Expansionof the universe and atoms... ?

[OneEyedSam]

I was comtemplating that the redshift of galaxies implies the expansion of space. 

We say that a galaxy is receding at a number of m/s ... but what is the meaning of meter in this case, i guess it means "earth meters"?  Is a a meter in a galaxy far far away a different length to an earth meter, although to the observer in the location they appear the same.  This is similar to the time , ie time appears to move slower rate as you approach light speed, but the observer wont notice the difference.

As space is expanding, what does that mean for the atom, is the atom expanding, and if it is,then doesnt that have some quantum effect that might affect the H-alpha line. I guess current theories say not, but why not ?    I guess if space is expanding at the same rate everythere, then I guess it doesnt matter, everything is being stretched at the same rate, we're all be playing by the same rules, but how come we notice red shift from receding galaxies.

So for us to notice red shift, space is expanding, yet atoms are unaffected. h-alpha is 656nm in all parts of the universe.

Arrgh. help !

[D4N]

On smaller scales Gravity overcomes expansion, this prevents matter from flying apart.

Sent from my iPad using Tapatalk

[OneEyedSam]

I figured it must be gravity, i guess i need to read up on this a little then

[Calculon]

I was comtemplating that the redshift of galaxies implies the expansion of space. 

Is a a meter in a galaxy far far away a different length to an earth meter, although to the observer in the location they appear the same.

Short answer: not necessarily.

Long answer: have a look at http://en.wikipedia.org/wiki/Proper_length and associated terms. To get into a question like that you have to very specific about what exactly you mean, and it's really not simple unfortunately!

[OneEyedSam]

thanks, I'll take a look

Once you scratch the surface you seen end up in the deep end, and the deep end is very deep !

[D4N]

Possibly even infinitely deep

Sent from my iPad using Tapatalk

[ronin]

If the expansion is as believed at present and there if it continues to accelerate it will eventually rip atoms apart.

However do not be too surprised if something new appears at some time.

Somehow it seems to have been decided that after about 100 years of a few theories that we "know" everything.

Truth is I suspect that we know close to nothing, and that some of the nothing is wrong.

The accelerted expansion is based on one aspect - red shift at very long distances is more then expected.

So the question is "Why this extra red shift?"

If there is a reason for that which we have not realised and therefore taken into account then there could be no acceleration, no dark energy and 75% of the universe is removed.

Less then 100 years back we didn't even know we had expansion.

At present we seem to be guessing about a huge amount of things and yet those guesses are suddenly "facts".

[OneEyedSam]

At present we seem to be guessing about a huge amount of things and yet those guesses are suddenly "facts".

We're layering theories on top of theories. Theories that fit evidence, thats what science does .. but did we take the wrong fork in the road at some point in the past to arrive where we are today, almost certainly in my view

Hopefully in my lifetime some bright spark will wake up one morning with a game changing idea.  It will be elegent and one of those "why didnt we think of that before" moments

[Crebles]

My understanding is that at the tiny tiny atomic scales, the strong and weak nuclear forces are far stronger than gravity and hold atoms together, whereas gravity acts (albeit relatively gently) over the immense distances of space. I understand dark matter and dark energy are needed to explain the (accelerating) expansion of the universe we observe. I think 'inflation' (as in the ultra rapid ballooning of space in the first moments after the Big Bang) is a slightly different concept to 'expansion'. Although the universe is getting bigger, I don't think atoms dilute or get less dense.

[cresskh]

A very important thing to note here is that only space is expanding and nothing else. Atom doesn't expand. Gravity, electromagnetic and strong and weak nuclear forces dominates the dark energy at small scales.

To imagine the accelerating expansion, it is always useful to imagine our universe is sitting on a surface of a balloon. As the balloon expands, every point on the surface is experiencing the same rate, and you will be that the further the object is away from you, the faster it is receding away.

And finally to answer your question of meter, the astronomers measure the amount of red shift observed and plug it into the Doppler shift equation. From there they will get the speed of the object moving away from us. And the unit of speed is always as we know it - meter(earth meter)/second

Sent from my Xperia ZR using Tapatalk

[Roy Challen]

If the expansion is as believed at present and there if it continues to accelerate it will eventually rip atoms apart.

However do not be too surprised if something new appears at some time.

Somehow it seems to have been decided that after about 100 years of a few theories that we "know" everything.

Truth is I suspect that we know close to nothing, and that some of the nothing is wrong.

The accelerted expansion is based on one aspect - red shift at very long distances is more then expected.

So the question is "Why this extra red shift?"

If there is a reason for that which we have not realised and therefore taken into account then there could be no acceleration, no dark energy and 75% of the universe is removed.

Less then 100 years back we didn't even know we had expansion.

At present we seem to be guessing about a huge amount of things and yet those guesses are suddenly "facts".

Well, not really. A true scientist wouldn't interpret their findings as fact until there was no way of proving otherwise. It's the media- even scientific media- that jumps on these so called facts, publishes them and then all of a sudden a whole bunch of pseudo science erupts to imprint these 'facts' on the minds of those don't know otherwise, who then tell everyone else etc.

[Cath]

what if someone where to mention that there are no facts, only interpretations ?

[Gazabone]

Or alternatively, atoms are constantly shrinking and therefore everything made of atoms is shrinking so the illusion is that we stay a constant size and everything moves away from us but in reality the space between galaxies simply appears to get bigger because we get smaller without knowing it.

Just an alternative way of looking at it and I await my theory to get shot down in flames.....

[cresskh]

If everything gets smaller, then we should see red shift everywhere but we see blue shift in locality, dominated by gravity.

Sent from my Xperia ZR using Tapatalk

[ronin]

what if someone where to mention that there are no facts, only interpretations ?

Agree entirely.

Expansion and accelerated expansion is because the red shift of galaxies at the limit are not in line with a set of predictions based on distance and velocity.

This being the Hubble const, however I would actually have thought that galaxies further away would have exhibitted greater red-shift and I certainly would not expect it to be linear. The present red shift seems a little too simple an interpretation.

We/they are seeing a greater red shift, it is the interpretation of that which is I think open to question.

As in what are the possible reason for this?

I can think of a simple one.

[gkec]

This appeared very recently which is pertinent

http://astronomynow.com/2015/04/13/universe-expanding-more-slowly-than-previously-thought/

[just_ed]

I'm not totally convinced that the red shift equals expansion. Considering the distances and times involved, I'm not sure that the speed of light is a constant. This is only an uneducated guess by me.

[Cath]

Pretty sure the speed of light is fairly constant in our part of the universe at least, although it has been reported that it can be altered in free space (as yet unconfirmed).

As to what state the universe is in many times out from that what we can see (40 odd billion years I think if you take into account the now actual position of the visible galaxies) is something we can only sumize at.

[OneEyedSam]

How safe is the assumption that the strength of the various forces and other constants, really are constant. 

Take the speed of light for example, we know the speed isnt constant already otherwise the lenses in our telescopes and eyepieces wouldnt work.  Its summised to be a constant in a vacuum.  But constant over an expanding space ? and is space a vacuum, how is its speed altered by for example, dark matter, solar winds, heavy objects such as galaxies and superclusters.

[cresskh]

It's a common misconception of the Special Theory of Relativity. It postulates that speed of light is constant in vacuum. So when light changes its speed in different medium, it doesn't violate the theory at slightest bit. Even when a vacuum space is expanding, the light still travels at same speed but through a ever longer distance and wavelength is stretched to the red end of the spectrum.

However, there is no assurance that all the nature's constants remain constant at all places all times. There might be a place in remote part of our universe where speed of light is slower, gravity is stronger, electric charge is weaker, etc, we wouldn't know.

Read The Constants of Nature by John D. Barrow. It's a good book

Sent via Tapatalk

[OneEyedSam]

ok, thanks for the tip off on the book    £2.81 on amazon inc shipping

[Physicist13]

clearly we need to do more outreach........ This topic comes up so much. More physicists on TV maybe?!!..... 

[George Jones]

A technical paper that addresses this question (at the level of a final-year physics undergrad) is "In an expanding universe, what doesn’t expand?" by Price and Romano,

http://arxiv.org/pdf/gr-qc/0508052v2.pdf

A somewhat less technical synopsis of the paper can be gained by read the abstract, the first three paragraphs of the Introduction, and the first paragraph of the Conclusion.

Those with a technical background might want to read more of the paper.

[OneEyedSam]

thanks, I'll dust off my maths and give it a read