If the galaxy is spinning, how come centrifigul force doesn't cause the planets and everything to move outwards?

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If the galaxy is spinning, how come centrifigul force doesn't cause the planets and everything to move outwards?

Post by glassynails » Wed Aug 31, 2016 5:51 pm

Ok, our galaxy spins. How come centrifugal force doesn't rip our galaxy apart and cause all of it's contents to move outwards to the edges of the galaxy?
Do you think gravity might be a result of something to do with the spin of the galaxy? I would guess that gravity also exists outside of our galaxy though.
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Re: If the galaxy is spinning, how come centrifigul force doesn't cause the planets and everything to move outwards?

Post by astro64 » Wed Aug 31, 2016 6:38 pm

Because of gravity. And gravity is caused by mass, not by spin.

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Re: If the galaxy is spinning, how come centrifigul force doesn't cause the planets and everything to move outwards?

Post by Andrew Pohlman » Wed Aug 31, 2016 7:00 pm

Ahem - we are moving out - and at an ever increasing rate! Gravity holds us more or less together or slows down the outward separation.

Nobody knows what gravity is. There has been a proposed particle of gravity called a "graviton". People can measure the effects of gravity and it's frequency (it creates waves). String theorists think it is a tiny little dimension that only has an affect in very large masses like planets. But nobody really knows what gravity is. We only know what it does from observation.
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Re: If the galaxy is spinning, how come centrifigul force doesn't cause the planets and everything to move outwards?

Post by chiral3 » Wed Aug 31, 2016 7:05 pm

astro64 wrote:Because of gravity. And gravity is caused by mass, not by spin.
Good pun. Some would argue if it was spin 2 we would have seen it already!
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Re: If the galaxy is spinning, how come centrifigul force doesn't cause the planets and everything to move outwards?

Post by astro64 » Wed Aug 31, 2016 7:43 pm

Andrew Pohlman wrote:Ahem - we are moving out - and at an ever increasing rate! Gravity holds us more or less together or slows down the outward separation.

Nobody knows what gravity is. There has been a proposed particle of gravity called a "graviton". People can measure the effects of gravity and it's frequency (it creates waves). String theorists think it is a tiny little dimension that only has an affect in very large masses like planets. But nobody really knows what gravity is. We only know what it does from observation.
We are not moving out in our own Galaxy. Gravity is locally strong enough to bind the galaxy. The Universe is expanding, in the form of increasing distances between distant galaxies, but not the space inside galaxies.

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Re: If the galaxy is spinning, how come centrifigul force doesn't cause the planets and everything to move outwards?

Post by singularity » Wed Aug 31, 2016 8:15 pm

I think we should leave this dark matter to experts. Pun intended :wink:

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Re: If the galaxy is spinning, how come centrifigul force doesn't cause the planets and everything to move outwards?

Post by singularity » Wed Aug 31, 2016 8:19 pm

Also, that's what you get when you're WIMP :shock: you hold the whole galaxy together. Pun... aahh schneikels...

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Re: If the galaxy is spinning, how come centrifigul force doesn't cause the planets and everything to move outwards?

Post by glassynails » Wed Aug 31, 2016 8:27 pm

Right, I've always wondered what causes gravity itself. We know that something falls towards earth, that's observable, but we don't know "why" it falls. What actually is pulling the object towards Earth? That's what I've always wanted to know.

So back to the question. It's gravity that keeping the planets from spinning outward in the spinning galaxy?
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Re: If the galaxy is spinning, how come centrifigul force doesn't cause the planets and everything to move outwards?

Post by tyke » Wed Aug 31, 2016 9:19 pm

It's all held together by strings...


... at least in theory.

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Re: If the galaxy is spinning, how come centrifigul force doesn't cause the planets and everything to move outwards?

Post by Stephen Kenyon » Wed Aug 31, 2016 9:24 pm

glassynails wrote:Right, I've always wondered what causes gravity itself. We know that something falls towards earth, that's observable, but we don't know "why" it falls. What actually is pulling the object towards Earth? That's what I've always wanted to know.

So back to the question. It's gravity that keeping the planets from spinning outward in the spinning galaxy?
Everything exerts a gravitational pull on everything else, and the stars in a galaxy attract each other enough that the galaxy stays together even though it is spinning round.
Dark matter was mentioned as well, which as I understand it, is what is needed to explain the fact that galaxies hold together even though observationally there isn't enough matter there for them to do so.
But gravity is only a theory, so maybe its not really there at all. OK, we won't go there. But look up Tim Minchin's pithy comment if you don't mind sweariness.
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Re: If the galaxy is spinning, how come centrifigul force doesn't cause the planets and everything to move outwards?

Post by powderedtoastman » Thu Sep 01, 2016 6:54 am

glassynails wrote:Right, I've always wondered what causes gravity itself. We know that something falls towards earth, that's observable, but we don't know "why" it falls. What actually is pulling the object towards Earth? That's what I've always wanted to know.

So back to the question. It's gravity that keeping the planets from spinning outward in the spinning galaxy?
One theory (in fact that of Einstein, I believe!) is that the force of gravity is due to disturbances in space-time caused by mass.. there is a visualization where a massive object like the sun creates a sort of "well in spacetime" where un-perturbed spacetime would be a flat plane. So the objects sort of fall to the center of that well.
Interestingly, this theory predicts gravitational lensing should happen (light literally being bent by massive objects!) which has indeed been observed.
But of course it still doesn't exactly answer "why."

As for gravity and the galaxy, the stars in the galaxy could possibly be thought to be orbiting around the massive core similar to how the planets orbit around stars The force of gravity is what causes the orbit to work in the first place.
A very big problem with this: in many galaxies, the outer stars are found to revolve around the center at the same *angular* rate as those closer to the center, which cannot be accounted for by classical dynamics. Planets, on the other hand, have a much lower angular rate further from the star/sun, which is what we expect as the force of gravity falls off as 1/distance-squared and the circumference of the orbit is proportional to the distance.
That observation of stars orbiting is one of the reasons dark matter is theorized.. otherwise some sort of adjustment to classical dynamics would be needed to explain this phenomenon (in fact somebody did come up with something called Modified Newtonian Dynamics or MOND, which does mathematically fit the effect, but there may not be a real basis to believe it).

You ask a lot of deep questions, maybe you should go back to school and study physics and/or philosophy!

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Re: If the galaxy is spinning, how come centrifigul force doesn't cause the planets and everything to move outwards?

Post by rojarosguitar » Thu Sep 01, 2016 7:12 am

Maybe a simple answer is that if it wasn't for the rotational movement around the center of gravity (I would reserve spinning for eigen-rotation) everything would fall into the central mass, so the rotation actually ensures (or is a condition for) that the galaxy doesn't collapse.
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Re: If the galaxy is spinning, how come centrifigul force doesn't cause the planets and everything to move outwards?

Post by petermc61 » Thu Sep 01, 2016 8:46 am

Pffffftt.

The universe is flat.

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Re: If the galaxy is spinning, how come centrifigul force doesn't cause the planets and everything to move outwards?

Post by PeteJ » Thu Sep 01, 2016 11:43 am

powderedtoastman wrote:One theory (in fact that of Einstein, I believe!) is that the force of gravity is due ....
Thanks powdertoastman. Nice post.

I spent some happy time on a science forum once arguing that gravity is a repulsive force. I was shouted at by a few people, but then someone came along and pointed out that that a French physicists published a repulsive theory of gravity, er, no, a theory of repulsive gravity, in the early 20th century, and it works. You just have to turn everything on its head. Many scientific theories have this property of still working when they are turned on their head.

I'm no physicist but to me a repulsive gravity works better. I've wondered if it might give us a different angle on dark matter.

My problem with the idea of mass curving space is that it seems requires an interaction between mass and space, and thus a carrier of that interaction. Iow, we might need gravity to explain how mass curves space, which is not progress. But no doubt I'm muddled.

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Re: If the galaxy is spinning, how come centrifigul force doesn't cause the planets and everything to move outwards?

Post by astro64 » Thu Sep 01, 2016 1:10 pm

PeteJ wrote:
powderedtoastman wrote:One theory (in fact that of Einstein, I believe!) is that the force of gravity is due ....
Thanks powdertoastman. Nice post.

I spent some happy time on a science forum once arguing that gravity is a repulsive force. I was shouted at by a few people, but then someone came along and pointed out that that a French physicists published a repulsive theory of gravity, er, no, a theory of repulsive gravity, in the early 20th century, and it works. You just have to turn everything on its head. Many scientific theories have this property of still working when they are turned on their head.

I'm no physicist but to me a repulsive gravity works better. I've wondered if it might give us a different angle on dark matter.

My problem with the idea of mass curving space is that it seems requires an interaction between mass and space, and thus a carrier of that interaction. Iow, we might need gravity to explain how mass curves space, which is not progress. But no doubt I'm muddled.
One example of the progress Einstein's concepts of mass and gravity and space-time provide is that they properly accounts for e.g. bending of light in gravitational fields (extensively observed, look for "gravitational lensing") and the change in the rate at which time passes in gravitational fields (also observed and used as I mentioned previously in your GPS system). Newtonian physics doesn't get this right. General relativity also encompasses the correct mathematical description of the expanding universe.

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