Fuel Consumption of a Ship Traveling at Near Light Speed

[JaredJames]

So at constant velocity you don't get time dilation?

Once you are no longer accelerating time moves at the same rate whether you are on the ship or not?

 

[Nabeshin]

That's not what I said. I said that at constant velocity, the people on the ship observe those on Earth to be passing slower through time and the people on Earth observe those on the ship to be passing slower through time. Nobody sees anybody else as moving FASTER through time than as measured by their own (stationary) watch. In more SR speak, the proper time between two events is always shorter than the time between the same two events in a different frame.

One cannot discuss unambiguously "the rate of time" anyways, so your question is rather meaningless without reference to with respect to whom the rate of time is being measured. If you modify the question to say "time moves at the same rate relative to the other observer whether you are the ship or Earth observer", then the answer yes.

 

[JaredJames]

OK, so as per the wiki article, if the ship experiences a 5 year journey time and the Earth 10 years, when observed from the ship the Earth would be experiencing time slower?

Am I understanding this right or way off? (I'm not arguing, I just want to clarify. What I've said so far seems ok, aside from the who's viewing what side of things from what I can tell.)

 

[DaveC426913]

If the ship is your reference frame, time experienced by everything outside the ship (travelling less than your velocity) will appear to move very quickly. 1 year on the ship will be multiple years on Earth.

No. If you look back toward Earth, you will observe everyone moving very slowly. As long as the spaceship and Earth are each in inertial reference frames, each will see the other as slower. That's the apparent paradox.


It is only once the spaceship turns around and begins its return to Earth that it will observe Earth as moving quickly.

 

[JaredJames]

Ah, now that clears it up.

 

[DaveC426913]

In this article http://www.einsteins-theory-of-relativity-4engineers.com/twin-paradox-2.html

This graph shows what a receding observer sees. Look at the left graph, bottom half. Eartyh stays put (Y-axis/time axis), spaceship moves away to right.

A signal sent out from Earth every year is received on the spaceship every two years. i.e. the spaceship on its 4 year outward journey (2007 to 2011) only receives only 2 yearly greetings from Earth.

(Of course, after it turns around, it receives 7 greetings on its 4 year homeward journey.)

 

[wrongusername]

To both observers (as I'm pretty sure I've mentioned in my previous posts) observe time passing normally.


But, the person on the ship will experience 'less' time passing than the person on the Earth.

This is true, imo, only from the person on Earth's point of view. How much slower time is passing shouldn't be absolute.

Speculatively, what if you have another spaceship, traveling at a fraction of the relativistic speed of the first spaceship? If the first spaceship undergoes 10 years of travel and decelerates to the second spaceship's frame, and the second spaceship's captain says he's been traveling for 50 years, and the first spaceship then decelerates further to be stationary with respect to Earth, would the people on Earth perhaps measure 100 years of time to have passed?

The person on the ship may undergo 10 years of travel and return, to find the Earth has undergone 100 years.

Heck, I've just read the entire wiki article and don't see a problem. From the first line:

You don't see a problem = where's the paradox? :P

Yes, but the traveller in space is changing frames. In one frame, he is traveling at whatever fraction of the speed of light relative to Earth. In 10 years or so in his time, he would change to another frame which is stationary to the person on Earth. Now suddenly the time on Earth doesn't seem to be moving slow anymore, and he finds much more time has passed on Earth somehow. I don't know how this would affect the symmetry between the two frames, but it's the explanation I've been given to the twin paradox.

 

[wrongusername]

In this article http://www.einsteins-theory-of-relativity-4engineers.com/twin-paradox-2.html

This graph shows what a receding observer sees. Look at the left graph, bottom half. Eartyh stays put (Y-axis/time axis), spaceship moves away to right.

A signal sent out from Earth every year is received on the spaceship every two years. i.e. the spaceship on its 4 year outward journey (2007 to 2011) only receives only 2 yearly greetings from Earth.

(Of course, after it turns around, it receives 7 greetings on its 4 year homeward journey.)

Wow, thanks! It makes more sense now

But in the right half of the picture, where Pam sends signals back to earth, is Earth also suddenly seeing Pam's time going really quick (4 signals in 2 years)? If so, why?

 

[DaveC426913]

But in the right half of the picture, where Pam sends signals back to earth, is Earth also suddenly seeing Pam's time going really quick (4 signals in 2 years)? If so, why?

Because she is following very closely behind her own light.