How do we compensate for acceleration?

[Workboots]

Hi all,

Thank you for taking the time to read this post, but I am a layman, so please bear with me.

My question refers to observing distant celestial bodies in relation to our position on a moving body. Since the earth is accelerating, is there a theoretically fixed point relative to which we can mark our observations, or if no such point exists, is there a mathematical compensation for the earth's motion? In short, is it possible to treat the earth as stationary for the purposes of mapping the stars?

Any insight would be much appreciated, be it articles or opinions.

Thanks again,

Workboots

[ronin]

No I suppose is the answer.

We are moving but distances are so great that in a lot of cases we cannot be sure by how much relative and in quite a lot even which direction relative.

Observe even Mars and to us it moves forward, slows down, stops, moves backwards, slows down and starts to move forward again.

Now MArs is easy, we have been looking at Mars for a few thousand years, Roman called it Mars, Greeks called it Aries. So it is a very familiar body.

If you now consider a star some 500 lightyears away you have little chance. The movements are just too small in general.

They will map the stars in one of two ways - use Gaia data for apparent motions and so relative to earth, or, add in our suns movement and do everything including us relative the the galactic core Sag A most likely. Sag A being the big black hole thing at the middle.

Will say that Gaia data seems to be a lot rarer then I expected, so not sure how well or bad that is going, everything seems a bit too quiet with Gaia.

[Paul2015]

It could be possible,

But why?

[Floater]

It could be possible,

But why?

To answer with a question is always questionable, but: Why not?

[Workboots]

Thanks, ronin, for your quick and informative reply. I will search Gaia and Sag A for more leads.

In response to Paul2015, I'm wondering what the starchart would look like if we could observe it from a stationary position in our galaxy.

I'll be gone for the next 12 hours or so, but if anybody has more to add, I would love to know!

[Paul2015]

I'm confused :s

Your planning on mapping the stars from a singular point in space (I've got this much)

So your planning on mapping from a singular point in time? (Where you lost me)

The reason I asked why is as a lot of objects in space are in orbit or moving in some direction and to completely remove this would be impossible. See Penrose–Hawking singularity theorem.

When you say acceleration is it that of the earth or of other celestial objects?

What I mean is if you were to map a 2°^2 section of sky, your trying to factor out the acceleration of the earth or the objects being mapped or do you mean the earth's rotation?

If its the earth's acceleration is it the acceleration of the earths orbit of the sun? Or is it the sun's orbit of the milky way? Perhaps both maybe you even want to factor in for the earth being pulled ever closer to the sun? Perhaps the milkyway's acceleration towards Andromeda? Or the milkyways movement in space? The ever expanding universe from the big bang? It's just a whole mess of singularity theorem. Which is always changing as not even the worlds finest minds can figure that out, from einstein to hawking.

For example the earth's travelling at 30km/s around the sun, the sun's travelling at 200km/s around the galaxy and that's speed NOT acceleration. Acceleration as such isn't really what's important but rather centripetal acceleration which is the speed of an object to maintain a circular orbit. With this we can factor out the movement with our galaxy but that's it. To go further you'd have to explore the other galaxy's in relation to our own. Knowledge I don't have and you'll need a heavy understanding of physics to do so, if its even obtainable information.

As you can see its a very complex/ impossible calculation depending on what your trying to acheive. I can't quite be bothered to do the math right now but the your going to need to have something to factor it against. I'm not even sure if this is known for any objects out side of the galaxy.

Bottom line is from theoretical point of view its very difficult to do. If your absolutely sure you want to do it go for it. I'd love to see the results you'll probably gain a physics degree and masters and doctorate in the process

However to change the subject from theoretical physics to a more common sense approach. Back to the singular point in space idea such as that if you were to hop on a shuttle, don a spacesuit jump outside and stay right there. Take some pictures in every direction/axis then yes its possible. Just been done already check out any star map all these factor the rotation of the earth.

Then again I could just be completely wrong about what you want to do in which case none of this was relevant at all

[Floater]

Wow!

Honestly, I'm not being facetious, Paul. My earlier post, 'why not', was frivolous and meant to be light-hearted. And you're obviously not being frivolous.

Wow! Power to you.

[Paul2015]

Wow!

Honestly, I'm not being facetious, Paul. My earlier post, 'why not', was frivolous and meant to be light-hearted. And you're obviously not being frivolous.

Wow! Power to you.

Lol a serious answer to a serious question.

[Garethr]

Got to love this forum.

A question that I had to read twice before I understood it, and seconds later there are the detailed answers alongside the funny replies

Stephen Hawking you are missing out on a huge resource for your theories.

Respect to all out there.

Gareth.

[L8-Nite]

This site may be of interest.

http://www.sdss.org

[ollypenrice]

-The Earth rotates.

- It rotates inside an imaginary sphere upon which stars have relatively fixed positions from the distance at which we view them. Of course they are moving like crazy but, from our distance, this doesn't prevent us mapping them on an imaginary sphere.

- As we observe this imaginary sphere our night side rotates within it causing objects to disppear on one side and appear on the other. However, on our maps of this imaginary sphere we have projected the earth's axis and equator to define a notional grid and we have also defined an entirely arbitrary point (The First Point of Aries) which serves the same purpose as the Greenwhich Meridian. It fixes the celestial lines of longitude (called lines of right ascension) on the map of the sphere. So now we have a set of celestial co-ordinates allowing to define the relative positions of the stars.

- Alas the earth precesses and nutates (wobbles on its axis) so our projections of its axis and equator need to be redone every now and then, which is why star charts have an 'epoch.'

If your question lies outside the information above then forgive me, but I wasn't entirely sure what you were asking. If your point was that the earth is moving round the sun, the sun round the galaxy and that the galaxy, like all other galxies, is moving relative to other galaxies then, yes, you are right. And our charts are, in absolute terms, highly imperfect approximations. However, they are good enough to allow telescopes of immense focal length and miniscule field of view to find their targets with absolute reliability.

Olly

[Stub Mandrel]

The Universe must have a central point where the 'big bang' started. In theory it should be possible to work out where this is because as the universe expands the mass density or velocity distribution will be different depending on where you are relative to the centre. Problem is, it's so big that we see a more or less homogenous universe.

We are like a fish whose huge fishtank has broken. The water is surging outwards, but we can swim in any direction we want and can't tell whether we are moving away from or towards the the centre.

Assuming intelligent life arose in a galaxy at the first opportunity - they would see only younger galaxies unable to support life if they looked 'outwards' from the centre. Unfortunately, because light takes time to get to them they would also only see younger galaxies if they looked inwards as well so they haven't use that as a way to find the centre...

Lets travel to the edge of the universe,. as it expands. We look outwards, and see nothing as there is nothing to see. We look inwards, and there is nothing to see as light from the rest of the universe can't catch up with us yet...

Move in a bit and look inwards - we see,very faintly, the big bang! But turn around and look outwards and we see, very faintly, the big bang...

I suppose that the only way to fix that central reference point would be to be near the edge of the universe, but stationary compared to the centre, you could then more light coming from the big bang in the direction of the centre.

But how do you know you are stationary? Only by being able to see more light from the big bang in that direction. But if you randomly move in any direction you see more light coming towards you (like walking or driving in the rain).

So my guess is the only ways to find out where the centre of the universe is are (1) to know already so you can make yourself stationary with respect to it and (2) to be outside the universe and see where it comes from when it gets to you.

[michael.h.f.wilkinson]

The Universe must have a central point where the 'big bang' started. In theory it should be possible to work out where this is because as the universe expands the mass density or velocity distribution will be different depending on where you are relative to the centre. Problem is, it's so big that we see a more or less homogenous universe.

We are like a fish whose huge fishtank has broken. The water is surging outwards, but we can swim in any direction we want and can't tell whether we are moving away from or towards the the centre.

Assuming intelligent life arose in a galaxy at the first opportunity - they would see only younger galaxies unable to support life if they looked 'outwards' from the centre. Unfortunately, because light takes time to get to them they would also only see younger galaxies if they looked inwards as well so they haven't use that as a way to find the centre...

Lets travel to the edge of the universe,. as it expands. We look outwards, and see nothing as there is nothing to see. We look inwards, and there is nothing to see as light from the rest of the universe can't catch up with us yet...

Move in a bit and look inwards - we see,very faintly, the big bang! But turn around and look outwards and we see, very faintly, the big bang...

I suppose that the only way to fix that central reference point would be to be near the edge of the universe, but stationary compared to the centre, you could then more light coming from the big bang in the direction of the centre.

But how do you know you are stationary? Only by being able to see more light from the big bang in that direction. But if you randomly move in any direction you see more light coming towards you (like walking or driving in the rain).

So my guess is the only ways to find out where the centre of the universe is are (1) to know already so you can make yourself stationary with respect to it and (2) to be outside the universe and see where it comes from when it gets to you.

This is classic non-relativistic reasoning, based on our everyday perception of a 3D space and passing time. Note that this is not reality. It is simply a model we build in our mind based on sensory input and the workings of the brain. The nature of the model is no doubt one that is useful for survival (if I do not model that lion well enough it might eat me, after all ). It works well on our everyday space and time scales, but appears to break down horribly both on the cosmic and on the quantum scales. There was never any evolutionary pressure to evolve brains capable of intuitively modelling those scales. This is one reason why it is so easy to get things wrong.

Visualizing the big bang as an explosion centred on some point in space is done in many, if not all documentaries on the evolution of the universe. This is not how physicists perceive it. The big bang created space (or space-time) itself. The singularity was not at a specific point in space because there was no space. It is very difficult to get your mind round this concept, and mundane reasoning based on the classical idea of a centre of the cosmos gets you nowhere in this field.

I studied astronomy at uni, and in both quantum-mechanics and cosmology courses I developed a feeling for the mathematics of the problem, a mathematical intuition if you will, but the moment I tried to visualize things to develop a more natural intuition my monkey brain tended to get in the way.

[Stub Mandrel]

I was quite pleased to have an inkling of why the universe looks the same whichever way you look, regardless of where you are.

Ok then, answer me a couple of dumb questions that I have been stockpiling for when I get to chat to an astropyhsicist.

I realise the 'age of the universe' is meaningless at some levels, but lets accept it's about 13.5 billion years old.

In monkey brain mode:

Universe starts as a finite but huge amount of energy 'the singularity' at the start of time* this is tiny but unlike a point occupies a finite space. In less than a second this expands to the size of a grain of sand. This is enough to imprint quantum fluctuations in the singularity on the 'grain' and everything that follows.

Expansion continues at the speed of light for 13.5 billion years, but the universe isn't 27 billion light years + 1 grain of sand across, it's 90 billion (plus a grain of sand).

1) I often see this bigger than you expect' figure stated in a 'don't worry about the details as you won't understand them' way, but are you able to explain how this discrepancy is calculated. Is it time dilation as the light travels on its way?

2) If the universe started as a sphere and expanded why isn't it reasonable to imagine space-time as an ever expanding sphere bounded by an  ever weakening front of energy, even if the concept of a 'void' into which it expands is meaningless.

3) I have other questions, but I lack the vocabulary to express them

[Zakalwe]

The Universe must have a central point where the 'big bang' started. In theory it should be possible to work out where this is because as the universe expands the mass density or velocity distribution will be different depending on where you are relative to the centre. Problem is, it's so big that we see a more or less homogenous universe.

There is no centre- spacetime appears to be expanding everywhere. in other words, every part of it (on a macro scale) is expanding away from all other parts.

As for the point that the Universe "must have a central point"- why does it? The Universe is under no obligation to act as we expect it to. :-)

Lets travel to the edge of the universe,. as it expands. We look outwards, and see nothing as there is nothing to see. We look inwards, and there is nothing to see as light from the rest of the universe can't catch up with us yet...

Again, it is thought that there is no edge. An edge would imply that there is something beyond it, which most models suggest that there isn't. Then again, there may be multiverses!

But how do you know you are stationary? Only by being able to see more light from the big bang in that direction. But if you randomly move in any direction you see more light coming towards you (like walking or driving in the rain).

The concept of being stationary doesn't exist in spacetime. It is a Newtonian construct, along with a universal time which has been superseded with the idea of relative spacetime. Your movement and perception f the passage of time is only realtive to your frame of reference. observers in other frames of reference (ie inside a gravity well or moving at a different speed relative to your frame of reference) will perceive your time and location differently to how you do.

Expansion continues at the speed of light for 13.5 billion years,

It's actually expanding faster than the speed of light, which explains why there are parts of spacetime that we can never see. They are receding from us so fast that the light from them is red-shifted to infinity. This expansion does not contradict Relativity as Relativity does not forbid sapcetime from expanding faster than c

Expansion continues at the speed of light for 13.5 billion years, but the universe isn't 27 billion light years + 1 grain of sand across, it's 90 billion (plus a grain of sand).

1) I often see this bigger than you expect' figure stated in a 'don't worry about the details as you won't understand them' way, but are you able to explain how this discrepancy is calculated. Is it time dilation as the light travels on its way?

2) If the universe started as a sphere and expanded why isn't it reasonable to imagine space-time as an ever expanding sphere bounded by an  ever weakening front of energy, even if the concept of a 'void' into which it expands is meaningless.

3) I have other questions, but I lack the vocabulary to express them

1) Time dialtion (and length contraction and mass increase) is governed by the percentage of the speed of light the object is moving at relative to your frame of reference, as well as the size of the gravity well that it is in.

2) Spacetime doesn't have to be a sphere. http://www.universetoday.com/120157/what-shape-is-the-universe/  https://en.wikipedia.org/wiki/Shape_of_the_universe

3) I have a headache now!

[ollypenrice]

I was quite pleased to have an inkling of why the universe looks the same whichever way you look, regardless of where you are.

Ok then, answer me a couple of dumb questions that I have been stockpiling for when I get to chat to an astropyhsicist.

I realise the 'age of the universe' is meaningless at some levels, but lets accept it's about 13.5 billion years old.

In monkey brain mode:

Universe starts as a finite but huge amount of energy 'the singularity' at the start of time* this is tiny but unlike a point occupies a finite space. In less than a second this expands to the size of a grain of sand. This is enough to imprint quantum fluctuations in the singularity on the 'grain' and everything that follows.

Expansion continues at the speed of light for 13.5 billion years, but the universe isn't 27 billion light years + 1 grain of sand across, it's 90 billion (plus a grain of sand).

1) I often see this bigger than you expect' figure stated in a 'don't worry about the details as you won't understand them' way, but are you able to explain how this discrepancy is calculated. Is it time dilation as the light travels on its way?

2) If the universe started as a sphere and expanded why isn't it reasonable to imagine space-time as an ever expanding sphere bounded by an  ever weakening front of energy, even if the concept of a 'void' into which it expands is meaningless.

3) I have other questions, but I lack the vocabulary to express them

I'm not entirely certain what you're asking here but for a guess it might equate to why something that sent its light towards us 13.7 million years ago is not 13.7 million light years away but far more than that. The reason is not even slightly difficult to understand, honestly. Viz...

I have been walking north from Trafalgar square for 10 days when I decide to tell you (who live in Trafalgar Square) how far I've got. I've made 20 miles a day, so I'm 200 miles away. The fastest means of communication I have available is horse messenger, capable of covering 50 miles per day. From my point 200 miles away I send a horse messenger to you saying I'm 200 miles away and you receive this message 4 days later. So, when you receive this message, am I 200 miles away? No! Because after I sent the message I carried on walking and in the 4 days it took the horse messenger to get to you I had moved a further 80 miles, so I'm 280 miles away. 

Now suppose I get fitter during the walk. I make 22 miles a day. Then 24 miles a day. Then 28 miles a day. Each time I send you a horse message the horse (who doesn't get any fitter because the Speed Of Horse is a constant in physics  ) builds in a delay which increases relative to my progress.

I am the expansion of the universe and the speed of horse is the speed of light.

Olly

[Floater]

Got to love this forum.

Respect to all out there.

Gareth has said it all.

Excellent analogy/example/explanation, Olly.

Rock on, you guys, I'm just gonna hang on when I can and enjoy the ride ...

[Stub Mandrel]

I'm not entirely certain what you're asking here but for a guess it might equate to why something that sent its light towards us 13.7 million years ago is not 13.7 million light years away but far more than that. The reason is not even slightly difficult to understand, honestly. Viz...

I have been walking north from Trafalgar square for 10 days when I decide to tell you (who live in Trafalgar Square) how far I've got. I've made 20 miles a day, so I'm 200 miles away. The fastest means of communication I have available is horse messenger, capable of covering 50 miles per day. From my point 200 miles away I send a horse messenger to you saying I'm 200 miles away and you receive this message 4 days later. So, when you receive this message, am I 200 miles away? No! Because after I sent the message I carried on walking and in the 4 days it took the horse messenger to get to you I had moved a further 80 miles, so I'm 280 miles away. 

Now suppose I get fitter during the walk. I make 22 miles a day. Then 24 miles a day. Then 28 miles a day. Each time I send you a horse message the horse (who doesn't get any fitter because the Speed Of Horse is a constant in physics  ) builds in a delay which increases relative to my progress.

I am the expansion of the universe and the speed of horse is the speed of light.

Olly

But like you and the horse, the expansion is slower than the speed of light.

Even if they were equal the distance could never be more than TWICE what it was at the time the message was sent.

We and the 'distant source' can't be moving apart faster than the speed of light (a) because that's impossible and ( if we were the light would never have reached us...

For the distance to be double the  original 13.5 billion light years at the time the light arrives we need to be travelling apart at half the speed of light. If that was the case the light from those distant stars would be red-shifted to twice their original wavelength. Is this the case, are we really moving apart that fast?

[Stub Mandrel]

There is no centre- spacetime appears to be expanding everywhere. in other words, every part of it (on a macro scale) is expanding away from all other parts.

As for the point that the Universe "must have a central point"- why does it? The Universe is under no obligation to act as we expect it to. :-)

My pointy is that a universe with a centre is indistinguishable from one without a centre.

Again, it is thought that there is no edge. An edge would imply that there is something beyond it, which most models suggest that there isn't. Then again, there may be multiverses!

I think this is a philosophical question, not a physical one. There are limits to what I have thought of, these limits continually expand with my growing experience of the world but the experinces I haven't had yet don't exist and aren't out there waiting to have light shone upon them.

As far as anywhere more than 53.8 light-years from earth is concerned, I don't exist. The universe with me in it is continually expanding. The alien in his light-ship who left earth with news of my impending birth sees a void without me in it ahead, and looks back to see the same view of the nursing home with me about to appear, frozen in time.

The stubiverse has a conceptual edge, or at least an ever expanding limit, but as fast as my alien messenger is concerned, riding just outside it it doesn't exist... yet.

The concept of being stationary doesn't exist in spacetime. It is a Newtonian construct, along with a universal time which has been superseded with the idea of relative spacetime. Your movement and perception f the passage of time is only realtive to your frame of reference. observers in other frames of reference (ie inside a gravity well or moving at a different speed relative to your frame of reference) will perceive your time and location differently to how you do.

I really, really do get this. I was trying to show that even if you COULD stand still by setting you frame of reference to the centre of the universe you wouldn't be able to tell.

It's actually expanding faster than the speed of light, which explains why there are parts of spacetime that we can never see. They are receding from us so fast that the light from them is red-shifted to infinity. This expansion does not contradict Relativity as Relativity does not forbid sapcetime from expanding faster than c

That's something I have not come across before - see my response to Oli below. But I thought this expansion only took place during the inflationary phase (hence my extra 'grain of sand').

1) Time dialtion (and length contraction and mass increase) is governed by the percentage of the speed of light the object is moving at relative to your frame of reference, as well as the size of the gravity well that it is in.

2) Spacetime doesn't have to be a sphere. http://www.universetoday.com/120157/what-shape-is-the-universe/  https://en.wikipedia.org/wiki/Shape_of_the_universe

3) I have a headache now!

Sorry if all this seems to be pretentious codswallop. I really try to get my head around these things and the sugar coated versions in most books and even Wiklipedia really don't help.

[ollypenrice]

But like you and the horse, the expansion is slower than the speed of light.

Even if they were equal the distance could never be more than TWICE what it was at the time the message was sent.

We and the 'distant source' can't be moving apart faster than the speed of light (a) because that's impossible and ( if we were the light would never have reached us...

For the distance to be double the  original 13.5 billion light years at the time the light arrives we need to be travelling apart at half the speed of light. If that was the case the light from those distant stars would be red-shifted to twice their original wavelength. Is this the case, are we really moving apart that fast?

No, it is perfectly possible. The recession between two bodies due to the expansion of the universe is not governed by the speed of light. The bodies are not racing apart because they are 'moving' in the normal sense but because the space between them is expanding. This is a crucial distinction.

And, yes, you are right. There comes a point at a far enough distance from us at which the expansion of the universe generates a recession which exceeds the speed of light and information from beyond this point will never reach us. The region before this point is known as 'The observable universe' because it is, in principle, observable. Light from this point will one day reach us. But light from beyond this point will never reach us so this part of the universe is, in current understanding, never to be observed.

Edit. And so to your later post...

There is no centre- spacetime appears to be expanding everywhere. in other words, every part of it (on a macro scale) is expanding away from all other parts.

As for the point that the Universe "must have a central point"- why does it? The Universe is under no obligation to act as we expect it to. :-)

 

My pointy is that a universe with a centre is indistinguishable from one without a centre.

I think it would be very easy to distinguish between the two. If you were prepared to believe that we just happened to be at the centre of the universe then Hubble's observations of the linear relationship between distance and recession velocity could just about be accepted without the need for an expanding universe. But hardly. If we were at the centre why would the relationship be linear?

Or you could take the cosmic microwave background, which ought to show a preferential proximity with regard any movement we happen to have.

If you are prepared to ignore the Copernican principle (distrust any conclusion arising out of your occupying some preferential vantage point) then you might find it impossible to distinguish between a universe with a centre and one without. The elegance of the expanding universe hypothiesis is that it predicts or requuires Hubble's law to apply. ANything else requires a lot of fancy dancing and the unlikely belief that the Milky Way, a humdrum spiral galaxy (10^11 galaxies, more or less, in the observable universe) happens to be at the centre. Hum, and I'm the King of Siam! 

Olly

[Zakalwe]

We and the 'distant source' can't be moving apart faster than the speed of light (a) because that's impossible and ( if we were the light would never have reached us...

As Olly said, according to Relativity it's perfectly possible. What is impossible (again according to General Relativity) is to accelerate matter to the speed of light. That would take infinite energy, and the object being accelerated would shrink to zero size in length and increase it's mass to infinity.

Spacetime itself is expanding and the speed of it's expansion can (indeed, is) exceed the speed of light. Special Relativity forbids objects moving away from each other's inertial frame of reference at speeds >c, but in General Relativity there is no inertial frame of reference. As nothing exists "outside" the universe, there is nothing to compare the speed of it's expansion, therefore it can expand faster than c

[ollypenrice]

As Olly said, according to Relativity it's perfectly possible. What is impossible (again according to General Relativity) is to accelerate matter to the speed of light. That would take infinite energy, and the object being accelerated would shrink to zero size in length and increase it's mass to infinity.

Spacetime itself is expanding and the speed of it's expansion can (indeed, is) exceed the speed of light. Special Relativity forbids objects moving away from each other's inertial frame of reference at speeds >c, but in General Relativity there is no inertial frame of reference. As nothing exists "outside" the universe, there is nothing to compare the speed of it's expansion, therefore it can expand faster than c

Yes. The curious thing, if I have this right (I'm an amateur) is that, although the expansion of the universe seems to be accelerating, this does not involve the matter within it (say galaxies) to be accelerating. We perceive oursleves, at first glance, to be unaccelerated in the middle of a universal expansion. We see all the other galaxies as being accelerated. But here's the rub: they all feel the same way. They all see the other galaxies racing away from them. Can we all be right? Sure, if we believe in the expanding universe.

Olly

[Gutross]

I'm confused :s

Your planning on mapping the stars from a singular point in space (I've got this much)

So your planning on mapping from a singular point in time? (Where you lost me)

The reason I asked why is as a lot of objects in space are in orbit or moving in some direction and to completely remove this would be impossible. See Penrose–Hawking singularity theorem.

When you say acceleration is it that of the earth or of other celestial objects?

What I mean is if you were to map a 2°^2 section of sky, your trying to factor out the acceleration of the earth or the objects being mapped or do you mean the earth's rotation?

If its the earth's acceleration is it the acceleration of the earths orbit of the sun? Or is it the sun's orbit of the milky way? Perhaps both maybe you even want to factor in for the earth being pulled ever closer to the sun? Perhaps the milkyway's acceleration towards Andromeda? Or the milkyways movement in space? The ever expanding universe from the big bang? It's just a whole mess of singularity theorem. Which is always changing as not even the worlds finest minds can figure that out, from einstein to hawking.

For example the earth's travelling at 30km/s around the sun, the sun's travelling at 200km/s around the galaxy and that's speed NOT acceleration. Acceleration as such isn't really what's important but rather centripetal acceleration which is the speed of an object to maintain a circular orbit. With this we can factor out the movement with our galaxy but that's it. To go further you'd have to explore the other galaxy's in relation to our own. Knowledge I don't have and you'll need a heavy understanding of physics to do so, if its even obtainable information.

As you can see its a very complex/ impossible calculation depending on what your trying to acheive. I can't quite be bothered to do the math right now but the your going to need to have something to factor it against. I'm not even sure if this is known for any objects out side of the galaxy.

Bottom line is from theoretical point of view its very difficult to do. If your absolutely sure you want to do it go for it. I'd love to see the results you'll probably gain a physics degree and masters and doctorate in the process

However to change the subject from theoretical physics to a more common sense approach. Back to the singular point in space idea such as that if you were to hop on a shuttle, don a spacesuit jump outside and stay right there. Take some pictures in every direction/axis then yes its possible. Just been done already check out any star map all these factor the rotation of the earth.

Then again I could just be completely wrong about what you want to do in which case none of this was relevant at all

in my current state,   mind blown will have to re read later when im fully awake

[Stub Mandrel]

https://en.wikipedia.org/wiki/Metric_expansion_of_space

Has helped.

To sum up - the universe is infinite and has no meaningful 'size' and concepts of the universe being 'the size of a grain of sand' at the end of inflation is lazy shorthand for  'the size of the observable universe' and '300 billion galaxies 'for '300 billion galaxies in the observable universe'.

The 'big bang' did not occur at a point - everywhere sprang into existence and since then the distances between each bit of everywhere have gotten bigger.

We can see a bit of everywhere with the furthest points showing as they were ~13.5 billion years years ago, but most/all of these places are now further away and their later history will never be observable to us.

-ish.

Neil

[Zakalwe]

Here's a good site for you Neill:

http://www.talkorigins.org/faqs/astronomy/bigbang.html