So, is light truly relative, or is its speed constant regardless of movement?

In summary, light from distant galaxies appears to move away from us at beyond light speed, but this does not mean that light within those galaxies moves around relative to within its own local space/time. Also, since our system is traveling around our galaxy at 30km/s, and our galaxy is apparently moving through space at 600km/s, the light on Earth would be red shifted in certain directions depending on the relative motions.
  • #1
seb7
66
0
ok, light isn't relative, or is it?

Its said that galaxy far across the universe appear to be moving away from us at beyond light speed; as since the universe is expanding all around us.

So, does that mean light within these distant galaxies moves around relative to within its own local space/time?

Also, since our system is traveling around our galaxy at 30km/s, and our galaxy is apparently moving through space at 600km/s, wouldn't light on Earth be slightly red shifted in certain directions?
 
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  • #2
seb7 said:
ok, light isn't relative, or is it?

Its said that galaxy far across the universe appear to be moving away from us at beyond light speed; as since the universe is expanding all around us.

So, does that mean light within these distant galaxies moves around relative to within its own local space/time?
If I understand correctly, the answer is 'yes'. Light always moves at c Km/s at the place it is - i.e. locally.

Also, since our system is traveling around our galaxy at 30km/s, and our galaxy is apparently moving through space at 600km/s, wouldn't light on Earth be slightly red shifted in certain directions?
Light from Earth, viewed from elsewhere could be red or blue shifted, depending on the relative motions. Also, light arriving at Earth could be frequency shifted.
 
  • #3
seb7 said:
So, does that mean light within these distant galaxies moves around relative to within its own local space/time?

As Mentz114 said, the speed of light locally is always c.

seb7 said:
wouldnt light on Earth be slightly red shifted in certain directions?

Yes. This has been observed:

http://www.astro.ucla.edu/~wright/CMB-DT.html
 
  • #4
I also think that the red shifting and blue shifting occurs because spacetime itself is expanding. c is always the same, but when spacetime "stretches", the lightwave stretches, which is what causes the red/blue shift.

If I understand correctly, you wouldn't notice this if viewing something on Earth while also standing on Earth as the "stretching" wouldn't be big enough to cause any noticeable effect.
 
  • #5
No, the Earth isn't expanding eventhough the Universe is.
 
  • #6
dauto said:
No, the Earth isn't expanding eventhough the Universe is.

Got it. Matter doesn't expand, but the space-time fabric of the Universe in which matter "sits" does, so no red shifting between two locations on Earth.
 
  • #7
Is light speed relative to our earth? if not, and since the Earth is moving, that would mean it would appear that light on Earth travels faster in one direction compared to another.

I know GPS times have to be slightly adjusted as to account for time/speed difference, but are they also offset to allow for the moving of Earth through space?

I suppose what I'm asking, what space time fabric is light relative to?
 
  • #8
Light moves at the same speed, relative to everyone. It does not travel faster in one direction than the other, regardless of the movement of Earth or anything else.

Light in a galaxy far across the universe travels at the same speed there, as it does when it reaches us.

The distance between that galaxy and Earth might increase at a rate that is faster than light, but that is because the Universe is expanding.

The speed of light does not change. It always travels at c relative to everyone everywhere.
 

What is the concept of light speed and relativity?

The concept of light speed and relativity is based on Einstein's theory of special relativity, which states that the laws of physics are the same for all observers in uniform motion. It also states that the speed of light in a vacuum is constant and is the maximum speed at which all matter and information in the universe can travel.

What is the speed of light?

The speed of light is approximately 299,792,458 meters per second (or about 670,616,629 mph). This is the speed at which all electromagnetic radiation, including visible light, travels in a vacuum.

How does the speed of light affect time and space?

According to the theory of relativity, as an object's speed increases towards the speed of light, time will appear to slow down for that object. This phenomenon is known as time dilation. Additionally, the length of objects will appear to contract in the direction of motion, a concept known as length contraction.

Is it possible to travel at the speed of light?

According to our current understanding of physics, it is not possible for an object with mass to reach the speed of light. As an object approaches the speed of light, its mass would become infinite, requiring an infinite amount of energy to continue accelerating.

What is the significance of the speed of light in the universe?

The speed of light plays a crucial role in our understanding of the universe. It has been used to measure the distances between celestial bodies and has helped us understand the behavior of light and other forms of electromagnetic radiation. Additionally, the speed of light is a fundamental constant in many equations and theories in physics, including Einstein's famous equation E=mc^2.

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