Helical model of the solar system

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 broken spectre 05 Jan 2016
Beautiful, unexpected and obvious once you've considered it...

youtube.com/watch?v=0jHsq36_NTU&
 Robert Durran 05 Jan 2016
In reply to broken spectre:

All relative innit.
 john arran 05 Jan 2016
In reply to broken spectre:

Lovely graphics and a cool reminder that the old order is limited.

But... If the rotational model fits there's nothing wrong with maintaining it - just like Newtonian physics tells us almost everything we need to know about how objects behave on a macro scale.
 Jon Stewart 05 Jan 2016
In reply to Robert Durran:

> All relative innit.

zatly. If you're talking about the solar system, then surely the sun's a sensible spot to call the origin, rather than the centre of the milky way - I'm guessing that's what the solar system moves at 70,000km/h relative to?
Lusk 05 Jan 2016
In reply to broken spectre:

Is the planetary plane in that orientation or is it parallel (???) to the direction of the Sun's motion?
 Robert Durran 05 Jan 2016
In reply to Lusk:

> Is the planetary plane in that orientation or is it parallel (???) to the direction of the Sun's motion?

Good question! I bet they just used that orientation to make it look pretty.
 Brass Nipples 05 Jan 2016
In reply to broken spectre:

What useful predictions does it make that the current model doesn't ?

 Robert Durran 05 Jan 2016
In reply to Jon Stewart:

> zatly. If you're talking about the solar system, then surely the sun's a sensible spot to call the origin, rather than the centre of the milky way.

Yes, really about as daft as an animation of traffic in central London in a frame of reference where Big Ben is moving at about 600 odd miles per hour around its line of latitude.
In reply to Lusk:

I would (also) be interested to know this! I have no idea.
 Jon Stewart 05 Jan 2016
In reply to Lusk:

> Is the planetary plane in that orientation or is it parallel (???) to the direction of the Sun's motion?

Good point - but I've not got my head round what the sun's motion is relative to. We're in a rotating frame of reference here in the milky way, is that rotation part of what we're calling "the sun's motion"?
1
 Jon Stewart 05 Jan 2016
In reply to Orgsm:

Apart from it looking spirally, a bit like seashells, none. It's not a different model, it's just arbitrarily choosing a different frame of reference to describe the motion of things.
 wintertree 05 Jan 2016
In reply to broken spectre:

"Dragging the planets in its wake". So wrong it's not even wrong. The whole lot was moving like that when it was a ball of gas, and as it was collapsing down to a solar system, and as it is today.

Nice animation though.
 Brass Nipples 05 Jan 2016
In reply to Jon Stewart:

In which frame of reference does the Sun travel in a straight line?
Lusk 05 Jan 2016
In reply to Robert Durran:

(I think!...) According to the Big Bang Theory, every point is the centre of the universe, every other point is moving away from every other point, think of the surface of an inflating balloon. So, is the Sun actually moving???!!!
In reply to Lusk:

Steady on Lusk, I only recently annulled membership to the Flat Earth Society (apparently it's actually an oblate spheroid!). You're blowing my mind!
 Chris Craggs Global Crag Moderator 05 Jan 2016
In reply to broken spectre:

How do you get a vortex in a vacuum?


Chris
 Jon Stewart 05 Jan 2016
In reply to Orgsm:

> In which frame of reference does the Sun travel in a straight line?

That's the question, isn't it. Stars don't move about much, relative to each other within galaxies, right? All bound together into fairly stable kind of thing...so in a FOR in which you observe the milky way's rotation, the sun's moving in an orbit (so a straight line at the scale of the solar system). So this FOR is the local group? Or can you go bigger than that?

Now I'm really confused because I don't want there to be a universal FOR, but it seems like the big intergalactic structures provide one...and does the milky way rotate relative to this, giving us our "moving through space at 700,000km/hr" figure?
In reply to Chris Craggs:

A vacuum?! The plot thickens... Or thins in this case!
 Robert Durran 05 Jan 2016
In reply to Jon Stewart:

> Good point - but I've not got my head round what the sun's motion is relative to. We're in a rotating frame of reference here in the milky way, is that rotation part of what we're calling "the sun's motion"?

I presume the frame of reference being used is one in which the galactic centre is stationary. In that frame of reference the sun is moving in a vast circle, so vast that over pretty long distances it seems to be moving in a straight line. Of course it is actually accelerating towards the galactic centre. This acceleration is not relative; acceleration is absolute.
 hokkyokusei 05 Jan 2016
In reply to Lusk:

> Is the planetary plane in that orientation or is it parallel (???) to the direction of the Sun's motion?

No.

http://www.slate.com/blogs/bad_astronomy/2013/03/04/vortex_motion_viral_vid...
 Robert Durran 05 Jan 2016
In reply to Jon Stewart:

> Now I'm really confused because I don't want there to be a universal FOR, but it seems like the big intergalactic structures provide one...and does the milky way rotate relative to this, giving us our "moving through space at 700,000km/hr" figure?

I think you may need to read chapter 2 ("The Universe and the Bucket") of Brian Greene's "The Fabric of the Cosmos". I think I need to read it again.............

 Mr Lopez 05 Jan 2016
In reply to Chris Craggs:

> How do you get a vortex in a vacuum?

> Chris

That was my thought too. Though on second thoughts space is not a complete vacuum, but whatever matter is out there would be also moving in the same direction and at the same speed as the rest of the solar system, so no vortexes to be found anywhere.

Nice animation though
 EdH 05 Jan 2016
In reply to Jon Stewart:

The bath of radiation left over from when the universe was small and hot gives a "universal" reference frame. Our speed through this is (comparatively) not too hard to measure.

This is also the frame where the large scale structures in the universe are moving away from each other uniformly in all directions because of space expanding. (That these two frames coincide isn't a coincidence!)

There's no problem with this!
1
 deepsoup 05 Jan 2016
In reply to Lusk:
> every other point is moving away from every other point

Not uniformly. For example 'our' galaxy is on a collision course with Andromeda. Hang on to your hats in about 4 billion years time.
 joe.wahab 06 Jan 2016
In reply to EdH:

I'm reasonably sure the first part of that isn't true. In my understanding one of the postulates of relativity is there is no preferred inertial frame to any other - there is no such thing as a 'universal' reference frame.

Also, to deepsoup, just because we are on a collision course with Andromeda doesn't mean that space isn't expanding uniformly. Have a read about Hubble's Law here: http://hyperphysics.phy-astr.gsu.edu/hbase/astro/hubble.html
 deepsoup 06 Jan 2016
In reply to joe.wahab:
> Also, to deepsoup, just because we are on a collision course with Andromeda doesn't mean that space isn't expanding uniformly.

Oh indeed, but it does mean that not everything is moving away from everything else. Even on quite a big scale. I find the idea of two galaxies bumping into each other quite mind boggling.
 EdH 06 Jan 2016
In reply to joe.wahab:

It is. You need to distinguish between symmetries of the laws of physics, and the symmetries of an actual system.

The former means we're allowed to use the same laws of physics to calculate stuff if we work in a frame where the cmb is moving (or equivalently work in a frame where galaxy clusters in one direction are moving away at a faster speed than those in the opposite direction). But because the universe explicitly breaks lorentz symmetry, it still makes sense to talk about the cmb providing a special frame in which the universe is at rest.
In reply to Chris Craggs:

> How do you get a vortex in a vacuum?

> Chris

I just usually hoover over it a couple of times
Lusk 06 Jan 2016
In reply to deepsoup:

> I find the idea of two galaxies bumping into each other quite mind boggling.

The space between objects is VAST! Take a look at this ... http://apod.nasa.gov/apod/ap151225.html
So, 'they' reckon that galaxies just merge together with very few collisions.
 deepsoup 06 Jan 2016
In reply to Lusk:
> The space between objects is VAST!
Yep, that's a source of much of the boggling. The timescales involved too - there's a similar problem as there is with the spaces, *so* many orders of magnitude bigger than anything you can truly get your head around.

Nice little film, ta for the link. They're definitely cheating when they sketch out the orbit of Neptune and say "and this is the edge of the solar system" though - sorry boys, you'll be needing a bigger patch of desert for that.

Thanks to you I've just been reading about the "Kuiper Cliff" - probably the most productive thing I've done so far today, at least I learned something.

For me I think the thing that best gets across the idea of the scale of the Solar System is the "Pale Blue Dot" photo. https://en.wikipedia.org/wiki/File:Pale_Blue_Dot.png

In reply to Lusk:

Great video, thanks for the link!
 Jon Stewart 06 Jan 2016
In reply to EdH:

> The bath of radiation left over from when the universe was small and hot gives a "universal" reference frame. Our speed through this is (comparatively) not too hard to measure.

> This is also the frame where the large scale structures in the universe are moving away from each other uniformly in all directions because of space expanding. (That these two frames coincide isn't a coincidence!)

> There's no problem with this!

Thanks, that answers my question. There is a universal reference frame then, but within that it's more sensible to use relativity to understand what's going on locally as to do otherwise would likely induce motion sickness.
 EdH 06 Jan 2016
In reply to Jon Stewart:

Incidentally, the way to measure this speed is by looking at the temperature of the sky: doppler shifting means that the background radiation we're moving towards looks hotter than the radiation we're moving away from
http://apod.nasa.gov/apod/ap010128.html
in this picture the red regions are at a temperature of about -270.43 Celsius while the blue are -270.42 Celsicus!
 Jon Stewart 06 Jan 2016
In reply to EdH:

Brilliant, thanks! That answers all my questions very neatly indeed.
 jkarran 06 Jan 2016
In reply to broken spectre:

> I would (also) be interested to know this! I have no idea.

http://curious.astro.cornell.edu/our-solar-system/159-our-solar-system/the-...

The galactic plane is significantly misaligned from the ecliptic.
jk
 Robert Durran 06 Jan 2016
In reply to Lusk:

> The space between objects is VAST! Take a look at this ... http://apod.nasa.gov/apod/ap151225.html

Thanks. That's really good.
 d_b 06 Jan 2016
In reply to broken spectre:

Very pretty animation, but the text is pretty much crackpot woo.

There is nothing particularly special about the fact that the solar system is moving. Relativity lets you pick your own frame of reference after all.

We are traveling at 70,000 km/h relative to the galactic centre, we are also going at the best part of light speed relative to a cosmic ray that just hit our atmosphere, and the best part of light speed in the opposite direction relative to another one.

In reply to davidbeynon:

Thanks David. The more it's analysed, the less sense it all makes (this is probably down to the constraints of my own brain!). I just foolishly googled "what shape is the universe" and the best answer I could find was "Based on the most recent Planck data, released in February 2015, our Universe is most likely… Flat. Infinitely finite, not curved even a little bit, with an exact, critical amount of energy supplied by dark matter and dark energy."

Here lies another can of worms! Infinitely, finite, flat worms squirming around in their own dark matter.

..I'm stepping away from the keyboard now for some cheese on toast and a nap (and vowing to leave cosmology to the experts)!
 d_b 07 Jan 2016
In reply to broken spectre:

Well, if the result of all this is cheese consumption then it's time well spent if you ask me.

Mines the "blue buxton" and a glass of port. Ta.
 humptydumpty 07 Jan 2016
In reply to davidbeynon:

> There is nothing particularly special about the fact that the solar system is moving. Relativity lets you pick your own frame of reference after all.

Can I just pick my frame of reference as Earth, and assume everything else revolves around that? Is it equally correct to a heliocentric FoR?
 d_b 07 Jan 2016
In reply to humptydumpty:

You can in GR, although most people don't because it makes the maths much harder.
 Robert Durran 07 Jan 2016
In reply to humptydumpty:

> Can I just pick my frame of reference as Earth, and assume everything else revolves around that? Is it equally correct to a heliocentric FoR?

You could, but you would then be in an accelerating frame of reference (the earth is accelerating towards the sun), which is unnecessarily messy. Of course the sun is accelerating towards the galactic centre but this acceleration is tiny and can be safely neglected for all practical purposes.
 humptydumpty 07 Jan 2016
In reply to davidbeynon:

Great! Thanks.
 humptydumpty 07 Jan 2016
In reply to Robert Durran:

Hmm not so simple then? Where can I go that's not accelerating?
 d_b 07 Jan 2016
In reply to humptydumpty:

You may not thank me later. By "much harder" I mean that formerly simple calculations become esoteric exercises in masochism.
 Robert Durran 07 Jan 2016
In reply to humptydumpty:

> Hmm not so simple then? Where can I go that's not accelerating?

I presume the galactic centre would be an improvement (though we are accelerating towards Andromeda). And there is the inconvenience of a rather big black hole.....
 d_b 07 Jan 2016
In reply to Robert Durran:
Best bet for low acceleration would be in the middle of an intergalactic void I guess. It would probably take a while to get there though.
Post edited at 16:04

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