Astronomy/General Relativity

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Expert: Jesse Martinez - 5/23/2010


Question
please tell me if we travel for example in 2050 AD to Proxima centauri %26 would complete our return journey within say one year in a spacecraft. we'd be older by a year when we return but what time it will be on earth when we come back?
Please let me know what is the basis of calculating the difference %26 is it possible to communicate with earth during the entire journey? If not why?
I think Proxima Centauri is 4.5 Light years away from our Earth.

Answer

Transformation
The way to figure out time dilation factors between two objects moving at different speeds was explained to me once. Usually I would not answer relativity question but I do remember the principle involved. I do not know if you mean that the ship is traveling at 26% of the speed of light relative to Earth however. But lets say that is the case.

The formula is attached as a picture since attempts to type it out failed. So I have revised this answer to be clearer, but the math will be done on your end. In the formula, t is 1, T is the speed of time relative to 1, v is the difference in speed of the objects relative to c, the speed of light, here taken as 1. So in the case of a speed of 26% the speed of light, t would equal T divided by the square root of 1 minus 0.26 squared divided by 1. This gives us T=0.9656, Which is a factor of 96.56%, so time moves only about 3% slower at speed of 0.26c. Putting in the numbers for 99% the speed of light yields a time dilation of 37.56%. 99.9% yields 4.47%. Now we are making progress. At 99.9% the speed of light, you travel about 22.37 Earth days worth in one day elapsed on your ship. At 99.99% that becomes about 71 Earth days in one day on the ship. At that speed you could cover 4.5 light years in 23 days. I am assuming the Earth itself is not moving in relation to Proxima Centauri. only to your ship. Otherwise there is an additional factor involved.

As far as communication goes, it would be possible. The faster the relative speeds, the harder it would be to understand each other. At 99%c, your voices would seem slowed down almost three times. The biggest factor would be the distance you are apart. Halfway there, your communications would take 2.25 years to reach each other, no matter what your speed. Once there the time dilation causing the apparent slow down in the speed of speech would go away, but it would take 4.5 years to send a message and another 4.5 years to receive a reply.
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Jesse Martinez

Expertise

General and specific questions about the solar system and stellar and galactic astronomy, are what I can easily answer off the top of my head. For example, what is the largest planet in the solar system? How far away is the moon? Have there been any confirmed planets in orbit around stars other than the sun? How many stars are there? The tougher ones like explaining the big bang theory and black holes I will leave to the PhD’s. Even though I could muster an answer, I would have to research it more than I would like. I would also like to answer questions that involve Astronomy with other sciences, chemistry, biology, physics, geology and mathematics as long as they are not PhD level.

Experience

I have been into astronomy since I was 8 years old. I have kept detailed journals of my observations through small telescopes. Over the years I have participated in amateur observation projects for organizations like ALPO. My personal research has involved "discovering" the moons of Jupiter with a 4½-inch Newtonian reflector without any outside information like charts and tables. In a summer long project, I determined the existence of and plotted the orbits of the four major moons of Jupiter. From these observations, my data on orbital elements was surprisingly accurate (orbital radius and orbital period).

Education/Credentials
80 hours of college credits while studying physics and geophysics. Completed correspondence photography course while in high school. Took two semesters of electronics training at a community college. Studied computers and graduated from a technical school at the turn of the millennium, gaining A+ and Microsoft Certified Professional credentials. Hablo Español. Si quieres preguntar en Español, estoy a su servicio.

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