Does light only travel at one speed?

Megahurtz400

Megahurtz400

Megahurtz400

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Just watched Wonders of the Solar system and had a discussion with my dad about stars in the Galaxy dying.

Say "Beetlejuice" (Around 600 light years away) was to die now, would we not see it for 600 years?

My idea is that light can only travel at one speed as it has no resistance, so therefore it would take 600 years for the first bit of light made in the process of the star dying to get to our eyes?

No idea if thats right or not though :D

Any ideas?
 
For all intents and purposes, yes.

When looking at the night sky, everything you see is in the past. The light from the nearest star outside the solar system takes just over 4 years. Stuff further away takes longer.
 
No, it goes slower through glass and stuff. It travels at a constant speed in a vacuum, which we call the speed of light afaik.
 
Its speed varies depending on the medium that it is travelling through.

The universal constant c is the speed of light in a vacuum.
 
Unless passing through a medium. then it can slow down.

Light slows down when passing through the glass in your window for example. When it emerges the other side it speeds up again.
 
as above, :)

I takes 8 minutes or something for light from the sun to reach us? I'm sure I was told that in science.
 
Ahhhh I see :)

I used an example of my hand moving through water:

My hand moves slower through water because it has mass and resistance.

To the best of my knowledge, light doesnt have mass as it is energy, therefore it can't have any resistance.

But I take it I was wrong haha xD
 
Megahurtz400 said:
Just watched Wonders of the Solar system and had a discussion with my dad about stars in the Galaxy dying.

Say "Beetlejuice" (Around 600 light years away) was to die now, would we not see it for 600 years?

My idea is that light can only travel at one speed as it has no resistance, so therefore it would take 600 years for the first bit of light made in the process of the star dying to get to our eyes?

No idea if thats right or not though :D

Any ideas?
Click to expand...

While light's speed and direction can be affected by specific mediums such as Glass, and forces such a mavity (the Variable Speed of Light), it has a constant speed in a vacuum (the Effective Speed of Light) so in essence it would take 600 years for the event to be seen from Earth.

The Sun for example is always seen 8 minutes behind it's true position due to the fact that light takes 8 minutes to travel the distance.
 
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Technically speaking light waves don't really slow down. It is just an apparent affect caused by atoms absorbing photons and re-emitting them. This lag causes the wavefront to be held back or even advanced [plasma can "speed up" light].

Source: The Internets.
 
Megahurtz400 said:
My idea is that light can only travel at one speed as it has no resistance, so therefore it would take 600 years for the first bit of light made in the process of the star dying to get to our eyes?
Click to expand...
It's more than just 'no resistance', its that light travels at the same speed regardless of your inertial motion, unlike other objects.

Suppose you have a gun and suppose you also have a target which can measure the speed of bullets which it it. You stand still and point the gun and fire and the target gives a read out of 1000kph. Suppose you get in your car and drive towards the target at 100mph and fire again. The target will read out 1100kph.

But what if you do this with a laser? Stand still and fire your laser at the target and it'll read 300,000 km/s. Now you get in your car, which happens to have a top speed of 100,000 km/s, get to top speed and fire your laser. What does the target say? It'll say 300,000 km/s! Doesn't matter if you're driving at the target, away from it, around it in a circle, it'll be 300,000 km/s.

That is what it means to say "The speed of light in a vacuum is 300,000km/s". In the case of planets or rocks or bullets the speed you measure is dependent upon your motion. If you drive a car at 40 mph (which is measured relative to the ground) you'll overtake someone driving at 10mph at a relative speed of 30mph. However, if you both turn on your headlights then someone further down the road will measure the speed of the light particles coming from each of you to be precisely the same. Hence why the speed of light in a vacuum is well defined without reference to anything else, it is independent of the motion of the emitter and the detector (up to subtle things to do with non-inertial motion).

Castiel said:
While light's speed and direction can be affected by specific mediums such as Glass, and forces such a mavity (the Variable Speed of Light)
Click to expand...
To what are you referring?
 
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Castiel said:
The Sun for example is always seen 8 minutes behind it's true position due to the fact that light takes 8 minutes to travel the distance.
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Something I've always liked is the fact if the sun suddenly died, it'd take us 8 minutes to even know. That's all, 8 minutes.

/gonna be paranoid for the next 8:01 mins.
 
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