# What can be defined as being motionless?

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 1035209.  Wed Nov 13, 2013 9:01 pm Is anything truly motionless. The planet and everything on it is rotating at roughly 1000mph. The planet orbits the sun at 67000 mph, our Milky Way galaxy spins at 515000mph and the galaxy is moving at over 2 million mph. How can anything be defined as motionless?

 1035227.  Thu Nov 14, 2013 3:52 am If there was a big bang*, then theoretically there may be a single 'central' point at which it might be possible for an arbitrarily small particle to remain motionless momentarily Gravity is everywhere, and all particles exert some force on all others, sufficient to induce some motion So while something cannot be motionless, it it can be defined as motionless relative to a given frame of reference * there is now some more doubt being heaped upon this thoery

1035230.  Thu Nov 14, 2013 4:04 am

 chrisboote wrote: If there was a big bang*, then theoretically there may be a single 'central' point at which it might be possible for an arbitrarily small particle to remain motionless momentarily

No, because the big bang created the universe. The point at which the big bang occured was the entire universe and the entire univese is now where the big bang happened. If you want to ask, where "where did the big bang occur?", it happened here and that is true wherever you happen to be.

1035269.  Thu Nov 14, 2013 6:43 am

 AndyMcQueen wrote: How can anything be defined as motionless?

Simple. Einstein's theory of relativity shows that all motion is relative to another object. Motion in and of itself is meaningless.

So all you have to do is define yourself as the centre of a rest frame and, hey presto, you're motionless :)

 1035281.  Thu Nov 14, 2013 8:05 am I used that argument to get out of a speeding ticket. So they gave me a parking ticket instead.

 1035317.  Thu Nov 14, 2013 9:42 am Lovely, DJ!

1035330.  Thu Nov 14, 2013 10:14 am

 chrisboote wrote: ... it it can be defined as motionless relative to a given frame of reference

The most obvious frame of reference for this definition would be that of the cosmic microwave background (CMB) radiation, which coincides with the "Hubble Flow" (the motion of all the galactic velocities, averaged out).

Against the CMB frame, our own Milky Way galaxy is moving in the direction indicated by the constellation Leo.

1035418.  Thu Nov 14, 2013 6:29 pm

 djgordy wrote: I used that argument to get out of a speeding ticket. So they gave me a parking ticket instead.

Funny!

 1035420.  Thu Nov 14, 2013 6:38 pm +1 n1 djg On the OP: Errm - everything is motionless with respect to itself...

1035421.  Thu Nov 14, 2013 6:41 pm

 dr.bob wrote: Einstein's theory of relativity shows that all motion is relative to another object.

You don't need Einstein's Relativity to show that all motion is relative.

1035518.  Fri Nov 15, 2013 7:39 am

 Posital wrote: You don't need Einstein's Relativity to show that all motion is relative.

Yep, think it was some chap called Galileo who originally came up with the concept of relativity. Bright lad. Though I think you do need the constancy of the speed of light (and Einstein's Special Relativity theory) to give solid evidence for the idea. Einstein, after General Relativity had brought in curved space-time, came back to the idea of the ether with a more favourable view.

What I don't understand is how the "quantum foam" of virtual particles popping in & out of existence doesn't provide a reference frame. But apparently, as an object moves, it sees its own quantum foam moving along with it. But I don't understand this. Presumably such a concept would unite Einstein's relativity and quantum theory - but I thought they hadn't done that yet?

1035555.  Fri Nov 15, 2013 9:21 am

gruff5 wrote:
 Posital wrote: You don't need Einstein's Relativity to show that all motion is relative.

Yep, think it was some chap called Galileo who originally came up with the concept of relativity. Bright lad. Though I think you do need the constancy of the speed of light (and Einstein's Special Relativity theory) to give solid evidence for the idea.

Quite so. Galileo showed that motion was relative. Einstein showed that all motion is relative.

 1035639.  Fri Nov 15, 2013 3:03 pm Isn't it obvious that motion is relative without needing to refer to great minds? If you run towards a pig - you're going to catch it quicker if it's walking away than if it's running away. I think I can extended this theory to include all the animals from the Lion King - and hopefully this can even include planets and other stuff at a pinch. There - proof that motion is relative without constant light speed or special relativity. But I'm not expecting a Nobel prize any time soon.

1035862.  Sun Nov 17, 2013 7:14 am

 Posital wrote: Isn't it obvious that motion is relative without needing to refer to great minds?

Well, as Dr Bob pointed out, the notion that all motion is relative is the bit that needs great minds to prove. And Einstein didn't so much prove that a universal reference frame, such as the ether, didn't exist, but that it was unnecessary.

It can be almost impossible to prove that something doesn't exist - ref. the 'does God exist' debate!. By Occam's Razor, the ether was done away with, but Occam's razor is not infallible - our Universe being the ultimate example of this: "Why is there something, rather than nothing?"

Another great mind, Isaac Newton, tended more to the idea that space was a stage or background upon which events took place - ie he was more of a non-relativist. His notion, known as "Newton's Bucket" demonstrates that there is absolute rotational motion, seemingly relative to no other object. This is not properly explained by relativity theory, only some vague appeal to "it must be to do with the distant stars". IF so, how?

 1035870.  Sun Nov 17, 2013 7:58 am I'm not sure why you're highlighting the word all, but anyway. Perhaps I missed one of the animals in the Lion King? Ok - you're saying people believed in a universal frame of reference - which no-one has proved to exist (or is unnecessary). And this could lead to people believing in absolute speeds (or motionlessness). But Einstein only showed you get interesting effects when you consider different frames of reference. And Newton was persuing a universal frame of reference - but still motion would be relative. People had already understood these relative frames of reference existed before any of these boffins even got out of bed.

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