I would like to know how long sunlight takes to reach Mars, being that
I already know that it takes 8.3 minutes for sunlight to reach Earth.

The average distance from the sun to Mars is  227,940,000 km.  The
speed of light is approximately 3 x 10^8 m/s which is 3 x 10^5 km/s.

227940000/3x10^5 = 759.8 s = 12.66 minutes. If you need a more
accurate answer use a more accurate measurement for the speec of light
and the distance between the two actually varies widely (~40000000 km)

That should show you how to do it though.

Here is the site I used

http://www.noblemind.com/search.exe?keyword=Mars+Distance+from+Sun&var=1

Sunlight, as far as it is concerned, takes zero time to reach Mars.
Though measured as taking something like twelve and a half minutes,
this is an entirely different thing. It?s slightly sloppy to describe
light in a time frame but many people do, partly because of the
difficulty in conveying concepts and partly because though light
itself is not within time, most experiential interactions are.

Best

Hi Scotty, Aeh and Guzzi,

It's a concept that I have tried to drum into my mind for years. As
Scotty says .. it takes over 8 minutes for the Sun's light to reach
Earth. It is said that looking at stars is looking back in time, as
the light time is of then.

Guzzi .. what is your comparison to the argument of looking back in
time, if light is indeed instant? I was also told that light is
instantaneous, it's just a matter of wavelenghts. Like the Doppler
Effect of sound waves compressed and stretched, this sort of makes
sense to me. But I can't wrap my mind around how a light beam can
arrive at differing points in distance from the same source of
propogation.

If I'm on the right track, then how can the light source know it's
target before it has reached the target/targets? OR .. is the timing
measured as a reflection from the target back to the light source, not
from the propogation? If that is so, then the varied wavelengths
almost make logic to me, but not quite. If the distance is measured by
the lenghth of the wave, then a long flat wave could indeed be the
same length as a short erratic wave. This might explain the
instantaneous arrival, but how is it measured?

Phil

all i can tell u is one thing the speed of light differs from the
matter in which it travels.actually the speedof light differs in the
universe.u may think that the speed of light is constant.since we do
not know what the universe is actually made of any measurement made
with the speed of lght can't be accurate.and therefore there must be
margin of errors.

All i can tell u is one thing the speed of light differs from the
matter in which it travels.actually the speed of light differs in the
universe.u may think that the speed of light is constant.since we do
not know what the universe is actually made of,any measurement made
with the speed of lght can't be accurate.and therefore there must be
margin of errors.

And note one point that the speed of light what is mentioned is in
vacuum but the universe is made of plasma so there may be a change in
the measurements also.

I must say,you are some smart guys.
indian_scientist-ga?
what do you meen when you say "the universe is made of plasma"

I know that ?Answers? isn?t supposed to be a discussion group but I
hope I may be excused on the basis of interest.

Hi again silver. Yea it?s a tough one. Feynman used to try to
visualise from a particle?s perspective. In this sense, a photon
doesn?t experience time, and travels instantly. It *is*
extraordinarily difficult visualising photons with all the attendant
characteristics of a wave extending in a physical dimension and time,
doppler, refractive index effects etc, whilst not itself experiencing
time. Trouble is, there are no adequate analogies.

So a photon is infinitely long too. But that?s not so daft because a
photon energy is exact, therefore the wave-function is infinitely long
-- or the other way about. The ear hears one sine cycle of sound as a
click -- in fact it takes quite a few cycles before one hears a tone.
The ear is actually doing a reasonable job of Fourier analysis and a
spectrum analyser would indicate lots of harmonics for the short
bursts. A pure sine wave is therefore of infinite duration, ie from
before the start of time till after the end of time. Apply the
reasoning to photons and you get the same thing except anything
travelling at the speed of light gets anywhere instantly and is
infinitely long. Matter would have infinite mass at the speed of light
but photons are massless though their energy can be transform to mass
and vice versa.

As for the position of a photon, which is measurable as the transition
time from A to B, one should view it as a wave function which is very
clear at the point of measurement but fades away in both directions.
The rapidity of the fading is dependent upon how precisely the point
of measurement is.

This all means that when we ?see how the universe was? by looking at
distant stars, what we see is the stars as they are at that moment.
However, our moment is not theirs, yet it is. Yes we are looking at
earlier times but we are also looking at time as it is because the
photons arrived instantly as far as they are concerned, and there
isn?t any way of going faster than light unless you bend time.

Bet this doesn?t help at all :-)

Best

Hi again people,

If we type quietly, do you think we may be allowed to continue this
fantastic topic of learning? I would argue on four points if the
question or comments were deleted. A/ All discussions so far are
relevant to answering the question, as the jury is still out on 8.3
minutes vs no time at all; B/ One may recall another request not so
long ago which was honoured in excess of 1000 posts; C/ Anyone
interested will contribute, no-one is forced to; and D/ The question
is far more tangible than the "meaning of life" questions.

Now that's out of the way, thanks for creating your question Scotty.
I'll send this separately before we get locked out, then I have some
questions for Guzzi. Even if we don't arrive at an iron-clad answer,
our understanding of things will be educated.

Phil

Scotty, Aeh, Indian, Dksheep, Guzzi,

Scotty .. not bad input for a $2 question hey? Looks like you have
opened up a Pandora's Box here. Are you coming back to the
contemplations of your question?

Aeh .. 12.66 minutes .. that's a very accurate answer. I bet that 12
and half minutes would have sufficed, as I know that you won't be
challenged by any earth bound stop watch.

Indian .. I had understood that also. Especially when we consider the
Earth's atmosphere. Is it accepted that light may in fact slow down
say through the Ozone layer as compared to a vacuum?

Dksheep .. Would you care to contribute further? The more questions,
the closer we might come to accepting an answer to Scotty's question.

Guzzi .. Now to the other mind set. Of course your explanation has
helped. :) Thanks for your energy and use of layman's terms. Everyone
else here has been of the opinion that light time is measurable. I
have been on the fence about it for years, with my limited
comprehension. If instant, then yes I understand that a photon must be
infinite (in both directions, large and small). Could we use an
analogy of a line being a series of points? If so, then a point is a
line itself. A line as in a wavelength particle line.

Should we consider that the photons do NOT in fact MOVE at all? But
rather the concatonating photons exist as a part of a constant
infinite line of light? I am beginning to think that when we measure
"speed" we automatically assume that the timed subject is moving. What
if it exists statically? Then our measurement of light might be
measured from the receiving target as we spin about the universe.

Why is it that we have both trains of thought on the subject?

Scotty .. also, see if you can get a copy of "A Brief History of
Time". It's by Stephen Hawking. Fantastic reading. I actually
comprehend the first 50 pages, but am having trouble with the rest of
the book.

All the best, Phil

Guzzi,

As you say, there are no adequate analogies to compare light time to
what we experience in daily life. Would you care to comment on the
concept of infinity to further educate us? Could we somehow apply the
infinity of numbers to help explain it? As in infinite in both
directions .. fractions forever smaller, yet never reaching zero as
each fraction is forever halved. Can this concept somehow be applied
to your acceptance of the instant "speed" or my suggested "static
existance" of light?

Phil

OK, so here's the deal, folks:

The speed of light in a vacuum is constant.  period.  There are no
ifs, ands, or buts.  It is equal to approximately 3 x 10^8
meters/second.

The speed of light differs as it passes through various materials. 
The speed of light is different as it passes through glass, water,
air, and the like.

To an object travelling the speed of light, "time" becomes relative. 
The faster an object travels, the more time becomes "expanded".  The
extreme case is when an object travels the speed of light.  Thus, to
an object traveling the speed of light, it would appear that
everything happens instantly.  Getting from point A to point B occurs
instantly.  Likewise, distances "shorten" to zero.  So, to the object,
it travels what appears to be zero (but really is finite) distance in
zero time.

However, to the outside observer (not travelling the speed of light),
it takes distance/speed of light for that object to reach its
destination.

For a light particle/wave/whatever you want it to be today that leaves
the sun, it takes 12 and some odd minutes for it to reach Mars
according to the earth-bound observer.  To the photon, it takes zero
time.

Remember, everything is relative...

Silver, I?m typing very quietly :-)

I should have course clarified my ramblings by adding that a photon is
infinitely long in its infinitely short universe.

Comments on infinity, wow. In a bout of insomnia, (considering elastic
/ inelastic collisions) I recently derived ?zero multiplied by
infinity equals anything?. Only in the light of day did it occur to me
that I already knew this in the more usual arrangement of ?anything
divided by zero equals infinity?. But is infinitely short the same as
zero? Well yes and no -- kinda academic. If one derives photon
characteristics from limiting condition you get infinitely short, but
derived from a perspective of absolutes, one arrives at zero. You
alluded to this.

All the conjectures you present are I think correct. That they are
apparently contradictory is because of our inability to get inside the
mind of a photon. You will be aware of the particle / wave debate
which raged way into the last century. The concept of duality was the
problem. Same human limitations apply to -- well anything, but
especially to quantum issues.

touf-ga is helpfully precise. One might say ?Ah but light is acted
upon by gravity.? Yes indeed, but so too is time so he?s still right.

The reason I prefer to view form the photon?s perspective (though not
exclusively) is that can furnish a (slightly) more qualitatively
objective analysis. After all, it worked for Feynman, who?s shoes I am
not fit to shine.

Best

I think I finally "got" it !

Great answers Touf and Guzzi.

So ..

To a stationary observer                A to B = 1T (unit of time)
A parallel observer at same speed       A to B = 0T
Approaching light source                A to B = T-
Receeding from light source             A to B = T+

This explains why I have been unable to make ends meet for years!

By relative Touf, I understand that means relative to the speed and
direction of light.

If light takes 12.66 minutes to reach Mars, according to the earth
bound observer .. how long would it take according to the Mars bound
observer?

Both of you, please leave your shoes at the door for shining.

Regards, Phil

<types quietly>...
silver777-ga asked "If light takes 12.66 minutes to reach Mars,
according to the earth bound observer .. how long would it take
according to the Mars bound
observer?"

It will be the same amount of time (about 12.66 minutes in this case)
for Mars-bound observer also, as planetary speeds are almost zero
compared to light speed.  This assumes "minutes" are counted same as
on earth (i.e., based on seconds related to atomic motion, rather than
on planetary motion).

You can give an approximation if you have the following additional information:

Speed of Light in a Vaccum: c (in m/s)
Distance between Mars and Earth at the time: d (in m)

We than need to work out how long it takes light to reach earth from
mars in minutes. Since time = distance/speed , time in minutes = d/60c

If you then draw a triange between earth mars and the sun, fill in the
two times you know you can use trig to find the other length.