# The Naked Scientists Forum

### Author Topic: Observed Time and Special theory of Relativity questions.  (Read 2173 times)

#### user001

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##### Observed Time and Special theory of Relativity questions.
« on: 06/05/2015 04:10:39 »
I have a few questions.

1: In theory could we build a telescope so large it could see what aliens were doing on another planet?

2:  Take the hypothetical traveling twin as example from the special theory of relativity.  If someone was traveling near speed of light in a ship for 2 years and had 2 years of video, while 30 years passed on Earth. How long would the video be when they got back to earth?

2a: If there is 30 year of video and person ages 2 years, is person moving in slow motion?

3: If a ship was traveling near speed of light and had a live laser video feed hooked up to a feed on earth the whole time, what would the screen show; How would each observer see the others "time" passing?

3a. Would observing time passing on earth disrupt the relativity of time for the person on the spaceship?

3b: How much food would need to be on the ship, 2 years or 30 years worth?

#### PmbPhy

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##### Re: Observed Time and Special theory of Relativity questions.
« Reply #1 on: 06/05/2015 04:35:36 »
Quote from: user001
I have a few questions.

1: In theory could we build a telescope so large it could see what aliens were doing on another planet?
I seriously doubt it. By the time the light gets here over, say, a distance of 100 light years the intensity of the light is so low that there wouldn't be enough photons to get enough detail to resolve an individual alien.

Quote from: user001
2:  Take the hypothetical traveling twin as example from the special theory of relativity.  If someone was traveling near speed of light in a ship for 2 years and had 2 years of video, while 30 years passed on Earth. How long would the video be when they got back to earth?
I don't understand. First, by "in a ship for 2 years" I assume that you mean that during the trip only two years passed as measured by observers on the ship. Also, what you mean by "had two years of video". Do you mean that someone in the traveling twin's spaceship was taking video during those two years? If so then the video would be the same size. How could it be anything else?

Quote from: user001
2a: If there is 30 year of video and person ages 2 years, is person moving in slow motion?
Yes.

Quote from: user001
3: If a ship was traveling near speed of light and had a live laser video feed hooked up to a feed on earth the whole time, what would the screen show; How would each observer see the others "time" passing?
There are two effects in operation here. One is the fact that it takes longer and longer for the light to travel from ship to earth. This is related to the Doppler effect. When that's taken into account things "appear" to be moving slower than they really are. Then there's the fact that time "really is" slowed down on the ship so you have to take that into account as well.

Quote from: user001
3a. Would observing time passing on earth disrupt the relativity of time for the person on the spaceship?
No. Why would it?

Quote from: user001
3b: How much food would need to be on the ship, 2 years or 30 years worth?
Two years worth. Please keep in mind that time really is slowed down for observers in the ship as reckoned by observers on Earth. Also keep in mind that time really is slowed down for observers on Earth as reckoned by observers on the ship.

#### Bill S

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##### Re: Observed Time and Special theory of Relativity questions.
« Reply #2 on: 06/05/2015 13:51:27 »
Quote from: Pete
Two years worth. Please keep in mind that time really is slowed down for observers in the ship as reckoned by observers on Earth. Also keep in mind that time really is slowed down for observers on Earth as reckoned by observers on the ship.

“…time really is slowed down for observers in the ship as reckoned by observers on Earth.”  Therefore they need only two years’ worth of food.

“…time really is slowed down for observers on Earth as reckoned by observers on the ship.” But they need thirty years’ worth of food.

#### David Cooper

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##### Re: Observed Time and Special theory of Relativity questions.
« Reply #3 on: 06/05/2015 18:37:24 »
3: If a ship was traveling near speed of light and had a live laser video feed hooked up to a feed on earth the whole time, what would the screen show; How would each observer see the others "time" passing?

During the outward journey, the observers on Earth would see the action slowed down much more than the actual slowing within the ship, but during the return journey they would see the action slowed much less. On average they would see the action happening at 1/15 the normal rate.

If you are sending video from the Earth to the ship at the same time, the people on the ship will see the action on Earth happening on average at 15 times the normal rate, but it will look much slower than that during the outward journey (to the point that all the action appears to be taking place in slow motion) and it will look much faster than 15 times the speed of action on the way back. The difference in the observed speed of action in the video reaching the ship will be much greater between the outward and return legs of the journey than the much lesser difference in the observed speed of action in the video reaching the Earth between the outward and return legs.

#### user001

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##### Re: Observed Time and Special theory of Relativity questions.
« Reply #4 on: 24/09/2015 00:12:18 »
It has quite some time. but I wanted to clear so question up.

If a ship was traveling near speed of light in EARTH'S ORBIT and had a live laser video feed hooked up to a feed on earth the whole time (say near one of the poles so laser contact never broken), what would the screen show; How would each observer see the others "time" passing? If we receiving info at the speed of light and it traveling at the speed of light.?.?.?

2:Take the hypothetical traveling twin as example from the special theory of relativity.  If someone was traveling near speed of light in a space ship for 2 years and had 2 years of video, while 30 years passed on Earth. How long would the video be when they got back to earth? So when they got back to earth their 30 year journey would be on that two years of tape just slowed down?

3:3b: How much food would need to be on the ship, 2 years or 30 years worth?

Two years worth. Please keep in mind that time really is slowed down for observers in the ship as reckoned by observers on Earth. Also keep in mind that time really is slowed down for observers on Earth as reckoned by observers on the ship.

So not only would we perceive time different, our metabolisms would change? The electronically functions of the brain slow down also?

#### The Naked Scientists Forum

##### Re: Observed Time and Special theory of Relativity questions.
« Reply #4 on: 24/09/2015 00:12:18 »