How observation of a distant galaxy changes when travelling towards it

[ghwellsjr]

A good way to think about this is if you are traveling toward something at a very high speed, not only do you watch its past history unfold before your eyes, you also watch its future unfold by the same amount.

Dear Ghwellsjr,

I understand the first half of your explanation, (the past history part) since if I am at rest, and the light i receive from the galaxy should be "sent" by it in (say) 10000 years ago.
Am I right?

Yes.

but i don't get the "future unfold" part, as I move toward it, it is like i unfold its history, and at the same time the galaxy itself is still evolving .so the evolution image I observed should be twice faster as I am at rest?

is this correct?

You would see at least twice as much time go by but you will see it progressing at much faster than just twice your own rate, it could be hundreds of times faster, depending on your speed relative to the Earth and the galaxy

thank you for your help!

You're welcome.

 

[ghwellsjr]

hi all, quite a discuss, may I ask a question here...about time dilatation.

I am just thinking, we all know (approximately) how long one second is, according to our day to day life, and ( please correct me if I am wrong, sorry :) ) if something moves at v=c, for itself, time won't move at all, right?

Nothing that can measure time can move at v=c so there is never a case that time comes to a standstill.

if we travel at a speed v near c, our watch will slow down lot, so why can't I "observe" the time dilatation?

Your watch slows down a lot according to the frame in which you are traveling at almost c. In other frames, it may slow down but a lot less. And in the frame in which you are at rest, it doesn't slow down at all. But whatever frame you use to attribute time dilation to your watch will also attribute the exact same time dilation to your body so you won't notice anything different.

I mean i just assume myself as a photon traveling in vacuum at c, it should be the outside observer to say "1000 lightyears or ..." for the photon itself the time should be stopped?

As I said before, nothing that can measure time can move at c so the concept of time has lost all meaning at the speed of a photon.

once again, I am just interesting in these area, please don't laugh and help me to clarify :)

 

[ghwellsjr]

The problem is that in the case of the train, you can actually see something that correlates to the claim that is being made, namely, you can see the trees coming toward you at a slower rate.

But in the case of time dilation, there is nothing that you can see that correlates to time dilation. When you are traveling at a high speed towards a distant clock, you see the clock ticking faster than yours, not slower, and time dilation means that a clock is ticking slower than the coordinate time, not faster. In Special Relativity, with inertial reference frames, moving clocks always tick slower than the coordinate time, never faster.

As an example, if you are stationary in a frame of reference and a clock is traveling at 60% of the speed of light, it will be ticking at 80% of the coordinate time (the same as your own clock). Then if that clock is traveling toward you, you will see it ticking at double the rate of your clock and if it is traveling away from you, you will see it ticking a one-half the rate of your clock.

What are you saying that you can see that looks like time dilation?

i feel like you're just confusing things. i mean, when i look out the window and see trees flying past me, i can deduce that i am moving forward, and i can look at the window and say, look, i am moving forward, even though the trees are moving in the opposite direction. this is because by my moving forward, the trees move in the opposite direction as compared to me.

in the case of time dilatation, if i see the clock speeding up, then i can say, look, i see time dilation, even though, time dilatation is my frame of reference slowing in comparison to other frames of reference. watching the clock speed up, to me, is seeing time dilatation, it is seeing the direct effect of it, just like looking out the window seeing the trees go by in the opposite direction, is looking out the window and seeing that my train is moving forwards.

yes, of course, it must be slower. there is motion and there is still. there is no opposite of motion. entropy must increase. you cannot put energy into yourself to move slower than another object. if you reference another 3rd object, or coordinate system, then yes. but 2 objects relative to each other, may be still or may move at ever increasing speeds in comparison to each other. for which time dilatation is a result.

but, if i look out a window and i have a telescope typed thing device, that compensates for all my motion save the dilatation effect, and i view a distant planet, and i accelerate to relativistic speed, i will see the time of the planet increase, as a direct result of my time in my coordinate system slowing. so, to me, that is seeing time dilatation.

OK, now I understand what you are thinking. You are thinking that when you look out of the train and see trees approaching you, that means from your point of view the opposite is happening: you are going toward the trees.

And by the same token, you are thinking that when you approach a clock, you will see its time going faster and therefore the opposite will be happening to you: your clock will be going slower because its time is dilated.

But this is wrong. Look at these statements of yours:

time dilatation is my frame of reference slowing in comparison to other frames of reference

a direct result of my time in my coordinate system slowing

In your frame of reference, you and your clock are stationary and are not time dilated. The other clock that you are approaching is the one that is moving in your frame of reference and it is the one that is time dilated.

Note also that it is not frames of reference for which time is slowing--it is clocks moving in a frame of reference that are time dilated. All clocks are in all frames of reference. It is incorrect to say or to think of you and your clock being exclusively in your frame of reference and the other clock being exclusively in its frame of reference. You're both in each others frame of reference.

In your frame of reference, the other clock is time dilated. In the other clocks frame of reference, you and your clock are time dilated. This is why I keep saying, you can't see or measure or have any awareness of time dilation, it changes with each different frame of reference but what you can see measure and be aware of do not change with different frames of reference.

i think the op in his question, was not thinking time dilation, and was not thinking doppler effect.

he was thinking more simplistically.

i get the feeling though that in your response, you were thinking the same sort of way actually, and didn't take time dilation into effect. it seems to me at any rate.

You're right, I didn't take time dilation into effect because the op's question was not about that and even if he wasn't thinking about Doppler, that provided the answer to his question.

if the closer you get to the speed of light, the faster everything else develops around you.

how far into the future you get to when you reach the other planet, must necessarily depend on exactly how close to the speed of light you got.

i'm not certain exactly of the formula you would use to calculate the time dilatation in comparison to your speed relative to the speed of light, and although, as v→c i would expect time to tend to zero, i.e. you do not age, i would expect that this would have a non converging effect on the speed at which other things occur around you.

iow, i would expect that as time dilates for you, it increases for others, and while the formula would dictate for you a converging number, 0, as your speed approaches c, i would expect that opposite would occur for time of other frames of reference, meaning they would be divergent, which would therefore indicate that the actual precise speed at which you travel would be important in defining what it is you would see happen to the galaxy as you approach it, and to stipulate moving at the speed of light, which is impossible, you would need to conclude that the universe would be over, since all things around you aged at an infinite rate, given you aged at a rate of 0.

otherwise, there is a maximum rate at which time can pass for a reference frame, and that would be the speed at which it may pass as you go at the speed of c. and this would imply that there is a slowest possible speed as compared to you, whereas this would not sit nicely with relativity, and lack of any reference other than c.

Everything sits nicely with relativity. If it doesn't appear that way to you, it's because you don't understand relativity. In the above quote, you are mixed up with regard to time dilation and Relativistic Doppler. There is no upper limit on the Doppler factor as you are approaching other objects or clocks. But this has nothing to do with how much the other object ages. The amount that it ages is opposite to the speed at which you approach it. As I said in post #5, if you approach it at almost c, it will age by double the number of light years away when you started. If you approach it more slowly, it will age more. You've got it backwards.

now, some of what i said might be wrong. it is speculation. i don't know the math.

Why don't you learn the math? It's very simple. I went through the math for Doppler in post #20. Didn't you think that was simple?

but the original question i think is missing key information. i think it matters exactly at what speed you go. and that can't be c. i would expect that the formula for time dilation might yield even a exponential increase in time dilation as you approach the speed of light, meaning every tiny fraction of the speed light that you increase upon, makes the world around you seem to accelerate much faster, as your time frame slows in comparison to theirs.

so, i think this question must be answered using the formula for time dilation.

No, you don't have to use the formula for time dilation, the formula for Relativistic Doppler is all you need to answer the OP's question.

after a quick check on wikipedia, this seems to at least not be in disagreement with what i was saying.

http://en.wikipedia.org/wiki/Time_dilation#Time_dilation_due_to_relative_velocity

I have already pointed out problems with your understanding and application of time dilation.

 

[UglyNakedGuy]

Nothing that can measure time can move at v=c so there is never a case that time comes to a standstill.

Your watch slows down a lot according to the frame in which you are traveling at almost c. In other frames, it may slow down but a lot less. And in the frame in which you are at rest, it doesn't slow down at all. But whatever frame you use to attribute time dilation to your watch will also attribute the exact same time dilation to your body so you won't notice anything different.

As I said before, nothing that can measure time can move at c so the concept of time has lost all meaning at the speed of a photon.

I want to say thank you first, before i got any further questions...I need some time to digest these :)