# Actual and observed time dialation

• neh4pres
In summary, two inertial bodies that close distance on each other will observe time dilation. When one body accelerates, it actually time dilates from its frame of origin. So, if a rocket traveling under inertia toward Earth at such a speed it can cover 100,000 light years in a year (in the rockets frame due to extreme length contraction) and the rocket could accelerate at such rate that it could come to rest with the Earth in a distance of 1 meter. Then the observer on the ship would see the Earth age >100,000 years over the distance of that meter correct.f

#### neh4pres

I'm going to state that two inertial bodies that close distance on each other will (becouse of loss of simultaneity)observe time dilation. Also i will state that when one body accelerates it will actually time dilate from its frame of origin. So with this stated, if a rocket traveling under inertia toward Earth at such a speed it can cover 100,000 light years in a year(in the rockets frame due to extreme length contraction) and the rocket could accelerate at such rate that it could come to rest with the Earth in a distance of 1 meter. Then the observer on the ship would see the Earth age >100,000 years over the distance of that meter correct. If so can anyone tell me what an observer on Earth would see if looking at the ship?

You mean besides the rocket observer flattening into a pancake?

Not much, the rocket clocks which were previously running very slow in the Earth frame would start running normally.

and the rocket could accelerate at such rate that it could come to rest with the Earth in a distance of 1 meter. Then the observer on the ship would see the Earth age >100,000 years over the distance of that meter correct.

i don't think so. if the rocket and the Earth are at the same place at the same time then not much will happen.

when the rocket was 100,000 light years away and it started to accelerate to begin its journey then it would have seen the Earth age nearly 100,000 years. that's my intuition. i haven't worked it out mathematically.

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I'm going to state that two inertial bodies that close distance on each other will (becouse of loss of simultaneity)observe time dilation. Also i will state that when one body accelerates it will actually time dilate from its frame of origin. So with this stated, if a rocket traveling under inertia toward Earth at such a speed it can cover 100,000 light years in a year(in the rockets frame due to extreme length contraction) and the rocket could accelerate at such rate that it could come to rest with the Earth in a distance of 1 meter. Then the observer on the ship would see the Earth age >100,000 years over the distance of that meter correct. If so can anyone tell me what an observer on Earth would see if looking at the ship?

Granpa is correct. The ship observer will not see extreme ageing of the Earth in the last meter or so. Here is an example with slightly smaller numbers.

The rocket is 100 light years from Earth and initially statioanry. He sees an image of the Earth as it was in the year 2000. He knows that the light took 100 years to get to him so he sets his clock to the year 2100 which he estimates is the age of the Earth. He starts traveling at 0.99c and after one year of Earth time he is intercepting photons that left Earth in the year 2002. After one year on his onboard clock he sees the Earth as it was in about the year 2014. After 100 years Earth time at 0.99c he is about one light year from Earth and he is eeing the Earth as it was in the year 2199. The actual year on Earth is 2200 at the point. So it will take just over a another year to finally arrive at Earth and nothing extreme happens in that last year. When he arrives in about the year 2001 Earth time, his clock will indicating that it is year 2014 ship time, so he will have seen the Earth age about 201 years while his clock has only advanced about 14 years. He will have seen the Earth ageing consistently fast (about 14 years for every year that passes on the ship clock) over the entire period of his journey, not just at the end.

i had the thought experiment set up so that the rocket was traveling under inertia with no acceleration to get to speed

sorry kev but that cannot be true.. if two bodies are inertially traveling toward each other they will both see the others clock as being the slow one. so the space man can not see the Earth age fast he would still see the Earth age slow until one or the other accelerates

im also going to add this. i know that over the distance traveled.. 100,000 light years, that the Earth will appear younger at a distance than it will up close because of the distance the light traveled. so let's get rid of the problem by saying the rocket observer will look at the Earth only just before he accelerates to come to rest and the whole time the rocket is accelerating to get to that rest state

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this is something i wrote in the forum "are relativistic effects real"

"think of two rockets moving at each other under inertia at a course so that they pass very close. Observer A will look at both clocks when the rockets pass. he will see his own as being T and he will see observer B,s clock as being .5T ...Observer B will see his clock as being T and he will see Observer A's clock as being .5T"

that being said.. if both rockets accelerate the same amount so as to come to rest beside each other, during the acceleration each will see the others clock run faster than his own and at the point they come to rest both clocks should read the same time.

this is something i wrote in the forum "are relativistic effects real"

"think of two rockets moving at each other under inertia at a course so that they pass very close. Observer A will look at both clocks when the rockets pass. he will see his own as being T and he will see observer B,s clock as being .5T ...Observer B will see his clock as being T and he will see Observer A's clock as being .5T"
Not true. At the instant the two ships pass each other, observers in both ships will agree as to what readings both clocks have. This is the only moment at which they will agree.

Not true. At the instant the two ships pass each other, observers in both ships will agree as to what readings both clocks have. This is the only moment at which they will agree.

if so and if up to that point they both see the other observers clock as ticking slow then at what point to they speed up so as that they can both agree as they pass each other?

if so and if up to that point they both see the other observers clock as ticking slow then at what point to they speed up so as that they can both agree as they pass each other?

At no point. They just won't agree as to when each other's clock started ticking.

For example, let's assume that at the instant they pass, both observer's agree that their respective clocks read T secs. Both observers note that the other clock is ticking at half the rate as his. What this means is that Observer A will determine that Clock B had ticked off 0.5 T secs before his own clock ever started and Observer B will determine that Clock A had ticked off 0.5 T secs before his own clock ever started