Can the Speed of Light Be Changed and What Does It Mean for Space Exploration?

[Nenad]

no the distance between two points would be the same no matter where you are. it would just take less time from point to point going at or near light speed.

I don't know where you learned your special relativity (if you even did ) But the distance DOES change with varying speed.

 

[pervect]

still the distance would not change.

bino, distance is not an invariant. It depends on the observer.

 

[bino]

maybe I am not understanding what your trying to say but if I am traveling in a car going 100 mph past two trees 20 feet apart from each other. then i go past again but only go 1 mph the distance between the two trees is still 20 feet

 

[pervect]

maybe I am not understanding what your trying to say but if I am traveling in a car going 100 mph past two trees 20 feet apart from each other. then i go past again but only go 1 mph the distance between the two trees is still 20 feet

If two trees are 20 feet apart when you are standing still, if you go past them at 80% of the speed of light, they are only 12 feet apart.

This is called "length contraction" and is a consequence of relativity.

see for example
http://www.glenbrook.k12.il.us/gbssci/phys/mmedia/specrel/lc.html

 

[geometer]

bino, distance is not an invariant. It depends on the observer.

Actually, this is not true. In Relativity, the distance between two space-time points is invariant. This is actually very easy to show mathematically.

And, it's not distance that contracts when you move close to the speed of light - YOU contract in the direction of your travel.

 

[pervect]

Actually, this is not true. In Relativity, the distance between two space-time points is invariant. This is actually very easy to show mathematically.

And, it's not distance that contracts when you move close to the speed of light - YOU contract in the direction of your travel.

I think you're confused. The Lorentz interval is the invariant in relativity. This is the difference of the square of the distance, and c^2 times the square of the time. Time is not an invariant. Space is not an invariant. The Lorentz interval *is* invariant. Note that the Lorentz interval along a light beam is always equal to zero.

As far as contraction goes, see the old "barn and the pole' paradox. From the point of view of the pole vaulter, the barn he's running through contracts. From the point of the view of the barn, the pole vaulter contracts.

 

[bino]

the way i read it was that i or my ship would be contracted in size not the distance between the trees

 

[Doc Al]

the way i read it was that i or my ship would be contracted in size not the distance between the trees

You have it exactly backwards.

 

[plum]

Bino you might want to do a little reading, then come back.

http://casa.colorado.edu/~ajsh/sr/sr.shtml

 

[russ_watters]

http://www.newscientist.com/news/news.jsp?id=ns99992796

From the article:

While the peak moves faster than light speed, the total energy of the pulse does not. This means Einstein's relativity is preserved, so do not expect super-fast starships or time machines anytime soon.

More on refraction: The high school explanation really gets on my nerves because it gives people the wrong idea about light - and the belief that C isn't constant interferes with later learning.

Think about the issue this way: how does light know its in a medium? What happens when light enters glass? It hits an atom. When it hits an atom in a transparent media like glass, the photon is absorbed and re-emitted in the same direction it started in. There is a delay between the absorption and re-emission that causes the appearance of a change in speed.

Since refraction depends on hitting atoms, density matters: that's why the index of refraction in air is higher: fewer atoms to hit, so each photon travels further without hitting anything.

More on this at the bottom of THIS page.

 

[bino]

isn't c^2 faster than c. how can you have that if nothing is faster than c?

 

[pervect]

isn't c^2 faster than c. how can you have that if nothing is faster than c?

c^2 isn't a velocity. Have you been taught the concept of units yet? I don't know anything about your background. Comparing c^2 to c is a little bit like asking "what's longer, a yard, or a square yard".

 

[bino]

wouldn't c be the speed of the ship? assuming it could reach c.

 

[pervect]

From the article:

More on refraction: The high school explanation really gets on my nerves because it gives people the wrong idea about light - and the belief that C isn't constant interferes with later learning.

I've usually taken the position that 'c' is what's actually constant, the speed of transmission of energy through a media, which is what "speed of light" means if you take it literally, is not.

 

[bino]

ok are you saying that c is not constant?

 

[employee #416]

No, he means the rate at which light is absorbed and emitted is not constant. I think.

 

[bino]

oh ok that make sence.

 

[employee #416]

Yeah, I think the reason why emission and absorption is not constant is that light is absorbed through different densities. If it is absorbed in a material that has a low density, it will be absorbed less, but pass it through a dense material, and it will be absorbed fast. Emission of the photons occurs as a result of absorption.

 

[bino]

according to http://www.fourmilab.to/cship/lorentz.html the length of the ship and the lattice only appears to be contracted. it is not actually smaller it just looks like it is smaller.

 

[bino]

why is light sucked into black holes?

 

[employee #416]

bino, honestly, I agree with you about the appearance to be contracted. It's all just a way of saying our eyes are unable to measure things that move at relativistic speeds, but opinionated comments are, unfortunately, not allowed on this forum.

Light does not get "sucked" into black holes, rather it falls into black holes. The gravitational pull of a black hole is large due to it's seemingly infinite density. This pull creates an escape velocity that is larger than the speed of light. Inevitably, light is unable to escape.

 

[Nenad]

Light does not get "sucked" into black holes, rather it falls into black holes. The gravitational pull of a black hole is large due to it's seemingly infinite density. This pull creates an escape velocity that is larger than the speed of light. Inevitably, light is unable to escape.

that is once youre in the event horizon. Light can be deflected or bent from a black hole towards another object. The reason for this is that light has a mass, but it has no rest mass. So gravity has an effect on light particles.

 

[employee #416]

Yes, that light is also shifted. Gravitational-red shift takes place.

 

[bino]

so in other words c can't outrun a black hole. or is it that it is just absorbed by the hole atoms?

 

[Nenad]

according to http://www.fourmilab.to/cship/lorentz.html the length of the ship and the lattice only appears to be contracted. it is not actually smaller it just looks like it is smaller.

yes it will look smaller to the observer. The person in the spaceship will measure the spaceship to be normal length. But the reason space contracts is because the observer sees the space as moving by him at high speed and contracting. Making distance differen at different speeds.

 

[Nenad]

so in other words c can't outrun a black hole. or is it that it is just absorbed by the hole atoms?

look up black holes on the search, it will give you threads talking and explaining black holes. Its a lot easier than me answering all of your questions.

 

[bino]

so if the ship looks like it is getting smaller as it gets closer to c would the ship then dissapper if it hits c?

 

[quantumdude]

I've usually taken the position that 'c' is what's actually constant[/color], the speed of transmission of energy through a media, which is what "speed of light" means if you take it literally, is not.

ok are you saying that c is not constant?

See the part in blue[/color]. He just said that it is constant.

Yeah, I think the reason why emission and absorption is not constant is that light is absorbed through different densities.

The average speed of light is different in different media because they have different indices of refraction.

If it is absorbed in a material that has a low density, it will be absorbed less, but pass it through a dense material, and it will be absorbed fast. Emission of the photons occurs as a result of absorption.

It has to do not only with the number of absorbers per unit area, but also the length of time that each atom holds the photon.

according to http://www.fourmilab.to/cship/lorentz.html the length of the ship and the lattice only appears to be contracted. it is not actually smaller it just looks like it is smaller.

No, if an observer who is watching the ship zoom by measures the length of the ship, he will really measure it to be less than the proper length of the ship (the length in the ship's rest frame). Conversely, the people on the ship will really measure the rods of the lattice to be shorter than their proper length. It's not an optical illusion.

why is light sucked into black holes?

The photons are just following the geodesic, as they always do. In the case of black holes, the geodesic leads irrevocably to the center of attraction, with no path of escape.

 

[quantumdude]

bino, honestly, I agree with you about the appearance to be contracted. It's all just a way of saying our eyes are unable to measure things that move at relativistic speeds, but opinionated comments are, unfortunately, not allowed on this forum.

It's not just opinionated, it's also wrong.

 

[Nenad]

theoretically yes. You saw the graph. And just to add, the ship cannot ever reach c, anything with mass cannot move at c. It can go 0.9999999999999...c, but never 1c. At 1c, there is an assymptote.