Perhaps you've heard this annalogy before, it's called "spots on a balloon". First you take a balloon with no air in it, and draw a cluster of dots close together. Now, inflate the balloon. Each point moves away from all the others. This is how the Redshift is interpretted. It is assumed that if you stood in some other part of the universe, you would still see everything, including Earth, moving away from you.

BTW, this doesn't work on the small scale. Other stars in our system, other systems in our galaxy, and other galaxies in our local cluster can be seen to have a Blueshift (presumably because they are being pulled together by gravity). Only on the really grand scale, the distances between galactic clusters, do we see a more-or-less uniform Redshift.

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Originally posted by LURCH_001:
"Wherever you are is the center of your own universe".

Perhaps you've heard this annalogy before, it's called "spots on a balloon". First you take a balloon with no air in it, and draw a cluster of dots close together. Now, inflate the balloon. Each point moves away from all the others. This is how the Redshift is interpretted. It is assumed that if you stood in some other part of the universe, you would still see everything, including Earth, moving away from you.

BTW, this doesn't work on the small scale. Other stars in our system, other systems in our galaxy, and other galaxies in our local cluster can be seen to have a Blueshift (presumably because they are being pulled together by gravity). Only on the really grand scale, the distances between galactic clusters, do we see a more-or-less uniform Redshift.

Why do they call it a FIXED income, when I'm always BROKE ?!

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That works for the dots on the surface of the balloon but what about inside the balloon?

Hurkyl

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Originally posted by Hurkyl:
In this analogy, the inside of the baloon simply doesn't exist; the universe is only the surface of the balloon.

Hurkyl

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Then we can only travel in one direction- outwards with the balloon?

In the balloon analogy, space is two-dimensional: we can only crawl along it like ants. To our 2D selves, there is no "outward" movement, just distances getting bigger as time goes by.

From the balloon, you might think that a space with no center and no edge has to curve back on itself: this isn't true, it's just an artifact of us only being to think in a measly 3 dimensions.

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Originally posted by alis:
Even on a global scale galaxies/clusters are not uniformly redshifted wrt us. It's really hard to measure this, because of the inadequecies of independent distance measurements (eg standard candles) in distant galaxies. But IIRC most recent work finds the grand-scale center-of-momentum frame is moving ~400 km/s w.r.t. roughly in the direction of Virgo. This is in agreement with the observed CMBR dipole anisotropy.

In the balloon analogy, space is two-dimensional: we can only crawl along it like ants. To our 2D selves, there is no "outward" movement, just distances getting bigger as time goes by.

From the balloon, you might think that a space with no center and no edge has to curve back on itself: this isn't true, it's just an artifact of us only being to think in a measly 3 dimensions.

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The good Christian should beware of mathematicians and all those who make empty prophecies. The danger already exists that mathematicians have made a covenant with the devil to darken the spirit and confine man in the bonds of Hell. -St Augustine

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Ok, so the balloon analogy is not correct then since we don't live in 2 dimensions and there is blue-shift on a grand scale. Do you have a link for this observation?

Also, is matter being expanded along with space? If so, shouldn't matter get larger also? Or do the BB believe only the outer edge part of space is expanding?

See "The influence of the cosmological expansion on local systems" - http://xxx.lanl.gov/abs/astro-ph/9803097

So, if we are detecting only redshifts on the grand scale, doesn't that mean that we are at the center of the universe with all galaxies accelerating away from us? Doesn't that also mean that those galaxies are probably accelerating faster than the expansion rate of space since otherwise we, at the center of the universe, wouldn't be able to detect redshifts on the cosmological scale if the rate of expasion is uniform?

If so, wouldn't the galaxies soon have, literally, no place to go?

Another puzzling thing is how can they expand? Going back to the balloon analogy, we can see the small dots getting bigger (and less dense) and the distance between them growing but what is blowing up the balloon?

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Originally posted by meteor:
You don't have to mix cosmological redshift with doppler redshift. Even if the galaxies are expanding at the same rate(they are like fixed in a point of the space), the light that they emit is redshifted.This is the cosmological redshift. Apart of this, the peculiar movement of the galaxy despite of the expansion of the space causes the doppler redshift, that can be compared to the change of pitch of the sound of a train that comes to you or go away

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Ok maybe you can explain for me how, if everything in the universe- space, matter, energy - is expanding at the same rate, does the photon end up having a longer wavelength than before?

The photon wavelength may have grown longer but the dimensions of the instrument used to measure its wavelength at the final time is also larger in all dimensions by the same proportion- so how would it measure a difference?

It seems more likely that the measured redshift is the doppler redshift where the source is actually moving relative to the observer. And if we are only observing Doppler (and not Cosmological) redshifts on the large scale, we should have to conclude we are at the center of the universe, under this expansion model. Also, the galaxies should have fell out of space a long time ago.

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Originally posted by meteor:
The wavelenght of the photon increases, but the measuring instrument does not becomes bigger. The fact that space is expanding doesn't mean that the objects increase in size. The nuclear forces prevent it

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How does the nuclear force prevent the object from growing in size? All the matter and energy in the universe on a dime wasn't enough to prevent space from expanding to its size now, why should the expansion of space now be affected by a mere nuclear force between the few molecules on a planet? There is supposed to be some space between electrons and atoms- I don't see how the EM forces here can possibly prevent space from expanding. How about the bonds in liquids? Are they strong enough to keep the atoms together as space is stretching itself out? It would seem that if such weak forces are enough to prevent space from expanding, space would have most difficult time expanding.

And why would the photon expand if other types of matter didn't?

Even if we assumed, falsely, only the photon wavelength increased, the speed
of the photon would still have to be c as the space is expanding. So, as time passes and the distance between the source and observer is expanded, the observer would also observe a longer time for the travel of the photon (even though the source and observer were both stationary).

So, does light speed up as time goes by or do we now make up a time dilation for this situation as well?

A more consistent model of expansion, imo, is one that assumed space and matter to be expanding in all dimensions at the same time (but the energy and matter doesn't change, it just gets less dense). In this case though,
the redshift observed would be a Doppler redshift resulting from the acceleration of the galaxies being faster than the expansion rate of space.

The best version of the BB actually is one that assumes space to be infinite and it is only matter+energy that are moving away from each other from an initial explosion- space remains constant and infinite. But here, the redshift we observe in all directions could only mean we are at the center of the universe.

In short, the BB is problematic.