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Expansion of our universe (solar system).
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08-11-2011 6:07pm#1
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I think at a local level (within clusters) gravity is the main player so there is no expansion until you get past a certain distance between objects, if this is correct then a good question is "at what distance does expansion overtake gravity", I can't find an answer to that (It might not even be a valid question).rccaulfield wrote: »Surely then my point stands. For example with Special relativity, you can see the satellites whizzing around the earth experience time at a different rate at the micro second level. Point being surely the expansion doesn't just begin all of a sudden it must be present at the minute level and taper up as the distance between the objects increases? As for the gravity well example, there are experiments i've seen where small balls of iron are gravitationally attracted to each other so big mass is not needed to actually see the theory at work-not being confrontational just wanna get into the nitty gritty of this theory.
All the talk of 4th dimensions etc has most people i know rolling the eyes cos you may aswell be talking about chakras etc. Whats observable and provable at our solar level? This is still a vast vast amount of space for me!
The universe expands at a rate of 73.8 km/sec/mega-parsec*.
(1 parsec = 3.3 ly) so 73.8km/sec over 3,300,000 lys
With a rough calculation (which is not my strong point, so it could be totally wrong, all those 0's confused me
) that would make .00738 mm/sec per 3,135,000,000 kms. Neptune is roughly 4,500,000,000 kms away.
*+/- 2.5
(73.8 kms/sec per 3,300,000 lys = 738mm/sec per 33 lys = 738mm/sec per 313,500,000,000,000 kms =
.00738mm/sec per 3,135,000,000 kms)0 -
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Cú Giobach wrote: »I think at a local level (within clusters) gravity is the main player so there is no expansion until you get past a certain distance between objects, if this is correct then a good question is "at what distance does expansion overtake gravity", I can't find an answer to that (It might not even be a valid question).
The universe expands at a rate of 73.8 km/sec/mega-parsec*.
(1 parsec = 3.3 ly) so 73.8km/sec over 3,300,000 lys
With a rough calculation (which is not my strong point, so it could be totally wrong, all those 0's confused me) that would make .00738 mm/sec per 3,135,000,000 kms. Neptune is roughly 4,500,000,000 kms away.
*+/- 2.5
(73.8 kms/sec per 3,300,000 lys = 738mm/sec per 33 lys = 738mm/sec per 313,500,000,000,000 kms =
.00738mm/sec per 3,135,000,000 kms)
Thank you! So is it safe to say that an expansion of 00.8mm per second is occuring between earth and Neptune in your opinion?AugustusMinimus wrote: »Even at solar level, the expansion of the universe must have an affect IMO.
If there is no force placed on two objects and if the universe expands between them, then it is natural for the two objects to fly apart. However, while this is happening, there is no actually force being placed on those objects as technically, the objects are not moving through space.
If gravity were to hold them in position relative to each other and if space were to expand, then even though they are not moving relative to each other, there would be a force placed upon them as they are overcoming the the expansion of the universe.
IMO, gravity interferes with all of this but doesn't completely erradicate it.
There are a lot of theories wether the universe if perfectly fluidic of quantized (broken into blocks). Some think the fabric of space is broken into blocks of plancks length. If this is true, then the expansion of space happens one plancks length at a time, with extra sections being slotted in.
Irrelevant to this, it means that the expansion of the universe happens on a microscopic level as well as macroscopic level. THis must mean that the expansion must put a force even on atoms as the universe expansion would try to seperate electrons from the nucleus.
So simple question left is does the expansion at solar level present itself as something observable and that can be differentiated from the strong force and or gravity? If not then whats the magic distance that the expansion becomes observable?As for your point about atoms - well the force holding atoms together - the strong force (as well as the weak force and the electromagnetic force) is much much stronger than the force of gravity. The effect of gravity on the binding force between atoms is really unbelievably tiny. This is why people at the LHC in CERN do not need account for gravity in their calculations.0 -
Norccaulfield wrote: »Thank you! So is it safe to say that an expansion of 00.8mm per second is occuring between earth and Neptune in your opinion?
I don't know enough on the topic to be making definitive statements.
If it is though there is now way of observing it because nothing is moving due to it at this level, it can only be measured at a very large scale.0 -
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That would be 25km/year. That would be fairly noticeablerccaulfield wrote: »Thank you! So is it safe to say that an expansion of 00.8mm per second is occuring between earth and Neptune in your opinion 0 -
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That would be 25km/year. That would be fairly noticeable
The figure was .00738mm not 00.8 that would make it 230 meters over a year.
I'm sure someone will come along and show how my reasoning there is flawed, so please don't take those figures as gospel folks.
Even if it was 25km it wouldn't be noticeable because it wouldn't affect anything.0 -
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Cú Giobach wrote: »The figure was .00738mm not 00.8 that would make it 230 meters over a year.
I'm sure someone will come along and show how my reasoning there is flawed, so please don't take those figures as gospel folks.
Even if it was 25km it wouldn't be noticeable because it wouldn't affect anything.
Of course it should be noted that since the planets are in bound orbits they will correct for the expansion of the universe. If they were unbound then your calculation would be fine.0 -
That would be 25km/year. That would be fairly noticeable
The expansion of the universe is not linear.
The closer together two points are, the slower the expansion. It's the accordian effect.
There's also the point that neptune's and the earth's orbits may be the way they are due to the small expansion that happens.0 -
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the whole point of the discussion here was to talk about that! have a read first and if you're puzzled i'll try and help
I ''followed'' the thread long before I commented on it as I find it fascinating. Unfortunately my current workload does not allow me time to dig out all my physics books and get into in depth dicussions on this particular topic :mad: . I'll return to the thread at a later date Just thought I'd get to this point about local measurement e.g perhaps detecting the effect of expansion on a small controllable mass in a lab. 0 -
I ''followed'' the thread long before I commented on it as I find it fascinating. Unfortunately my current workload does not allow me time to dig out all my physics books and get into in depth dicussions on this particular topic :mad: . I'll return to the thread at a later date Just thought I'd get to this point about local measurement e.g perhaps detecting the effect of expansion on a small controllable mass in a lab.
Afraid that wouldn't be possible at such length scales/mass scales. I should clarify- Certainly within our solar system it is possible to do test of General Relativity. It is the expansion of the universe that is in question. The test case in this thread of Earth-Neptune shows how tests for the expansion on such relatively small scales is not possible.
Since I don't know your background I'll try and outline what we do know.
How then do we know the universe is expanding? Well you can see it in the fact that stars look red on average. The reason for this is similar to what happens when an ambulance passes by you at speed. Just as the frequency of the siren sounds decreases as the ambulance moves away - or in otherwords the wavelength of the sound increases -, the wavelength of light increases if the source (galaxy) is moving away. Long wavelength light corresponds to red light.
When we look through a (pretty good) telescope at the night sky more of the stars appear red than others.
Well is there any other evidence? Yes. Extrapolating back to early time has led to the big bang proposition. An amount of radiation should be left over from this early time when the universe cooled down (i.e. expanded enough) for the photon radiation to stop getting sloshed around by electrons. The cosmic microwave background exists for almost all the expansion of the universe and so shows signs of the expansion. It has been detected and is fully consistent with these other measurements. So this is a prediction that has borne fruit. Note if you go to a static channel on your tv that up to 10% of the static is due to the cosmic microwave background.
Any more? Yes! The abundance of Hydrogen, Helium, etc that pervades the universe can be predicted within this big bang model. The prediction and the amount observed agrees unbelievably well (this is called big bang nucleosynthesis).
Ok here ends the crash course!0 -
Thanks.Well yes but for all intents-and-purposes it is way too small to be noticable ... see the earlier post about the scale difference -> Hubble scale is around 3000Mega pc. To get an idea of this scale: Distance to Proxima Centauri (nearest star other than the Sun) is 1.3 pc. Size of Milky way is around 30 Kilo pc.
Your corrected calculation of around 300 metres/year sounds about right. This is a correction in the distance to Neption of
300/(4.4*10^12) *100/1 % per year i.e. a correction of around 7*10^-9 % per year in the distance between Earth and Neptune - certainly far too small to be noticed!
By the way, it's not a corrected calculation it's the original and not to sound offensive but don't you think someone who can (and would) do a quick calculation of the rate of expansion to the distance of Neptune, might have a rough idea of the size of the universe and the distances to the stars.
To me the rate is actually quite large, I stopped viewing the very large or very small on a human scale decades ago.
Edit: I thought that number seemed quite large, it works out at around 2.5cm per year at the distance to the moon, not far off the measured rate of the moons recession due to tidal forces.0 -
Cú Giobach wrote: »Thanks.
By the way, it's not a corrected calculation it's the original and not to sound offensive but don't you think someone who can (and would) do a quick calculation of the rate of expansion to the distance of Neptune, might have a rough idea of the size of the universe and the distances to the stars.
To me the rate is actually quite large, I stopped viewing the very large or very small on a human scale decades ago.
Edit: I thought that number seemed quite large, it works out at around 2.5cm per year at the distance to the moon, not far off the measured rate of the moons recession due to tidal forces.
Cú Giobach when I said 'your corrected calculation' I made a typo. I meant to write 'your correct calculation' - as opposed to that of seamus. Your comment is not offensive. Rather it is unnecessarily defensive. The mentioning of scales to the stars and size of the universe was not for your benefit. It was for the benefit of others that might be reading the thread. Tbh I don't appreciate your censure on this point and I don't understand why you'd want to do so. I might be one of the few others on the site that might know what they are talking about - when it comes to this topic - as well. :cool:0 -
Sorry i placed the decimal at the wrong zero:rolleyes:Cú Giobach wrote: »The figure was .00738mm not 00.8 that would make it 230 meters over a year.
I'm sure someone will come along and show how my reasoning there is flawed, so please don't take those figures as gospel folks.
Even if it was 25km it wouldn't be noticeable because it wouldn't affect anything.rccaulfied... not to sound harsh but please read the comments i've already posted about how negligible the expansion of the universe must be for masses that are clumped together - such as our universe.
Anyway, An estimate for the scale at which you should be able to observe the expansion of the universe is given by the Hubble radius - below this distance it's pretty safe to ignore the expansion of the universe. The value of this today is around 3000 MegaParsecs. The entire observable universe today is roughly 14000 MegaParsecs (note 1 parsec is roughly 3.26 lightyears) so that gives you an idea of the sort of scales you need to observe this phenomenon.
PS there's a really good FAQ section here http://www.astro.ucla.edu/~wright/cosmology_faq.html#DN
This probably gives clearer descriptions than I can give!
Never mind noticed, can it be observed? I mean using Cern type technology here, out at the distance of Neptune or closer if practical. For me if its not observable at solar level, thats a problem for the general publics acceptance of it. I mean the cmb IS there, the stars etc ARE red shifted on average but they are results of something. Not observable causes. So 3000 mega pcs eh, what galaxy is out around there?Well yes but for all intents-and-purposes it is way too small to be noticable ... see the earlier post about the scale difference -> Hubble scale is around 3000Mega pc. To get an idea of this scale: Distance to Proxima Centauri (nearest star other than the Sun) is 1.3 pc. Size of Milky way is around 30 Kilo pc.
Your corrected calculation of around 300 metres/year sounds about right. This is a correction in the distance to Neption of
300/(4.4*10^12) *100/1 % per year i.e. a correction of around 7*10^-9 % per year in the distance between Earth and Neptune - certainly far too small to be noticed!
What do you mean about the moon thats the observed expansion if all other forces didn't exist?Cú Giobach wrote: »Thanks.
By the way, it's not a corrected calculation it's the original and not to sound offensive but don't you think someone who can (and would) do a quick calculation of the rate of expansion to the distance of Neptune, might have a rough idea of the size of the universe and the distances to the stars.
To me the rate is actually quite large, I stopped viewing the very large or very small on a human scale decades ago.
Edit: I thought that number seemed quite large, it works out at around 2.5cm per year at the distance to the moon, not far off the measured rate of the moons recession due to tidal forces.0 -
I guessed that, that's why I didn't mention it when you first said itrccaulfield wrote: »Sorry i placed the decimal at the wrong zero:rolleyes:Never mind noticed, can it be observed? I mean using Cern type technology here, out at the distance of Neptune or closer if practical. For me if its not observable at solar level, thats a problem for the general publics acceptance of it. I mean the cmb IS there, the stars etc ARE red shifted on average but they are results of something. Not observable causes. So 3000 mega pcs eh, what galaxy is out around there?
The expansion has no effect on "clumps" ie: galaxies or clusters of galaxies, solar systems, planets...etc because space itself is frictionless.What do you mean about the moon thats the observed expansion if all other forces didn't exist?
Lets just think of two gravitationally bound objects (the same also applies for the other forces, nuclear and magnetism), the space between these two objects is expanding but because space is frictionless there is no actual force operating on these objects due to the expansion, so they wont be pulled apart against the force of gravity that connects them.
Imagine two of those moving walkways you see in airports but made of ice, think of two people, one on each and travelling in opposite directions, if these people reach out and hold hands they will stop moving as the walkways slide away beneath them, if the walkway was completely frictionless even the slightest force (ie; the two people connected by a spiders silk thread) wouldn't get them moving. (This analogy isn't completely accurate, no analogy is, but I think it gives a very basic idea of things).
The observed expansion only happens at a scale where the universe is homogeneous and there are no unequal forces acting on things.
If space was a tangible "thing" like say treacle, then the expansion would impart a force that objects would have to resist in order to remain in position relative to each other.
That's my take on it.
Just to add, I think when people talk about space stretching or new space being created it gives the wrong idea, space is just that "space", the recession we view isn't objects being carried along by something, more like an inherent motion, I think you could almost say, they are not receding because space is expanding, but space is expanding because they are receding, with energy "welling up" filling the void.0 -
Cú Giobach wrote: »I guessed that, that's why I didn't mention it when you first said it
The expansion has no effect on "clumps" ie: galaxies or clusters of galaxies, solar systems, planets...etc because space itself is frictionless.
Lets just think of two gravitationally bound objects (the same also applies for the other forces, nuclear and magnetism), the space between these two objects is expanding but because space is frictionless there is no actual force operating on these objects due to the expansion, so they wont be pulled apart against the force of gravity that connects them.
Imagine two of those moving walkways you see in airports but made of ice, think of two people, one on each and travelling in opposite directions, if these people reach out and hold hands they will stop moving as the walkways slide away beneath them, if the walkway was completely frictionless even the slightest force (ie; the two people connected by a spiders silk thread) wouldn't get them moving. (This analogy isn't completely accurate, no analogy is, but I think it gives a very basic idea of things).
The observed expansion only happens at a scale where the universe is homogeneous and there are no unequal forces acting on things.
If space was a tangible "thing" like say treacle, then the expansion would impart a force that objects would have to resist in order to remain in position relative to each other.
That's my take on it.
Just to add, I think when people talk about space stretching or new space being created it gives the wrong idea, space is just that "space", the recession we view isn't objects being carried along by something, more like an inherent motion, I think you could almost say, they are not receding because space is expanding, but space is expanding because they are receding, with energy "welling up" filling the void.
I wouldn't agree with that.
Any matter in the universe with mass will oppose being accelerated. You need a force to change the direction of movement of an object.
If as you say, matter is sliding space slide past it, then it means that the matter is moving through space without any force acting upon it. This doesn't make sense.
To my mind, space will carry matter along with it. If it didn't, it would be breaking Newtons 1st law of motion.
On solar scales, the expansion of the universe is negligable, with gravity a much bigger player.
On the molecular and atomic level, the forces at play completely over ride any effect the expansion has on matter. Electrons for instance are either in an electron shell or they are not.0 -
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To get back to the minumum distance that the expansion can be observed- 3000 mega parsecs. Andromeda is less then 1 mega parsec away so this rules out alot of the galaxies we are familiar with. Question arises, are the majority of things within this range blue shifted or not biased toward being red and blue shifted? I'd expect them certainly not to biased toward being red shifted if the expansion doesn't hold within this range and so gravity at the galactic scale can work unimpeded? Space is frictionless so expansion is over ruled by local forces, i like that way of thinking of the expansion, i'll leave my brain mull over that one.Cú Giobach wrote: »I guessed that, that's why I didn't mention it when you first said it
The expansion has no effect on "clumps" ie: galaxies or clusters of galaxies, solar systems, planets...etc because space itself is frictionless.
Lets just think of two gravitationally bound objects (the same also applies for the other forces, nuclear and magnetism), the space between these two objects is expanding but because space is frictionless there is no actual force operating on these objects due to the expansion, so they wont be pulled apart against the force of gravity that connects them.
Imagine two of those moving walkways you see in airports but made of ice, think of two people, one on each and travelling in opposite directions, if these people reach out and hold hands they will stop moving as the walkways slide away beneath them, if the walkway was completely frictionless even the slightest force (ie; the two people connected by a spiders silk thread) wouldn't get them moving. (This analogy isn't completely accurate, no analogy is, but I think it gives a very basic idea of things).
The observed expansion only happens at a scale where the universe is homogeneous and there are no unequal forces acting on things.
If space was a tangible "thing" like say treacle, then the expansion would impart a force that objects would have to resist in order to remain in position relative to each other.
That's my take on it.
Just to add, I think when people talk about space stretching or new space being created it gives the wrong idea, space is just that "space", the recession we view isn't objects being carried along by something, more like an inherent motion, I think you could almost say, they are not receding because space is expanding, but space is expanding because they are receding, with energy "welling up" filling the void.0 -
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