why light takes about 8 min. to reach the earth from sun

[apurvmj]

As stated in theory of relativity, as the speed of any object inceases its relative time decreases.

Is it not applicaple to light it self. At its very own speed light's relative time should be zero and it should reach earth for that matter instantly.

your view pls

Edited June 17, 2012 by apurvmj

[Greg H.]

The reason why light takes 8 minutes to reach earth from the sun is simple; we're eight light-minutes away from the sun.

 

 

Light doesn't go anywhere instantly.

[Advaithi]

If we observe a traveller who travels at great speed, we feel that his time moves slower than ours. But the one, who is traveling, feels his time is going normal. The contradiction comes only when we compare our time with his time. Otherwise everyone feels everything is alright with their own frame. We calculate the light's speed in our own frame.

Edited June 17, 2012 by Advaithi

[md65536]

Is it not applicaple to light it self. At its very own speed light's relative time should be zero and it should reach earth for that matter instantly.

 

Yes, not applicable: Light does not "experience" proper time. There's no clock or reference frame for light, such that the timing of the trip is meaningful "from light's perspective".

 

If an object is making the same trip, approaching c relative to Earth, then the Lorentz factor diverges to infinity, the length-contracted distance to the Earth approaches 0, and the locally measured time it takes to cross that small distance approaches 0.

 

 

[space stuff]

As stated in theory of relativity, as the speed of any object inceases its relative time decreases.

Is it not applicaple to light it self. At its very own speed light's relative time should be zero and it should reach earth for that matter instantly.

your view pls

 

 

Without making it complicated, I should tell you that speed of light is 300,000 km per second.

 

 

Light from Sun should reach Earth in one second if Earth would have been 300,000 km away from Sun. But it's not. We are approx. 150 million Km away.

 

 

Now, you should calculate on your own that it takes approx. 8 mins (500 seconds), by using- time = distance / speed

[swansont]

As stated in theory of relativity, as the speed of any object inceases its relative time decreases.

Is it not applicaple to light it self. At its very own speed light's relative time should be zero and it should reach earth for that matter instantly.

your view pls

 

We measure the time in our frame. In that frame, it takes ~ 8 minutes.

 

Analysis in the photon's frame is not possible. There is no rest frame of a photon; it is not in an inertial frame. As md65536 stated, this is not meaningful.

[Dekan]

We measure the time in our frame. In that frame, it takes ~ 8 minutes.

 

Analysis in the photon's frame is not possible. There is no rest frame of a photon; it is not in an inertial frame. As md65536 stated, this is not meaningful.

 

Apurvmj's OP raises an interesting point though - why doesn''t light just travel instantaneously. Why must it go at a set speed of 300,000 kps?

 

Does this speed have some essential property, which the Universe needs in order to exist. Suppose light went at a faster speed, say 600,000 kps. Or at a very much slower speed, like 10 kps.

 

Would that make the Universe different - or even impossible?

[Aethelwulf]

Apurvmj's OP raises an interesting point though - why doesn''t light just travel instantaneously. Why must it go at a set speed of 300,000 kps?

 

Does this speed have some essential property, which the Universe needs in order to exist. Suppose light went at a faster speed, say 600,000 kps. Or at a very much slower speed, like 10 kps.

 

Would that make the Universe different - or even impossible?

 

Some authors have calculated the possibility of the speed of light varying over the years, such as Barrow, who calculated the speed of light to something like [math]10^{60}[/math] times the everyday speed of light, and put this down to the possibility of a changing density structure in the spacetime continuum.

 

The speed of light today depends on two properties of the vacuum, the permittivity and the the permeability - [math]c^{-1} = \sqrt{{\epsilon \mu}}[/math]. If you could change these, you can change the speed of light.

Edited June 17, 2012 by Aethelwulf

[apurvmj]

I know that the because of distance between sun & earth, light takes aprox. 8 min.

but its just a formula based calculation, cause we never (I guess) conducted any experiment to do that.

 

# space stuff, I don't want to make complecated but its Einstein who is responsibbl,e I was very much happy with Newton's theory.

 

#md65536, as far as I know object aproching speed of light its own length decreases not the path length.

 

My one more question is when say any object (other than photon) travelling at 50% of speed of light then time frame for that object is slower by 50% but then for fixed length doesn't that object experience an ( may be psuedo) accelaration?

Edited June 17, 2012 by apurvmj

[Dekan]

Some authors have calculated the possibility of the speed of light varying over the years, such as Barrow, who calculated the speed of light to something like [math]10^{60}[/math] times the everyday speed of light, and put this down to the possibility of a changing density structure in the spacetime continuum.

 

The speed of light today depends on two properties of the vacuum, the permittivity and the the permeability - [math]c^{-1} = \sqrt{{\epsilon \mu}}[/math]. If you could change these, you can change the speed of light.

 

Thanks Aethelwulf.

 

Do you mean, that the "vacuum" isn't just an empty gap between solid objects. Instead, the "vacuum" is made of some kind of "stuff" - and this "stuff" slows down things moving through it. Things such as light-particles, ie photons. They can't get any faster than 300,000 kps. Because they encounter "vacuum-resistance", which limits their ultimate speed. That's to say, photons have a terminal velocity imposed by vacuum-resistance.

 

Like when objects fall through the air. They reach a terminal velocity, imposed by air-resistance.

 

That sounds reasonable, I suppose. But if the vacuum is made of stuff, what happens when the Universe ages and expands? Won't the vacuum expand also, so the stuff in it gets thinner? As it thins out, it will offer less resistance to particles travelling through it, like photons.

 

That will allow photons to travel faster as the Universe ages. Or to put it another way, the speed of light will steadily increase.

 

Is there any observational evidence that this is actually happening?

[Aethelwulf]

Yes, the vacuum is made of an energy density. The community seems somewhat split on whether the universes energy density is truly constant. It may dilute over time, for instance. It's one of those questions we are ''not completely sure about''. Most theories however will entertain a constant energy density.

[md65536]

#md65536, as far as I know object aproching speed of light its own length decreases not the path length.

Yes... I didn't quite specify the frame of reference.

In Earth's frame, the object's length is contracted.

In the object's frame, its own length (or local ruler) remains "normal" and the distance to Earth (as well as the depth of Earth, etc) contracts.

 

 

[apurvmj]

While searching for derivation for E= mc² I come across this http://www.adamauton.com/warp/emc2.html

firstly it was 'thought experiment'

if this is to be believed 'm' in this equation is assumed mass of photon which supposed to be zero.

and we all know that zero cant be cancelled from either sides of equation, its not valid.

its like proving 1 = 2.

correct me if I'm wrong, coz my small head is spinning.

[John Cuthber]

The rest mass of a photon is notionally zero but it does have a mass given by E=MC^2

[swansont]

While searching for derivation for E= mc² I come across this http://www.adamauton.com/warp/emc2.html

firstly it was 'thought experiment'

if this is to be believed 'm' in this equation is assumed mass of photon which supposed to be zero.

and we all know that zero cant be cancelled from either sides of equation, its not valid.

its like proving 1 = 2.

correct me if I'm wrong, coz my small head is spinning.

 

I don't see where the mass of the photon is identified. The mass of the box is. When there is a photon in the box, the box's mass increases by E/c^2. The subtlety here is talking of systems vs individual particles; for the latter one can discuss the rest mass. For composite systems there can be internal forms of energy, and the mass of the system will change by E/c^2 if energy is added or removed. However, in keeping consistent with those definitions, the mass of the photon is zero. Assigning it a mass from E=mc^2 is a different definition, and not interchangeable with the other.

 

There are a number of discussions on this already in progress.

such as http://www.scienceforums.net/topic/66798-light-has-mass/

[apurvmj]

I concluded that this all mess started due to fact that photon has momentum but no mass at rest.

Strange fellow. Ya it should gain some weight, Mr. Photon pls have some healthy food. you are driving whole world crazy.

Edited June 19, 2012 by apurvmj