Speed of light and delays

[Modelexis]

Beyond doesn't have a science subforum so I'll try here.

1. a plane takes off from earth and travels the distance equal to that of the sun (approx 8 minute delay in light travel)

2. the plane has blinking lights that blink at a constant rate that never changes.

3. you watch from the surface of the earth and use a telescope that can follow the plane all the way to the sun.

Q: while you are observing the blinks, what will you notice?

Will they,

a) appear to remain the same as when the plane took off from earth

b) take longer between each blink at a gradual rate

c) appear to blink closer together

d) overlapping blink patterns

e) other?

This might sound like a stupid question to some people, especially on beyond, but I didn't go to university or anything post secondary so I still have a lot of questions about physics/science.

My primitive hominid brain cannot figure this one out.

[rufi0]

my guess would be something that looked like a dashed line representing the blinks

[Modelexis]

If the gap was 1 second between blinks, at 1 second delay you would have 2 seconds, then blink, and then the second blink would blink when you saw the first and then take another second to come into view.

then for 2 second delay, it would blink, then take two seconds to reach you, while that is happening, the second blink would happen one second before the first reached you, and then that would reach you 2 seconds later, but only 1 second away from the first.

So this leads me to think that they would stay the same distance apart, but this cannot be possible!

The distance between blinks would exponentially grow?

Can anyone find where I have gone wrong in this diagram?



I think I fixed my error



So it stays the same with the exception of the first blink?

I'm so confused

[rufi0]

lol i can tell this is going to bug you for the rest of the night

actually, from the perspective of the plane, everything else (if you looked outside the plane) would be slowing down / not moving at all, but the person inside would still see the blinking light going on/off every second as if normal. so i guess the observer on earth would probably just see streaks or patterns of moving light

[Modelexis]

This is def preventing me from going to sleep right now.

I fully grasp that the person in the plane would never notice a change, but from the observer on earth I still can't figure out what it would look like.

[hampstor]

I think what'll happen is:

- The rate will stay the same. The only difference is the 'blink' an observer will see here on earth when the plane reaches the sun will be at t+8 seconds after the plane projected the light. It won't matter how fast the plane is accelerating or if it's coasting.
- Depending on how fast the plane is going, the light will become redshifted. If the plane accelerates constantly it will become more redshifted (Doppler effect)

Of course... someone who actually has a physics degree should answer this. I'm just taking a guess

Oh and yes, the plane will take off.

[Abeo]

think of it like the Doppler effect... it may help you grasp it

think of a motorcycle, say a Harley, because they thump rhythmically, not unlike your light flashing. As it comes towards you, it sounds higher pitched (sound pulses are "stacking up") and as it goes past, it sounds lower (larger gap between pulses, the time between pulses plus the time it travels between pulses)

I would think if the plane was fast enough, you would notice the flashing rate would be slower than the plane sitting still

[Abeo]

Next question: If you have a plane and a giant treadmill.....

[hampstor]

Originally posted by Abeo
think of it like the Doppler effect... it may help you grasp it

think of a motorcycle, say a Harley, because they thump rhythmically, not unlike your light flashing. As it comes towards you, it sounds higher pitched (sound pulses are "stacking up&quot and as it goes past, it sounds lower (larger gap between pulses, the time between pulses plus the time it travels between pulses)

I would think if the plane was fast enough, you would notice the flashing rate would be slower than the plane sitting still

iirc doppler effect changes the frequency, not the rate of a wave. The sound of the motorcycle changes pitch as it approaches/moves away from you, but the individual 'blub blub blub' rate of the exhaust does not change so long as the driver does not apply/back off on the throttle.

[Abeo]

Originally posted by hampstor


iirc doppler effect changes the frequency, not the rate of a wave. The sound of the motorcycle changes pitch as it approaches/moves away from you, but the individual 'blub blub blub' rate of the exhaust does not change so long as the driver does not apply/back off on the throttle.

I agree with you... but could you explain what you mean by 'rate of the wave'?

I think we are using different terms to describe the same thing

[mazdavirgin]

Originally posted by Modelexis
Beyond doesn't have a science subforum so I'll try here.

1. a plane takes off from earth and travels the distance equal to that of the sun (approx 8 second delay in light travel)

2. the plane has blinking lights that blink at a constant rate that never changes.

3. you watch from the surface of the earth and use a telescope that can follow the plane all the way to the sun.

Q: while you are observing the blinks, what will you notice?

Will they,

a) appear to remain the same as when the plane took off from earth

b) take longer between each blink at a gradual rate

c) appear to blink closer together

d) overlapping blink patterns

e) other?

This might sound like a stupid question to some people, especially on beyond, but I didn't go to university or anything post secondary so I still have a lot of questions about physics/science.

My primitive hominid brain cannot figure this one out.

1). Light takes ~8 minutes to reach the earth once it is emitted from the sun.

As for the rest the distances we are talking about are inconsequential when dealing with light. Red shift will not be noticeable on such a small scale. Anyways the answer to the question is it will look exactly the same way as it did on earth when the plane took off other than the fact you will be seeing the blink that occurred 8 minutes ago. The frequency will remain the same. Cosmological effects are negligible on such a "small" scale.

PS: Hampstor is right it shifts the frequency of the wave aka making light "redder". Light is shifted towards the red end of the spectrum.

[hampstor]

Originally posted by Abeo


I agree with you... but could you explain what you mean by 'rate of the wave'?

I think we are using different terms to describe the same thing

err my terminology is probably bad/wrong. I haven't taken a physics class in over 12 years.

Here's what was going thru my head: I was trying to imagine it like a sine wave. As an object approaches, the wave compresses (blue shifting), as an object moves away the wave expands (red shifting). The rate would be the pattern of whatever it is (the light on the plane, the thrum of the motor).

[rufi0]

ah doppler shift, i forgot about objects moving towards/away an observer which makes sense if it was launched and observed from earth. i was thinking observing horizontal movement durrrr

[Abeo]

Originally posted by hampstor


err my terminology is probably bad/wrong. I haven't taken a physics class in over 12 years.

Here's what was going thru my head: I was trying to imagine it like a sine wave. As an object approaches, the wave compresses (blue shifting), as an object moves away the wave expands (red shifting). The rate would be the pattern of whatever it is (the light on the plane, the thrum of the motor).

Makes sense...
So the Doppler effect would change the period of the wave (i.e. color), and the amplitude would stay the same. Color shift would depend on the velocity of the plane (to what extent it would change, I don't know)
Its been 11 years since I had to look at this stuff too, its fun though.

[luxor]

The answer is A, the light emitted from the blinks will be delayed like sunlight but the rate does not change so you will see it blink as if it was before the plane took off.

[maxomilll]

I think it would look slower, because as the plane travels towards the sun, it'll take longer for the light to reach earth.
but i have no idea

[CokerRat]

Originally posted by luxor
The answer is A, the light emitted from the blinks will be delayed like sunlight but the rate does not change so you will see it blink as if it was before the plane took off.

The plane emits the blinks at a constant rate, but since at t=0, the "blink light" arrives at you essentially immediately and at t=final the "blink light" takes 8 minutes to get to you, the observed gap between blinks would have to increase.

So observed from earth, you would see them coming in further and further apart.

Note that nothing in question says anything about the speed of the plane. It is irrelevant.

[alloroc]

Originally posted by luxor
The answer is A, the light emitted from the blinks will be delayed like sunlight but the rate does not change so you will see it blink as if it was before the plane took off.

[wintonyk]

Originally posted by CokerRat


The plane emits the blinks at a constant rate, but since at t=0, the "blink light" arrives at you essentially immediately and at t=final the "blink light" takes 8 minutes to get to you, the observed gap between blinks would have to increase.

So observed from earth, you would see them coming in further and further apart.

Note that nothing in question says anything about the speed of the plane. It is irrelevant.

Wouldn't the speed be relevant in that within every second past the distance increases. While small and rather insignificant the timing between blinks will increase. At single point the timing would remain consistent as the distance increases from earth, the distance increases for the light to travel.

I am totally just throwing something out there that makes sense to me. So B would be my answer.

[revelations]

- look up "red shift" and you will find answers

- also, sunlight takes 8 minutes to arrive on earth (not 8s)