constant that appears in many equations and theories. For example, it is a key component in Einstein's famous equation E=mc², which represents the relationship between energy, mass, and the speed of light. The speed of light also plays a crucial role in theories such as quantum mechanics and the study of the fundamental forces of nature.

5. Is it possible for the speed of light to change?

According to our current understanding of physics, the speed of light is a constant and cannot be changed. However, some theories, such as string theory, propose that the speed of light may have been different in the early universe. Still, there is no conclusive evidence to support this idea, and the speed of light remains a constant in our everyday observations and experiments.

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