Naked Science Forum
Non Life Sciences => Physics, Astronomy & Cosmology => Topic started by: yor_on on 23/09/2010 23:33:35
-
I read this but I'm not sure of how to understand it?
"Objects in free-fall really do not accelerate, but rather the closer they get to an object such as the Earth, the more the time scale becomes stretched due to spacetime distortion around the planetary object (this is gravity). An object in free-fall is in actuality inertial, but as it approaches the planetary object the time scale stretches at an accelerated rate, giving the appearance that it is accelerating towards the planetary object when, in fact, the falling body really isn't accelerating at all. This is why an accelerometer in free-fall doesn't register any acceleration; there isn't any." From Equivalence principle (http://en.wikipedia.org/wiki/Equivalence_principle#Development_of_gravitation_theory)
Yes, a free-falling object is in a 'inertial motion' if we by that mean that a object in motion will remain in motion, just as a object 'at rest' will remain 'at rest', until acted on by some external force. And that's not weird, but I lose sight of how the author thought here as he don't define from what frame he observe this 'phenomena' of 'stretched time'? And the free fall in itself explains very nicely, thank you, why an accelerometer won't notice any acceleration. Such a device is built to react to 'forces' acting on it and there is no force acting. Its 'spring', or equivalent, won't compress due to an external force, like an rocket-engine accelerating it, as long as it's following a geodesic.
As I sees it, when observed from being at rest with the 'frame of Earth' time have to be 'as always' for both me and the apple, as well as the distance(s) observed as we all are in the same 'frame of reference'? The apple falling will observe no 'stretched time' due to the gravity, and neither will I, sitting on the surface watching it? So he must mean if observed from some other 'frame of reference' right? Somewhere free from the gravitation. So let's make it a neutronstar then, and let us observe the apple from some position safely outside the stars gravitational 'field'.
Now, as that apple is 'free falling, the 'clock-ticks' I observe will have a longer interval. You can if you like equalize the apples 'slowing down' to a larger distance, but then you will have to ignore what you actually see, and make the 'slowing down' that imaginative equivalence to a longer distance.
But you also seems to need to see the apple accelerate somehow? "but as it approaches the planetary object the time scale stretches at an accelerated rate, giving the appearance that it is accelerating". From what frame is this? Although the apple in reality should slow down due to the clock-ticks intervals growing, when seen by me outside its gravitational field? And, in the end be 'standing still' more or less as observed by me. Nah, it makes no sense?
What I expect to see is the apple taking a longer time covering the same distance.
So, what does he mean?
and from what frame comes this observation he talks about?
I can see it as an abstraction, or as a thought up 'equivalence', as you could express it as growing distances instead, with the time being 'universally the same' but it have no bearing to what I actually would expect to see?
Hope my question makes sense.
That description was unreal to me, and frankly f*ed with my mind.
Or, what am I missing here?
==
Forgot to write in the link.
Hmm, now it will make sense :)
Maybe, I'll have to reread it again I guess ::)).
-
Crikey Yoron! I should have known better than to read your post. Now my brain hurts.
However, I think I see "word trick" here:
"This is why an accelerometer in free-fall doesn't register any acceleration; there isn't any."
The reason an accelerometer does not register acceleration in free-fall is because it's mass thingy (all accelerometers have to have a mass thingy in order to work) is subject to the same gravitational force as the vehicle to which it is attached. An accelerometer really measures the difference in acceleration between its mass thingy and the thing it's attached to. It does not measure absolute acceleration.
Anyway, I'm sure that if I say that loud enough, somebody will believe me.
To retrieve what little is left of my sanity, I will now go and torture more innocent pieces of metal. Viz.
-
Yor, may I ask where you read this?
-
It's in the link Yoron posted. Here's the longhand version.
http://en.wikipedia.org/wiki/Equivalence_principle#Development_of_gravitation_theory
-
Sweet stuff Geezer. Have to think a little on how you mean but hopefully I'll get it :)
That hydraulic was extremely clever (But the fluid have to get very hot I guess as the rotational pressure builds up?:) And yeah, it's in the link Ron. But it makes little sense to me. Especially in a wiki I like things to make sense, they don't need to be 'dumbed down', but they sure need to validate and explain in a manner that allow us to understand how they thought.
It makes some sense to turn time into distance, after all, distance builds on time. And that's how I read it at first, thinking he meant that he treated time as a measurable 'distance'. But rereading it I realized I didn't understand it at all, and that I had allowed my own preconceptions come in between.
"but as it approaches the planetary object the time scale stretches at an accelerated rate, giving the appearance that it is accelerating". H O W ?
::)) let me show you..
| | | | | | | ---> E a r t h <---
ok, we got the 'stretching time-scale ready here, right :) so, now we just need to understand how the *** It will be seen as accelerated, and from which 'frame of reference' :)
(my apple) ->0 | | | | | | | ---> E a r t h <---
Don't know this mysterious 'frame' but as I read it I will both see the 'time' elongate :)
As well as see that dam* apple either pass each 'time-line' at the same pace or? Even more amazing, speed up?
I didn't know of this frame of reference before?
What's it called?
==
It do make sense if you just look at the graphic, assuming a equivalence between time and distance, also letting the 'pace of the apple' be the same at all times (like some 'universal' time piece), but it's a word trick to me as there is no such frame. Mathematically you can treat it like this, I'm sure on that, but then point out that it's only a way of visualizing an idea. In reality you won't observe those effects from any 'frame of reference', even though they make a 'cerebral sense' :)
But it do highlight the mystery of 'distances'.
Now, if you want you can make the 'universe' such that this concept existed. Letting 'relative time' be exchanged for distances, but you need to remember that it builds on our 'relative' universe, then transforming that concept of time and distance into 'only distance'. And that universe would look very strange, very quickly, with mass and motion if you tried to illustrate it.
A ---Distance to--> B
Now assume that B is accelerating near light towards A here.
B--->A (allowing for both time dilation and speed)
B->A (exchanging the idea of a 'time dilation' for B relative A to an even shorter distance)
And you have to remember that as I exchanged that 'slow time' to the new 'universal time', the real effort it would take to make the way to A for B would be the same. This is just my very un-scientific graphical way of illustrating it, 'speeding up' B:s time in exchange for a 'shortened distance'.
(Don't really know if this would work though?
But the idea sure is intriguing :)
That's B:s 'distance' to A, no, not due to him having a Ferrari, it's the real 'distance' for B, due to relativistic effects as he speeds up. Now make me a painting of that, giving me all three views simultaneously.
And then the real mystery. Imagine that we are at C watching A and B. Now we will see them both, and to us they will get yet another relation distance-wise, but both will fit comfortably inside our 'frame of reference' giving us a 'whole SpaceTime' just as any of theirs 'frames of reference' will present them an alternative 'SpaceTime' just as whole with all of us fitting inside it perfectly.
Ehh, how many 'simultaneous' views do we get now?
A, AB, AC, (ABC - ACB) B, BA, BC, (BCA - BAC) and C, CA, CB, ((CBA - CAB) which is like a Ferrari, only, with the top off.) A and B and C own 'internal time' inside their respective 'frame of reference' is absolutely the same to me, and that's why I lifted it in as A & B & C at first above, as that's our reference of the 'intrinsically unchanging time reference'. So treating it like that you will get 1 + 2 views for each one. Or, you can use only the whole view and get two views (A and ABC f.ex), alternatively you can use 1 + 2 + 1 with 1 being that last 'whole view' for each one. Take your pick, it all depends on how you observe it, well, as I see it :)
Now think of neutron star instead :)
It would be a 'round' object to us normally, right?
Well, not if you exchange time for distance, it wouldn't.
That star would become a very weird object to look at.
-
Your links always hurt my head, Yor_on.
What the equivalence principle basically says is that any experiment you perform in a freely falling reference frame is identical to being in an inertial reference frame in deep space (i.e. one that's moving at a constant velocity). This could also be stated that space-time is curved, but tiny patches of it look flat if you're free-falling.
I think the point they're making about the time scale "stretching" is something like this: From your vantage point in deep space, you measure your geodesic to the earth and say "from here, it would take me 10 time steps to reach the earth if I were moving at a constant speed (in an inertial reference frame)." Then you start free falling. After falling 1 time step, you look down and say "Oh my goodness, my clock has changed! What was 1 time step worth of distance has stretched to 2 time steps worth!" Etc. I think "stretching" in this sense means that each "tick" is worth more distance along your path as you get closer to the earth.
I'm not sure if that's clear. It's starting to make sense to me, but I don't think I understand it well enough to really explain it any clearer than mud...
-
Yes, I think i see how you mean, you could look at as 'pressure zones' too I guess :) well, sort'a? Each 'zone' bending space a little more all the way down to the surface. What I was reacting too was the 'muddyness' (Not a bad word that one:) in defining from what frame he saw it, as well as the wording in itself making it weird. So, you're saying that he didn't exchanged it to distances then? :(
Sad, I liked that one :)
Made me think, I think ?
Ah well, better luck next time :)
-
Your links always hurt my head, Yor_on.
What the equivalence principle basically says is that any experiment you perform in a freely falling reference frame is identical to being in an inertial reference frame in deep space (i.e. one that's moving at a constant velocity). This could also be stated that space-time is curved, but tiny patches of it look flat if you're free-falling.
I think the point they're making about the time scale "stretching" is something like this: From your vantage point in deep space, you measure your geodesic to the earth and say "from here, it would take me 10 time steps to reach the earth if I were moving at a constant speed (in an inertial reference frame)." Then you start free falling. After falling 1 time step, you look down and say "Oh my goodness, my clock has changed! What was 1 time step worth of distance has stretched to 2 time steps worth!" Etc. I think "stretching" in this sense means that each "tick" is worth more distance along your path as you get closer to the earth.
I'm not sure if that's clear. It's starting to make sense to me, but I don't think I understand it well enough to really explain it any clearer than mud...
How JP? Are you saying that for a free-falling observer the distance will he travels per 'clock-tick' will increase per f.ex meter fallen? Oh yes :)
But if you're saying that he observes his 'space growing' due to him being in-falling towards a gravity-well? Then I'm having a little trouble seeing it? As I understands it the free-falling observer will see the distances as they 'really are' in his frame? Isn't it the far observer that will observe 'Space and time' change relative the near (free-falling) observer?
"but as it approaches the planetary object the time scale stretches at an accelerated rate, giving the appearance that it is accelerating"
That sounds as if one would observe the in-falling observer to me, not 'being him'?
And even if one was that in-falling observer one wouldn't observe time slowing down, well, there are those 'near death experiences' of course where people find time 'slowing down' :) but still?
Free-falling you sure will find that you cover a larger distance at each 'clock-tick', if that is what he meant. But it's no deformation of SpaceTime, well it is, but it's the 'normal' deformation that you will see in any frame where you are free-falling, following a geodesic (towards a gravity well that is, ah, can a orbit be treated as an acceleration too, btw? :)? And it's no 'appearance' either, from the point of view of the free-falling observer it's very real, as confirmed by the impact.
Sh* I'm not sure how to see this one. It's more or less the question if any 'distance' can be described a 'straight line', right :) and it makes sense, in a weird way. But he still could have expressed it clearer.
==
You could of course say that the closer to a gravitational surface you are, the slower your time will be. But that's wrong.. The time you refer to as 'slower' will only be so when compared to another frame of reference as I understands it. Are he saying that my 'intrinsic time' will differ depending on mass/velocity/speed, no 'frames of reference' needed to define it?
It's not only your head that hurts here JP :)
=
That one seems impossible to prove?
But can one disprove it?
We can prove that it's true as compared between 'frames of reference' as I understands it. But to say that we all 'age' differently, as we then should do? That would make 'times arrow' something intrinsic not only to me but to my atoms all the way down to the Planck-level. How the he* do we keep together as they all should have a different set of 'times arrow' depending on mass, relative speeds etc?
Also it introduces a circular logic it seems to me?
-
On another level this is exactly why I wonder about where 'frames of reference' ends and gets defined. It may seem a subtle difference, that either time-dilation only can be decided between 'frames of reference', or, that no 'frames' are needed and time-dilation is taking place in your body, now and forever.
It questions the idea of 'my personal frame of reference' as I sees it? Then we can't have a even 'intrinsic times arrow' at all it seems to me, only a approximation? And all evaluations between frames becomes 'muddy' as we then don't have any 'real frames' to compare between, if you see how I reason? that's why I like the concept of having it true only as a definition between 'frames of reference', but, that's also why I would like to understand how we define where they 'start' and 'end' better?
-
I read this but I'm not sure of how to understand it?
"Objects in free-fall really do not accelerate, but rather the closer they get to an object such as the Earth, the more the time scale becomes stretched due to spacetime distortion around the planetary object (this is gravity). An object in free-fall is in actuality inertial, but as it approaches the planetary object the time scale stretches at an accelerated rate, giving the appearance that it is accelerating towards the planetary object when, in fact, the falling body really isn't accelerating at all. This is why an accelerometer in free-fall doesn't register any acceleration; there isn't any." From Equivalence principle (http://en.wikipedia.org/wiki/Equivalence_principle#Development_of_gravitation_theory)
I believe that article has forgotten to highlight one important factor: that the falling object has non-zero size.
Because the falling object has non-zero size, there is both a spatial and temporal gradient along the object's length in the direction of the gravitational source i.e. downwards, so in such a situation, where there's any degree of space-time gradient, there will be an energy gradient along the length of the object and it will not be in equilibrium with itself. Thus, because the object is in a space-time gradient, it thinks it's already moving (for the front and rear of the object are in different frames of reference) and so actually starts moving and falling in an effort to become stationary and restore equilibrium along its length.
-
(But the fluid have to get very hot I guess as the rotational pressure builds up?:)
Off topic: Yoron - It's fluid velocity that generates most of the heat.
-
Kind'a loved that one LeeE, thanks.
And yes, taking those 'frames' to their extreme it seems as nothing can be in equilibrium?
Ahh, I like science :)
-
As we're discussing highly esoteric principles here, understandable by only the most enlightened broad-minded seekers of the holy grail. Ah, that would be me, and, you naturally :)
Yes, naturally shy..
And meek.
Anyone remember the recent discussion about electrons? Where I linked some physicists saying that they could be seen as superpositioned in their orbitals? Well, reading 'The Inertia of Energy' (http://www.mathpages.com/rr/s2-03/2-03.htm) I came over this golden pearl as we might say in Sweden (but won't). And I would love to cite it all, but i will limit myself to this
"The ability of electrons and anti-electrons (positrons) to completely annihilate each other in a release of energy suggests that these actual massive particles are also, in some sense, bound states of pure energy, but the mechanisms or processes that hold an electron together, and that determine its characteristic mass, charge, etc., are not known." That seems to go hand in glove with the idea of them being 'super positioned'? And my question then must be, how do they become 'confined'?
Just had to show it, others may collect memorabilia, I quotes :)
-
The idea of farsight's torus shaped electron comes to mind and seems to fit. With the proton situated at the center of the torus the electron would seem to exist in any of it's energy states and fit Heisenberg's uncertainty Principal.
-
I'm sorry Ron, I can't but help wonder whose principal you are referring to?
Heisenberg's? That wouldn't, by any chance, be his headmaster?
Sorry again, I couldn't help that one :)
A very sick humor is mine.
Anyway, What I cited about in form of 'energy' we do well to realize that there exist no definition for that, we talk about 'virtual photons' but as I understands it only as the 'carriers' of energy, not as the 'energy' itself? There seems to be a difference there. The closest I've understood it to be is some 'kinetic force'? Although I have trouble seeing how it can get transferred outside of Planck time, as I understand those 'virtual particles' to be?
I do believe photons to be the same as the 'vacuum energy', and those 'pimpernel virtual ones' too :) There I suspect 'times arrow' to be the joker. But I think of it as a 'unmoving field' more or less, well, for now I do at least :) with the 'interactions' creating what we observe as our apparent motion in SpaceTime. And as all those 'interactions' are made under and perceived through our 'arrow of time'. Then that's also why I want to understand as much as I can wherefrom that weird arrow comes, and how it expresses itself. And there the rest of my questions jumps in too. But I don't have any explanation for what makes a singular 'photon' as we observe it, more than it have to be something involving the way we observe and live inside 'time', or its 'arrow' as I like to see it. As for a torus? I think that discussion belongs under 'new theories' as it's not wondering's as much as it is a try for a new theory of the 'universe and all'. I don't have any such theory, just guesses :)
You could think of it in form of densities, some thicker some vapor, and then say that they all come from the same thing, whatever that is? Kaa :) But you would still have to explain the densities coherence in time, also explain why some of them have a 'free will' and can choose a motion, keeping themselves intact. You can and will make choices, involving motion and thoughts, you have a 'history' that also works as a 'pointer' into the 'future' as the chaos maths 'patterns' shows us, as they will wait for us there, unchanging constants no matter your, and mine, individual choices. So taken all together it's a mystery to me :)
-
Let me give you an example on how I wonder Ron.
Taste :)
I have it, you have it, most of us do. But what is it?
As I understands it 'taste' is the way certain molecules fit 'receivers' in f.ex our tongue.
So? Have we now explained taste?
It's the geometric 'formations' of 'molecules' in SpaceTime fitting your tongues receptors :)
SH* no, as I see it we haven't even started to explain it.
Why would a given geometric shape give me that sweet sweet taste of Sugar? And, the taste seems 'universal' too :) That is, all animals we know will immediately recognize it for a substance they enjoy, more or less :) How can that be? Are we preprogrammed to 'enjoy' certain molecules, and also to recognize them the first time we taste them? Or is that a learning process? But we all like it, so in some way we do have a common nominator somewhere it seems?
And any theory that won't consider consciousness as a prerequisite for the questions it thinks that it answers will be in the same situation, explaining without explaining. We 'isolate ourselves' from the universe as we look at those 'smallest constituents'. It's a standard scientific procedure to try to be 'objective' and 'isolate' the 'system' you want to observe, and it makes a good deal of sense when defining and describing different causality-chains. But in the larger perspective, what is it we want? isn't it to understand why we are here, how we come to be, how we can be the ones able to question it all? Some people answers this with God, others may try to find more 'objective' answer involving 'particles' or 'waves', but when one bind oneself to only one answer one also constricts oneself. In that sense modern science are no different from religion, in that both camps have a 'reducible philosophy' wanting all things to come from one, or at least as few as possible.
We have a lot of preconceptions, and even when we realize that they are wrong we still treat them as being the ones important. Like the way we like to treat non-linearity, we admit that linearity is just a 'spec' in an ocean of non-linearity but we still treat it as if that ocean of non-linearity can be constricted, and in that way become subordinate to linearity. We also use arguments expecting the simplest compatible 'truth' to be the one the universe choose. Doing so we seem to miss that if we find two 'truths', both fitting our experiments, then perhaps both are valid?
There is a lot of things we do that I expect to come from preconceptions but we still have to start somewhere, and the way we isolate systems to see as clearly as we can is that start. But to expect the universe to bend to linearity I believe to be a big mistake, as big as believing that the universes logic is 1+1=2. JP points out that we differ between SpaceTime in that we in one way define solutions from a 'constricted area' ignoring the way SpaceTime 'bends' to gravity, in another we define different solution using SpaceTime 'bends'. So does this feel like a answer? Splitting it in two, depending on the questions asked? Well, maybe it does, isn't that our usual linear way of treating non-linearity? Creating a cut-off and then state that 'considering those' the solution will be **?
Like that scientist getting hired by the dairy farmers to come up with new ways to increase milk production? "Consider a spherical cow"
So, do anyone expect that there will come to be that 'ultimate cut-off(s)' explaining our universe?
No. Don't think so myself, we will need other ways of explaining super-positions, probability, chaos, non-linearity. And in that motto I don't expect the universe to be able to be reduced to some 'single force' from where it all builds. But those are all my own opinions of course :)