# Expansion of spacetime and matter [duplicate]

When space expands, light is said to be stretched or red-shifted. In fact, Penzias and Wilson discovered this in 1965 and were awarded the Nobel prize in Physics for this discovery.

Now, what I am confused with is whether the expansion of space into itself affects matter or in other words, how does expansion of space affect matter?

Does space expansion also mean time expansion?

## marked as duplicate by John Rennie general-relativity StackExchange.ready(function() { if (StackExchange.options.isMobile) return; $('.dupe-hammer-message-hover:not(.hover-bound)').each(function() { var$hover = $(this).addClass('hover-bound'),$msg = $hover.siblings('.dupe-hammer-message');$hover.hover( function() { $hover.showInfoMessage('', { messageElement:$msg.clone().show(), transient: false, position: { my: 'bottom left', at: 'top center', offsetTop: -7 }, dismissable: false, relativeToBody: true }); }, function() { StackExchange.helpers.removeMessages(); } ); }); }); Feb 10 '17 at 6:04

I don't think the expansion of the universe matters the matters, it's just the distance between objects have changed.

The change of the space-time fabric caused the distance between the light source and the observer to change, making it seems like its moving away from you, therefore this red-shift thing happens.

I don't actually have suggested readings but I can recommend you to read the book Black Holes and Time Warps-Kip Thorne, it talks about interesting theories and histories about space-time warpage and black holes. The Universe In Your Hand-Christophe Galfard is also a great book I enjoy reading.

The raisin bread model of the expansion or the universe helps in getting an intuition of what is happening:

The specific form of Hubble's expansion law is important: the speed of recession is proportional to distance. Hubble expressed this idea in an equation - distance/time per megaparsec. A megaparsec is a really big distance (3.26 million light-years). The expanding raisin bread model at left illustrates why this proportion law is important. If every portion of the bread expands by the same amount in a given interval of time, then the raisins would recede from each other with exactly a Hubble type expansion law. In a given time interval, a nearby raisin would move relatively little, but a distant raisin would move relatively farther - and the same behavior would be seen from any raisin in the loaf. In other words, the Hubble law is just what one would expect for a homogeneous expanding universe, as predicted by the Big Bang theory. Moreover no raisin, or galaxy, occupies a special place in this universe - unless you get too close to the edge of the loaf where the analogy breaks down.

The expansion of the dough in the oven , in which the raisins are embedded does not affect the size of the raisins. That is because the dough is very elastic and expands, while the raisins are held be much stronger cohesive forces.

For the same reason , the effective "force" of expansion due to the Big Bang is very much smaller than the gravitational attraction that holds galaxies together so does not affect their size. It is more so for atoms and matter as we know it which is held together by forces orders of magnitude larger than the gravitational force.

• I couldn't agree the fact that matter isn't stretched because of the forces in between the atoms outweigh the gravitational expansion. If you would provide more reference to the issue, it will be more enriching – Jyotishraj Thoudam Feb 14 '17 at 4:11
• @jyotishrajthoudam You must realize that a universe expanding steadily like from an explosion carries along the bound by forces matter because there is no dp/dt , i.e. a force . In the simple Big Bang the force was once in the beginning. In the present Big Bang model there is still an acceleration which introduces dark energy, which gives an accelerated expansion, that may change the stability of matter in the future en.wikipedia.org/wiki/Big_Rip – anna v Feb 14 '17 at 5:23
• @jyotishrajthoudam see also this arxiv.org/abs/0810.2712 as well as links in comments of the duplicate – anna v Feb 14 '17 at 7:28