You are here:

# Relativity/spacetravel and time

Question
This is just a small point
When the scientists say:- if you were travelling at say half the speed of  light it would take "X" number of years wrt earth for your craft to get to a particular star. Is the "X" no of  years  wrt those in the  spacecraft as well as those on earth or it is shorter for those on the craft( as the clocks slows down wrt earth and the star within the craft?) -  and if it is shorter - how much? Is the  rate of slowdown of time wrt earth on the  craft linear or exponential the faster it goes.  Its interesting that at very high speeds for those on earth it might be an impossibly long time  to reach the star, for those making the  journey it could  be acceptable.

Given:
Speed of spacecraft wrt earth: 0.5 in units of c.
Time = X years wrt earth

Calculated:
Speed of spacecraft clocks wrt earth clocks = (1 + .25)^-1/2 = 0.9 approximately
Time of arrival wrt spacecraft =0.9X years

So the answer to questions 1 & 2 are No & Yes, and to 3, 10% shorter.

For 4, note that the rate of a moving clock wrt a stationary frame of reference is

(1 + v*v/c*c)^-1/2.

Your comment at the end is correct.

Ben

Relativity

Volunteer

#### Uncle Ben

##### Expertise

I can answer questions regarding Einstein's Theory of Relativity, particularly in Special Relativity. I will not answer homework questions or mathematical problems that require special symbols.

##### Experience

I have taught physics at the college level, undergraduate and graduate, for many years including Special Relativity. I have taught at Johns Hopkins, Case-Western, and MIT. I have also served as a staff member of the Commission on College Physics, which was supported by the National Science Foundation to recommend improvements in the curriculum of college physics departments in the US. I am also the author of a textbook titled Vector Calculus, which was used at MIT in the teaching of electromagnetic theory and relativity. My research interests were mainly in solid state physics, especially the properties of metals at low temperatures. I am listed in the publication known as American Men of Science.

Publications
I have dozens of papers published in the Physical Review and in the American Journal of Physics.

Education/Credentials
I hold a Ph.D. degree in physics from the Johns Hopkins University.

Past/Present Clients
Johns Hopkins University, Case-Western Reserve University, Massachusetts Institute of Technology, Empire State College, Georgetown University, Commission on College Physics, and UNESCO.