Velocity of our Solar System

[reverend]

Anyone know of anybody having calculated, or attempted to calculate the velocity of our sun with reference to the center of the galaxy, and further, any figures on the velocity of our galaxy with reference to the center of the universe?

 

[Urwumpe]

Inside the galaxy the velocity is known (220 km/s), but it is impossible to calculate the velocity of the solar system relative to the center of the universe - because of relativity, we are always our own center of the universe.

 

[Scarecrow]

Inside the galaxy the velocity is known (220 km/s), but it is impossible to calculate the velocity of the solar system relative to the center of the universe - because of relativity, we are always our own center of the universe.

However, it would be theoretically possible to calculate the position at which the big bang took place, and then find our velocity relative to that place. I don't know any numbers though.

 

[Urwumpe]

However, it would be theoretically possible to calculate the position at which the big bang took place, and then find our velocity relative to that place. I don't know any numbers though.

Would also be impossible. Space expands at least nearly equally in all dimensions (if there would be a difference, that would be interesting for scientists) - also the event horizon of an observer would make it hard to see any other boundary to use as reference. It looks like the universe expands away from us - but of course, it would look the same a few million parsec away.

 

[Scarecrow]

Would also be impossible. Space expands at least nearly equally in all dimensions (if there would be a difference, that would be interesting for scientists) - also the event horizon of an observer would make it hard to see any other boundary to use as reference. It looks like the universe expands away from us - but of course, it would look the same a few million parsec away.

Try a thought experiment: You are Superman (so you can't get hurt), and you are buried in some random place in a huge pile of rocks, and in the exact center of this pile is a ton of high explosives. You are blindfolded. Then the explosives are set off, and the pile, including you, is blown everywhere. You are now someplace in the debris field, and you don't know where you are, but you want to know where the epicenter of the blast was. So you take off your blindfold and stand up. There are no marks on the ground, like craters, so all you have to go on is the debris field. For some reason, you have a pencil and some paper, so you write down all the positions of the debris relative to you, and then take a weighted average. Voila! You now have a pretty good idea of where the explosives were!

As far as I can tell, there's nothing to stop us from doing much the same thing with the universe. Obviously it wouldn't be quite like this, and the math would be more intense, but it's a similar concept.

 

[Urwumpe]

That's not the same as the universe expanding. if it would be as simple, you could look for differences in the relative velocity of galaxies and notice that velocity increases with distance. Also all accelerate away from you. So you conclude, you are the center of the explosion.

In the universe, the problem would be: In any place you observe, regardless how far you go away from Earth, the observation will not change. It is not expanding mass, but expanding space.

 

[Scarecrow]

That's not the same as the universe expanding. if it would be as simple, you could look for differences in the relative velocity of galaxies and notice that velocity increases with distance. Also all accelerate away from you. So you conclude, you are the center of the explosion.

In the universe, the problem would be: In any place you observe, regardless how far you go away from Earth, the observation will not change. It is not expanding mass, but expanding space.

If I was expelled from the Big Bang faster than any other bit of matter, then at this point, I could say "because I see nothing in this direction, and everything in that direction, the Big Bang happened over there." And if I was expelled slower than any other bit of matter, then I could say "because I see equal amounts of matter in all directions, I must be really really close to where the Big Bang happened." As it is, we should be able to say "because we see more stuff in this direction than in that direction, the Big Bang must have happened over there."

Right?

 

[simonpro]

Trying to find where the big bang happened is like doubling the radius of a circle and then asking what corner of the circle has the extra circumference.
It just doesn't make sense. The big bang didn't happen anywhere, it happened everywhere.

 

[pete.dakota]

If I was expelled from the Big Bang faster than any other bit of matter, then at this point, I could say "because I see nothing in this direction, and everything in that direction, the Big Bang happened over there." And if I was expelled slower than any other bit of matter, then I could say "because I see equal amounts of matter in all directions, I must be really really close to where the Big Bang happened." As it is, we should be able to say "because we see more stuff in this direction than in that direction, the Big Bang must have happened over there."

Right?

We can only "see" the waves that have travelled for long to enough to reach the Earth. So we are not looking out into the Universe as it actually IS "now". This means that any given point in the Universe has it's own "Observable" Universe, as it has taken different amounts of time for different wave sources to be seen at that point. It's in keeping with most credited current theories that the boundary of our visible Universe is not the actual "Physical" one.

With no one ever being able to prove the true size or age of the physical Universe, one will never know where the big bang occurred.

 

[ijuin]

If I was expelled from the Big Bang faster than any other bit of matter, then at this point, I could say "because I see nothing in this direction, and everything in that direction, the Big Bang happened over there." And if I was expelled slower than any other bit of matter, then I could say "because I see equal amounts of matter in all directions, I must be really really close to where the Big Bang happened." As it is, we should be able to say "because we see more stuff in this direction than in that direction, the Big Bang must have happened over there."

The problem here is that the Universe as a whole is larger than what we can see--there is an unknown amount of it beyond our cosmic horizon, so far away from us that the light from there has not had time to reach us in the age of the universe. Imagine if you could only see for twenty meters around you when looking at your explosion's debris field, and further imagine that your feet are rooted in place (as we are limited to Earth and will never overtake our cosmic horizon unless we learn to travel faster than light). Now, how can you study the entire explosion? You can't!

A better analogy for cosmic expansion would be the balloon analogy. Draw a number of spots on a balloon, and then inflate it. The spots will spread apart as the balloon expands. Now imagine our universe as a four-dimensional surface expanding in the fifth dimension (or even more dimensions--string theory suggests there are ten). Where is the "center" of the balloon? It's not on any part of the surface!

Anyway, the one thing that we CAN measure our galaxy's motion relative to is the cosmic background radiation. Earth is moving at around 750 km/s relative to this background (though I don't recall which direction).

 

[lalbanof]

If I may put my two cents.

The Big Bang Theory, which says that the Universe started as a very small volume, even a singularity of zero volume, means that this small area, this center of the explosion, comprised everything there is. The Universe itself expanded and so, the Big Bang happened literally everywhere. So, background radiation from the Big Bang comes from everywhere.

Furthermore: Einstein, Cartan, Minkowsky, Poincare and others, based on the fact that light has a constant, finite speed, literally adapted a new geometry for space and time. This means that you cannot regard the Universe in the terms you would regard a city square. There, something happens and you see it almost instantly, the distance being small enough and light being fast.

In the Universe, only those events that are causally connected to you are visible. This means that you are not looking at some kind of "simultaneous" events sphere.

Superman might move faster than the debris, and be able to look at debris close and far. But we are just part of a piece of debris, and are always blindfolded. We can only sense the noise they make, and this noise does not travel faster than the shock wave we ride. In this sense farther noises will be earlier noises.

 

[Linguofreak]

Anyway, the one thing that we CAN measure our galaxy's motion relative to is the cosmic background radiation. Earth is moving at around 750 km/s relative to this background (though I don't recall which direction).

I thought it was 300 km/s, but whatever that velocity is, our velocity relative to the CMB is about the closest we can get to "velocity relative to the 'center' of the universe."

 

[bujin]

Try a thought experiment: You are Superman (so you can't get hurt), and you are buried in some random place in a huge pile of rocks, and in the exact center of this pile is a ton of high explosives. You are blindfolded. Then the explosives are set off, and the pile, including you, is blown everywhere. You are now someplace in the debris field, and you don't know where you are, but you want to know where the epicenter of the blast was. So you take off your blindfold and stand up. There are no marks on the ground, like craters, so all you have to go on is the debris field. For some reason, you have a pencil and some paper, so you write down all the positions of the debris relative to you, and then take a weighted average. Voila! You now have a pretty good idea of where the explosives were!

As far as I can tell, there's nothing to stop us from doing much the same thing with the universe. Obviously it wouldn't be quite like this, and the math would be more intense, but it's a similar concept.

The "Big Bang" is a bit of a misnomer. It wasn't an explosion in space. It was an expansion of space. Your analogy with the rocks and explosives is not representative of the Big Bang event.

 

[JamesG]

"The Big Inflate" doesn't have as catchy a ring to it.

I like the analogy of a sponge the best. If you take a dry sponge and squeeze it down into as tight as ball as possible until most of the air is out and its "solid", that is the notional start point and your little ball of sponge is the entire universe. When you let it go, it expands in all directions and the spaces within are analagous to the voids between galaxies and stars.

 

[Loru]

For making it simple enough to understand:

Picture a typical birthday baloon and mark it with dots. Then inflate the baloon more and more - every dot is runnig away from eachother. Every dot has its own point of view and every dot see that all others are escaping from it. Just like galaxies in expanding universe.

And now for the center of the universe and back to baloon analogy:
Surface of the baloon is actualy space (it has 2 dimension instead of real 3 dimensional space). Try to find center point on this expanding surface. Like real space it has no boundaries and no center at all but it have finite volume.

Like Earth's surface - you can travel around the world in all directions but there are no boundaries that stops you going anywhere on the surface. There is no "end of the world" place where you can't go further and there is no center of the surface of Earth. But still surface has finite area (for Earth it's about 510 072 000 km², for baloon it's few hundred square centimiters).

Now most challanging:
Add to the surface of baloon another dimension and you have three dimensional and expanding space. It's difficult to imagine but that how it's described by all relativistic models of space.

Geometry of space isn't flat as we can experience on earth but it's curved. We can barely imagine that but we're living in three dimensional world and to picture curvature of space itself you need to use non-Euclide geometry. You need to think in four dimensions and this is quite strange.

Sum: There is no center of the Universe and boundaries of it.

see also for details:
Special and General Theory of Relativity
Differential geometry


PS: I omitted time and wrote only about space to avoid any further misunderstandings.

 

[atuhalpa]

Is space expanding or is matter contracting?

I have a question. This concept has been in my mind for awhile but I have never queried anyone about it. As I realize the brainpower in this forum is quite impressive I ask this: Is there mathematically any difference or way to differentiate between space EXPANDING or.........matter CONTRACTING? In my limited understanding of relativity I see no difference.

 

[Artlav]

I have a question. This concept has been in my mind for awhile but I have never queried anyone about it. As I realize the brainpower in this forum is quite impressive I ask this: Is there mathematically any difference or way to differentiate between space EXPANDING or.........matter CONTRACTING? In my limited understanding of relativity I see no difference.

The theory fits both expansion and contraction.

The case of contraction implies that time flows backwards, and what we see as future is actually a kind of explosion played backwards, with the Universe getting into a small and complex something at the Big Unbang end. Red shift accounted as light infall making it appear redder, galaxies have their form as spirals winding backwards.

The case of expansion implies time flowing conventionally, usual causality, something complex in the past and a diffuse nothing in the future. Red shift as light loosing energy being stretched, dark matter to make galaxies, dark energy to account for expansion rate inconsistencies.

Both interpretations are possible, but people tend to find expansion more credible.

 

[Loru]

I understand atuhalpa's question quite different than you Artlav.

I think he meant that space expansion can be the same as matter contraction (eg. all of atoms & molecues and all macro-objects are getting smaller). Optically with one eye and perfect viewing condition you can't see difference between contracting object and object that is moving away from you. Like the analogy between gravity and acceleration.

And I will have to ask my friend (Astrophysicist) for it.

Anyway Artlav's explanation is correct. Read about closed Friedmann universe and Big Crunch.

Edit: I found the answer.

There will be the same thing (space expanding & matter contracting) only when all other forces, universe constants will be scaled down also. In other case that will not work. Atoms will fall apart or matter will colapse into black holes.

 

[tori]

There will be the same thing (space expanding & matter contracting) only when all other forces, universe constants will be scaled down also. In other case that will not work. Atoms will fall apart or matter will colapse into black holes.

Correct. I believe the most obvious manifestation would be the apparent elongation of EM wavelengths, although that would depend on the rate at which the contraction takes place.

 

[flaugher]

Velocity of Solar System

Good grief! This thread was started in '08, and now you guys have picked it up again. I love this forum. How about back to the original question. Try this solution. Is our solar system actually orbiting the center of the galaxy, OR are we just traveling along with our nearest spiral arm, OR could we be traveling along with our nearest spiral arm AND oscillating back and forth across the center line of the arm (Normal Arm, I think). The reason I ask the question is this: What if we ARE oscillating back and forth across the arm and we are presently located at or near the extent of our travel, the point where we turn around and head back in toward the center line after making a pass through the middle some millions of years ago. If so, could we be totally messing ourselves altogether up by looking at and making assumptions of red-shift and blue-shift? Anybody ever rode a "scrambler" at the county fair? Who's coming toward you and who's moving away?