Almost a straight line

[kaneda]

It is said that dark matter is needed to hold the galaxy together, otherwise stars would just fly off out of the galaxy at the speeds they travel. Our sun moves at about 175 mps, almost stationary by galactic standards.

 

The ancients thought the Earth was flat. If you look at any circle close enough, a small enough piece of it will look straight. An arc second is just 102 feet at the equator. The Sun/Earth take 200,000,000 years to travel once around the galaxy, some 188,400 light years. An arc second of that is over 847 billion miles and it takes the Sun/Earth over 153 years to travel that distance, for the equivalent curvature over a distance of 102 feet on Earth.

 

It could be thought by a casual observer that our solar system is travelling in a perfectly straight line because it is only when measured incredible accurately or over a long period of time that any curvature is noticed. I think this curvature is so casual (probably the original motion) that unless a strong gravitational force acts on our solar system, it will continue forever to travel it as though travelling in a straight line.

[Realitycheck]

Moves at 175 mps compared to what? Maybe the galaxy that we are in is moving at 10,000 mps, relative to the universe. I can see where we are somewhat locked into an orbit around the milky way, but compared to the universe, the implications expand.

[swansont]

I think the issue is that, for a circular orbit, a = v^2/r and the acceleration is a = GM/r^2. You don't have to measure the arc.

 

If we just happen to be in a spiral configuration, and we are all traveling at some velocity, the question becomes: how did this structure come to be?

[kaneda]

agentchange. As you say, 175 mps around the galaxy's centre. Our sun is heading towards Vega so not a mathematical perfect orbit.

 

swansont. If you bend space (due to a gravitational source), you can bend the path of light travelling through it. Since light is waves, this would suggest that space has structure. Possibly when the universe was created, there were swirls and eddies like you get in water and that is where matter congregated? We know that in space once motion starts, it continues until acted on by an outside force.

[swansont]

swansont. If you bend space (due to a gravitational source), you can bend the path of light travelling through it. Since light is waves, this would suggest that space has structure. Possibly when the universe was created, there were swirls and eddies like you get in water and that is where matter congregated? We know that in space once motion starts, it continues until acted on by an outside force.

 

A) yes

B) I don't see how that follows. Geometry does not necessarily imply structure.

C) possibly, yes, I suppose, but why postulate that? What would cause it?

[kaneda]

swansont. B) How would light waves bend unless there is something to make them bend?

 

C) If space has structure, then the violence of creation and expansion may have caused it to do so unevenly.

[swansont]

swansont. B) How would light waves bend unless there is something to make them bend?

 

Because it's not flat. The null geodesic (what seems to be a straight line) is a curve.

[Realitycheck]

Our sun moves at about 175 mps, almost stationary by galactic standards.

 

It says here that the sun travels around the Milky Way at 225,000 mps.

 

The Sun moves around the Milky Way at 225 kilometers per second.

 

http://map.gsfc.nasa.gov/universe/uni_matter.html

 

 

Lots of good, easy-to-read, up-to-date information on this site, of which I am just now getting caught up on.

[kaneda]

swansont. Light travels in a straight line unless something causes it to change direction. It can only do that in space if space is bent/curved.

 

agentchange. 175 miles per second. I didn't go to school within the last decade or so, so normally don't talk metric.

 

I checked up and see from the figure I originally had, estimates have changed from 225 to 250,000,000 years for one orbit with correspondingly different speeds. Though these change the figures in my original post, they do not change the basic premise that Earth travels in an almost straight line for a century at a time so hardly a sharp curve which would throw it out of the galaxy.

[swansont]

swansont. Light travels in a straight line unless something causes it to change direction. It can only do that in space if space is bent/curved.

 

Yes. The presence of mass and energy bend space — that's the conclusion of general relativity. Why does this require that space have structure?

[Janus]

swansont.

agentchange. 175 miles per second. I didn't go to school within the last decade or so, so normally don't talk metric.

 

 

I've haven't gone to school within the last 3 decades, but I still use metric when talking science.

[kaneda]

Janus. It took me a while to get to using centigrade though I still see some scientists using fahrenheit. Degrees absolute never really seemed to catch on (or at least as far as I've noticed). Admittedly metric does make it easier to work things out in your head though calculators bypass that.

 

swansont. How do you bend what is just a vacuum and nothing more?

 

When I say space has structure, I mean it is not a vacuum but some kind of material that allows light to travel through it as waves. If on our scale we register it as basically being "nothing" then whatever it is, it is beyond our comprehension.

[swansont]

swansont. How do you bend what is just a vacuum and nothing more?

 

When I say space has structure, I mean it is not a vacuum but some kind of material that allows light to travel through it as waves. If on our scale we register it as basically being "nothing" then whatever it is, it is beyond our comprehension.

 

Are we moving through this structure or are we at rest with respect to it? How can we tell?