Relativity theory of Einstein: a remark

Astronomy, Chemistry, Earth Sciences, Mathematics & Physics.

Moderators: Calilasseia, ADParker

Relativity theory of Einstein: a remark

#1  Postby Newstein » Aug 04, 2016 8:44 pm

Does somebody know how Einstein took the slowing down of observation into account?
Did he put it into his formulas? Observation is light and light is slow too at great distances.
Newstein
THREAD STARTER
 
Posts: 721

Country: Belgium
Belgium (be)
Print view this post

Ads by Google


Re: Relativity theory of Einstein: a remark

#2  Postby Thommo » Aug 04, 2016 10:31 pm

I don't honestly understand your question.

Einstein had two theories, the special theory of relativity and the general theory of relativity. The special theory amounts to the postulate (subsequently experimentally confirmed) that the observed speed of light is the same in different inertial frames of reference and a lot of rather clever corollaries of that proposition.

The general theory amounts to (in exceptionally reductionist terms) the idea that space tells mass how to curve and mass tell space how to curve. That the "straight lines" of Galilean relativity are actually geodesics in a much more complicated space. The corollaries of that are even more clever and even more complex.

I have absolutely no idea how that would relate to a "slowing down of observation" or what that even means, sorry.
User avatar
Thommo
 
Posts: 27175

Print view this post

Re: Relativity theory of Einstein: a remark

#3  Postby Newstein » Aug 04, 2016 11:13 pm

When a object passes at high speed, he said the time is different for both viewers.
But when you look at a moving object far away, it takes some time to see the object because the light has to reach you.
If it passes right in front of you (closest), you will get no extra delay of observation (except the time needed to reach your eyes) but when it is further away from you, the extra time or observation delay will be there because of Pythagoras...
Newstein
THREAD STARTER
 
Posts: 721

Country: Belgium
Belgium (be)
Print view this post

Re: Relativity theory of Einstein: a remark

#4  Postby Evolving » Aug 05, 2016 6:59 am

Like Thommo, I'm struggling a little to understand your question. Maybe this will help; apologies if it doesn’t in fact address your question.

An example of something travelling at a very high speed that we observe at a great distance might be a star surrounded by a halo of matter ejected in an earlier event, which then goes supernova. The first thing we observe will be the flash from the supernova itself; then, after a little while, the light will reach the halo, and for a short period of time we can observe an illuminated ring surrounding the star. The delay between the initial flash and the brightening of the halo represents the time taken for the light to travel, and because we know how fast light travels, we can calculate how far away the supernova is by measuring that delay.

Of course we know that we’re not observing these events in real time: if the supernova is, say, 100,000 light years away, then these events actually occurred 100,000 years ago; but that doesn’t matter for our purposes, because the only thing that matters is the time that elapses between the initial flash and the appearance of the illuminated ring.

That only works, strictly, if the travel that we are observing is at right angles to our line of sight. We have to be very careful where that is not the case. For instance (and this is an example brought up a few months ago by another poster), consider a jet of matter that has been ejected by an active galactic nucleus, is travelling at close to the speed of light at a small angle to our line of sight (it will just miss us if it carries on unabated), and is emitting light as it goes. If we observe the light that arrives on Earth at two different points in time, A and B, and estimate the distance across the sky between the two places at which the light was emitted (assuming we know from other methods how far away the jet is from us), we can get wildly inaccurate results for the jet’s transverse motion if we don’t make an adjustment for the radial motion. We have to take into account that the light that we observe at A was emitted much further away than the light we observe at B, and it has therefore taken longer to travel the transverse distance across the sky than the delay between times A and B.
How extremely stupid not to have thought of that - T.H. Huxley
User avatar
Evolving
 
Name: Serafina Pekkala
Posts: 11993
Female

Country: Luxembourg
Luxembourg (lu)
Print view this post

Re: Relativity theory of Einstein: a remark

#5  Postby Evolving » Aug 05, 2016 8:48 am

Evolving wrote:The delay between the initial flash and the brightening of the halo represents the time taken for the light to travel, and because we know how fast light travels, we can calculate how far away the supernova is by measuring that delay.


Or maybe we calculate the width of the halo, if we already know the distance to the star. I'm vaguely remembering one of my astrophysics textbooks and can't quite remember which of the two it was!
How extremely stupid not to have thought of that - T.H. Huxley
User avatar
Evolving
 
Name: Serafina Pekkala
Posts: 11993
Female

Country: Luxembourg
Luxembourg (lu)
Print view this post

Re: Relativity theory of Einstein: a remark

#6  Postby Bernoulli » Aug 05, 2016 8:50 am

Newstein wrote:When a object passes at high speed, he said the time is different for both viewers.


I too don't really understand what you are asking in your OP. Regarding the bit I've quoted above, I'm assuming you are referring to observers in different frames of reference. This is the principle of simultaneity that Einstein included in his Theory of Special Relativity. I can't remember the exact details, but this is often explained with the example of a train. If two events occur on the train, an observer on the train and an observer outside the train watching the train go by can report conflicting observations about the order in which the two events occurred.
User avatar
Bernoulli
Banned Sockpuppet
 
Posts: 901

Print view this post

Re: Relativity theory of Einstein: a remark

#7  Postby Pulsar » Aug 05, 2016 9:15 am

Newstein wrote:When a object passes at high speed, he said the time is different for both viewers.
But when you look at a moving object far away, it takes some time to see the object because the light has to reach you.
If it passes right in front of you (closest), you will get no extra delay of observation (except the time needed to reach your eyes) but when it is further away from you, the extra time or observation delay will be there because of Pythagoras...

If you have two objects, both moving at the same velocity with respect to you, but one nearby and one faraway, then obviously the light of the nearby object will reach you sooner than the light of the distant object. But the time dilation you observe will be the same for both objects: a clock attached to the nearby object will appear to slow down just as much as a clock attached to the distant object. Time dilation depends on relative velocity, not on distance.
"The longer I live the more I see that I am never wrong about anything, and that all the pains that I have so humbly taken to verify my notions have only wasted my time." - George Bernard Shaw
User avatar
Pulsar
 
Posts: 4618
Age: 43
Male

Country: Belgium
Belgium (be)
Print view this post

Ads by Google


Re: Relativity theory of Einstein: a remark

#8  Postby Alan B » Aug 05, 2016 9:21 am

Newstein wrote:Observation is light and light is slow too at great distances.


Is it? :scratch:
I have NO BELIEF in the existence of a God or gods. I do not have to offer evidence nor do I have to determine absence of evidence because I do not ASSERT that a God does or does not or gods do or do not exist.
User avatar
Alan B
 
Posts: 9999
Age: 84
Male

Country: UK (Birmingham)
United Kingdom (uk)
Print view this post

Re: Relativity theory of Einstein: a remark

#9  Postby Newstein » Aug 05, 2016 9:41 am

Alan B wrote:
Newstein wrote:Observation is light and light is slow too at great distances.


Is it? :scratch:


Compare it with sound delay. When a plane passes, sound is behind. At great distances, it's the same with light = observation.
That's what I try to explain.
Newstein
THREAD STARTER
 
Posts: 721

Country: Belgium
Belgium (be)
Print view this post

Re: Relativity theory of Einstein: a remark

#10  Postby Evolving » Aug 05, 2016 9:57 am

Sound doesn't travel at a constant speed. Light does (in a vacuum), for every observer; that is the whole point of special relativity.
How extremely stupid not to have thought of that - T.H. Huxley
User avatar
Evolving
 
Name: Serafina Pekkala
Posts: 11993
Female

Country: Luxembourg
Luxembourg (lu)
Print view this post

Re: Relativity theory of Einstein: a remark

#11  Postby Newstein » Aug 05, 2016 10:46 am

Evolving wrote:Sound doesn't travel at a constant speed. Light does (in a vacuum), for every observer; that is the whole point of special relativity.


That has nothing to do about it.

If an object is stationary at 1 lightsecond away from you, you will see it after 1 second.
If an object if moving at lightspeed to the right, the object will be 1 lightsecond away from that point in 1 second.
The observer will see the moving object in that point in exactly 1,41421 seconds. (square(2)) That's a delay of 0.41421.. seconds
Newstein
THREAD STARTER
 
Posts: 721

Country: Belgium
Belgium (be)
Print view this post

Re: Relativity theory of Einstein: a remark

#12  Postby Alan B » Aug 05, 2016 10:55 am

Newstein wrote:
Alan B wrote:
Newstein wrote:Observation is light and light is slow too at great distances.


Is it? :scratch:


Compare it with sound delay. When a plane passes, sound is behind. At great distances, it's the same with light = observation.
That's what I try to explain.


I see. So if a body (of infinite mass) emitting light travels past the observer at light speed, the observer will see the light after the body has passed the observer...

hmmm! :think:

Or maybe the observer won't 'see the light'...
I have NO BELIEF in the existence of a God or gods. I do not have to offer evidence nor do I have to determine absence of evidence because I do not ASSERT that a God does or does not or gods do or do not exist.
User avatar
Alan B
 
Posts: 9999
Age: 84
Male

Country: UK (Birmingham)
United Kingdom (uk)
Print view this post

Re: Relativity theory of Einstein: a remark

#13  Postby Pulsar » Aug 05, 2016 10:57 am

You're confusing time delay with time dilation. Time delay means that you see one event x seconds after another event. Time dilation means that you see an event in slow motion.
"The longer I live the more I see that I am never wrong about anything, and that all the pains that I have so humbly taken to verify my notions have only wasted my time." - George Bernard Shaw
User avatar
Pulsar
 
Posts: 4618
Age: 43
Male

Country: Belgium
Belgium (be)
Print view this post

Re: Relativity theory of Einstein: a remark

#14  Postby Evolving » Aug 05, 2016 11:10 am

Newstein wrote:
Evolving wrote:Sound doesn't travel at a constant speed. Light does (in a vacuum), for every observer; that is the whole point of special relativity.


That has nothing to do about it.

If an object is stationary at 1 lightsecond away from you, you will see it after 1 second.
If an object if moving at lightspeed to the right, the object will be 1 lightsecond away from that point in 1 second.
The observer will see the moving object in that point in exactly 1,41421 seconds. (square(2)) That's a delay of 0.41421.. seconds


I think I'm beginning to see what you're getting at, and my response is basically what I said in my first reply to you: yes, in practice we have to take into account the different distances (from the observer) at which light is emitted at different times; if we don't do that, we get utterly wrong results.
How extremely stupid not to have thought of that - T.H. Huxley
User avatar
Evolving
 
Name: Serafina Pekkala
Posts: 11993
Female

Country: Luxembourg
Luxembourg (lu)
Print view this post

Re: Relativity theory of Einstein: a remark

#15  Postby Alan B » Aug 05, 2016 11:15 am

Nah. I'm just paraphrasing his 'sound' analogy.
I have NO BELIEF in the existence of a God or gods. I do not have to offer evidence nor do I have to determine absence of evidence because I do not ASSERT that a God does or does not or gods do or do not exist.
User avatar
Alan B
 
Posts: 9999
Age: 84
Male

Country: UK (Birmingham)
United Kingdom (uk)
Print view this post

Ads by Google


Re: Relativity theory of Einstein: a remark

#16  Postby Newstein » Aug 05, 2016 11:47 am

Evolving wrote:
Newstein wrote:
Evolving wrote:Sound doesn't travel at a constant speed. Light does (in a vacuum), for every observer; that is the whole point of special relativity.


That has nothing to do about it.

If an object is stationary at 1 lightsecond away from you, you will see it after 1 second.
If an object if moving at lightspeed to the right, the object will be 1 lightsecond away from that point in 1 second.
The observer will see the moving object in that point in exactly 1,41421 seconds. (square(2)) That's a delay of 0.41421.. seconds


I think I'm beginning to see what you're getting at, and my response is basically what I said in my first reply to you: yes, in practice we have to take into account the different distances (from the observer) at which light is emitted at different times; if we don't do that, we get utterly wrong results.


But did Einstein took this into account? In what formula?
I think he just messes up with the time, which will basically have the same result I guess.
Newstein
THREAD STARTER
 
Posts: 721

Country: Belgium
Belgium (be)
Print view this post

Re: Relativity theory of Einstein: a remark

#17  Postby Bernoulli » Aug 05, 2016 11:56 am

Newstein wrote:
Evolving wrote:Sound doesn't travel at a constant speed. Light does (in a vacuum), for every observer; that is the whole point of special relativity.


That has nothing to do about it.

If an object is stationary at 1 lightsecond away from you, you will see it after 1 second.
If an object if moving at lightspeed to the right, the object will be 1 lightsecond away from that point in 1 second.
The observer will see the moving object in that point in exactly 1,41421 seconds. (square(2)) That's a delay of 0.41421.. seconds


I still don't get what you are trying to say. That object will take 1 second to get to a point 1 lightsecond away, and then the light from the object at that point will take another second to get to the observer. Where are you getting square root of 2 from?
Last edited by Bernoulli on Aug 05, 2016 11:59 am, edited 1 time in total.
User avatar
Bernoulli
Banned Sockpuppet
 
Posts: 901

Print view this post

Re: Relativity theory of Einstein: a remark

#18  Postby Evolving » Aug 05, 2016 11:58 am

(EDIT: This is in response to Newstein, not Bernoulli.)


No, that's a misconception. You're talking about time delay; Einstein is all about time dilation; and as Pulsar pointed out, those are two completely different things.

It's straightforward to observe time dilation where the time delay between the beginning and the end of the observation is negligible: for instance with muons created in the Earth's atmosphere by cosmic rays; there, the experimental results are as predicted by Einstein. Where time differences are significant, as with the relativistic jets that I was talking about, we have to make that adjustment, and then, again, the results conform with Einstein's theoretical prediction.

We don't make the adjustment in Einstein's formula; we make it first, and then apply Einstein's formula.
Last edited by Evolving on Aug 05, 2016 12:03 pm, edited 1 time in total.
How extremely stupid not to have thought of that - T.H. Huxley
User avatar
Evolving
 
Name: Serafina Pekkala
Posts: 11993
Female

Country: Luxembourg
Luxembourg (lu)
Print view this post

Re: Relativity theory of Einstein: a remark

#19  Postby Bernoulli » Aug 05, 2016 12:00 pm

If he's talking about time dilation, then that is most definitely included in Einstein's calculations.
User avatar
Bernoulli
Banned Sockpuppet
 
Posts: 901

Print view this post

Re: Relativity theory of Einstein: a remark

#20  Postby Evolving » Aug 05, 2016 12:00 pm

Bernoulli wrote:
Newstein wrote:
Evolving wrote:Sound doesn't travel at a constant speed. Light does (in a vacuum), for every observer; that is the whole point of special relativity.


That has nothing to do about it.

If an object is stationary at 1 lightsecond away from you, you will see it after 1 second.
If an object if moving at lightspeed to the right, the object will be 1 lightsecond away from that point in 1 second.
The observer will see the moving object in that point in exactly 1,41421 seconds. (square(2)) That's a delay of 0.41421.. seconds


I still don't get what you are trying to say. That object will take 1 second to get to a point 1 lightsecond away, and then the light from that object at that point will take another second to get to the observer. Where are you getting square root of 2 from?


A right-angled triangle. One side of it is the distance to the object at the start, the second side is the distance travelled by the object, and the third side is the hypotenuse and is the distance to the object at the end of the observation. That's what Newstein meant when he mentioned Pythagoras in the OP.
How extremely stupid not to have thought of that - T.H. Huxley
User avatar
Evolving
 
Name: Serafina Pekkala
Posts: 11993
Female

Country: Luxembourg
Luxembourg (lu)
Print view this post

Next

Return to Physical Sciences & Mathematics

Who is online

Users viewing this topic: No registered users and 1 guest