The Naked Scientists

The Naked Scientists Forum

Author Topic: Forget gravity, how does andromeda know the milky way is attracted to it.  (Read 2728 times)

Offline acecharly

  • Sr. Member
  • ****
  • Posts: 171
    • View Profile
How do these two galaxies or any other two know each other are their and pull to one another? Physics talks of the graviton, well it must be big to stretch from one galaxy to another. Some may say theres lots of them stretching from one galaxy to the next, but then there must be some kind of communication between them all which must be instant and unaffected by time id have thought.

Any thoughts

Cheers Ace


 

Offline imatfaal

  • Neilep Level Member
  • ******
  • Posts: 2787
  • rouge moderator
    • View Profile
They know they are there because space-time is curved due to the mass/energy of the galaxy.  the disturbances/curvature spreads out at the speed of light (not instantly) and the galaxies (or in fact the individual stars/planets/dust etc) follow the straightest path through the curved space.  As at any moment of time the spacetime will be curved then the galaxies are not acting under an instantaneous force.  The old chesnut model of the rubber sheet with a mass pulling it down is a good aid to understanding in this case

Gravitons are more difficult to conceive - they are virtual particles as are the other gauge bosons; and thus a real world naive (in a nice way) view of them is practically impossible.  We can correctly predict a lot of stuff by viewing the Electromagnetic force as the exchange of virtual photons, the Strong as exchange of gluons and the Weak by W &Z bosons - these Quantum Field Theories are immensely strong, give highly accurate predictions, have lead to other discoveries etc.  But whether they are a "correct" view of the world is pretty unimportant.  Science isn't really about the most basic under-pinning truth and reason - it's about explaining observations with repeatable and quantifiable models.

The maths and models behind the graviton are not yet complete - and we are searching for it and developing the theory because the other QFTs of the standard model are so damned good
 

Offline acecharly

  • Sr. Member
  • ****
  • Posts: 171
    • View Profile
.  Science isn't really about the most basic under-pinning truth and reason - it's about explaining observations with repeatable and quantifiable models.


I think a few people would disagree with the first part of your statement. The second part is surely the precursor to physics's endgame theory of everything or there would surely be no point.
 

Offline Geezer

  • Neilep Level Member
  • ******
  • Posts: 8328
  • "Vive la résistance!"
    • View Profile
.  Science isn't really about the most basic under-pinning truth and reason - it's about explaining observations with repeatable and quantifiable models.


I think a few people would disagree with the first part of your statement.

They probably would, but Imatfaal is correct. Insight into truth and reason is a consequence of the patient development of scientific models.

For example, Galileo did not set out to turn cosmology on its head. He was just using a new invention to take a look at the objects in the sky.
 

Offline Soul Surfer

  • Neilep Level Member
  • ******
  • Posts: 3345
  • keep banging the rocks together
    • View Profile
    • ian kimber's web workspace
We can see the Andromeda galaxy quite easily this shows that light from it has had plenty of time to reach us so the gravitational field has also had plenty of time to reach us.  Anything that is visible to us must be included into the equation that defines what gravitational fields are acting on us.  but going right back to the cosmic microwave background this eventually smoothes out because it is almost exactly the same in all directions
 

Offline imatfaal

  • Neilep Level Member
  • ******
  • Posts: 2787
  • rouge moderator
    • View Profile
.  Science isn't really about the most basic under-pinning truth and reason - it's about explaining observations with repeatable and quantifiable models.


I think a few people would disagree with the first part of your statement. The second part is surely the precursor to physics's endgame theory of everything or there would surely be no point.

per Geezer.  Would also add - there is always another level of "Yeah but why does it do that?"  We seek to model and understand that which we can observe - not to ferret out the most fundamental reason; because that most fundamental reason will still be vulnerable to "OK - but Why?"
 

Offline acecharly

  • Sr. Member
  • ****
  • Posts: 171
    • View Profile
.  Science isn't really about the most basic under-pinning truth and reason - it's about explaining observations with repeatable and quantifiable models.


I think a few people would disagree with the first part of your statement. The second part is surely the precursor to physics's endgame theory of everything or there would surely be no point.

per Geezer.  Would also add - there is always another level of "Yeah but why does it do that?"  We seek to model and understand that which we can observe - not to ferret out the most fundamental reason; because that most fundamental reason will still be vulnerable to "OK - but Why?"

I see what your saying now imatfaal we can never be sure we understand everything i miss-understood you sorry.

I was watching a video of the tsunami that hit indonesia several years ago on christmas day and noticed how the water was receeding back into the ocean after it had hit. Could the gravitation effect be similar between our galaxies sucking both towards each other?
 

Offline imatfaal

  • Neilep Level Member
  • ******
  • Posts: 2787
  • rouge moderator
    • View Profile
I am not sure if that analogy is useful; and that's not just a nice way of dismissing it, I really am not sure.   I don't know of a good real world analogy that helps one to "get" General relativity. 
 

Offline imatfaal

  • Neilep Level Member
  • ******
  • Posts: 2787
  • rouge moderator
    • View Profile
Think of the old rubber sheet analogy.  You have a very wide and taught rubber sheet.  On it you place two dumbells (one is milky way and other is andromeda) - the dumbells' axes are aligned, and the sheet is distorted but not enough to make the dumbells tip or slide. 

if you roll each dumbbell forward it will follow it's own geodesic - the way a dumbbell rolls means that it will travel the equivalent of a straight line on a curved surface ie the geodesic.  If you roll the two dumbbells forward you would note that their paths get closer and closer together - and the rate at which they are drawn together increases.   the change in position is communicated to the other dumbbell by the change in the curve of the rubber sheet (if you tried it - the speed of the change would be the speed of a wave through the rubber sheet) - there is no need for instant communication, but there is no lag because updating is continuous.

This is the very rough equivalent of what is happening - but in 2 dimensions, one of space and one of time - we of course have three of space
 

Offline yor_on

  • Naked Science Forum GOD!
  • *******
  • Posts: 11999
  • Thanked: 4 times
  • (Ah, yes:) *a table is always good to hide under*
    • View Profile
I don't really know Ace. The description of 'how' doesn't really capture the 'why' :)
Most of what we think us to know gets challenged when you start to look at physics. SpaceTime in Einsteins way is a isotropic homogeneous entity, warped by 'gravity' as I understands it. Gravity is the metric defining the space we observe.

It's like everything consisted of incredibly thin ribbons, able to bend in all weird kind of ways. Some parts/positions of/on those ribbons are denser than others, representing matter. But then you have the arrow (time) moving those positions in the ribbons in yet a new dimension, creating (possibly that is:) the relative motion we find and describe. And then to that you can add that it is observer dependent, the whole shebang is observer dependent. And that means that your description of time and distance isn't mine.

( The last part relates to observations between frames of reference naturally, as you measuring some other frames clock and 'distance', as defined by your wristwatch and ruler.)
« Last Edit: 05/07/2012 16:33:16 by yor_on »
 

Offline loose_nukes

  • Jr. Member
  • **
  • Posts: 15
    • View Profile
I don't really know Ace. The description of 'how' doesn't really capture the 'why' :)

Exactly yor_on..........................To understand the ultimate WHY, one needs to consider the GOD question. Because this is a science forum, the GOD question, will most likely, never be answered.
 

Offline evan_au

  • Neilep Level Member
  • ******
  • Posts: 4126
  • Thanked: 247 times
    • View Profile
Another approach: As well as the general motion of stars and galaxies, each star or galaxy has its own, random, "proper motion".

At this point in time, Andromeda and the Milky Way have proper motions that are towards each other, and this would continue even if gravity were not acting between them.

We know that gravity is acting, so their closing velocity will increase before they meet.
 

The Naked Scientists Forum


 

SMF 2.0.10 | SMF © 2015, Simple Machines
SMFAds for Free Forums