Could the acceleration of expansion (of the universe) be an optical illusion?

[pdxfetal]

Physics & astronomy are interests of mine (I don't understand the granular details & apologize if this is a silly question)

Could it be that the increasing rate of expansion be similar to how two points on a balloon would appear to distance themselves as you fill it with air?

 

[PAllen]

Physics & astronomy are interests of mine (I don't understand the granular details & apologize if this is a silly question)

Could it be that the increasing rate of expansion be similar to how two points on a balloon would appear to distance themselves as you fill it with air?

Welcome to physics forums.

If we stick with your balloon analogy, accelerated expansion means the rate of inflation of the balloon is increasing. Steady filling of the balloon would be the crude analogy of non-accelerating expansion.

While acceleration of expansion is certainly not established at the same confidence level as, say, quantum mechanics, it went from being met with skepticism, to the current situation where there are no really credible alternative explanations of the accumulated observations. I believe the last major alternative was that our galaxy being a vast low density void could explain the results. Further observations have ruled this out.

 

[pdxfetal]

Thank you for the response! So if the 3 dimensions of the universe that we know were only represented by the rubbery material of the balloon and the gas used to fill the balloon wasn't visible from our vantage point wouldn't the steady expansion appear to be accelerating as the rubber stretches?

 

[PAllen]

Thank you for the response! So if the 3 dimensions of the universe that we know were only represented by the rubbery material of the balloon and the gas used to fill the balloon wasn't visible from our vantage point wouldn't the steady expansion appear to be accelerating as the rubber stretches?

The balloon is a really crude analogy that you can't stretch too far. What is really going on is comparison of observations to actual model of expansion, and finding that observations don't fit the simple un-accelerated models.

However, to continue a moment with the balloon, uniform increase in volume of balloon leads to recession velocities between marks on the balloon that are proportional to distance (the further away the marks are, the faster they move apart as the balloon fills a bit more). This is speed proportional to distance is what was expected for uniform expansion. Accelerating expansion predicts deviations form this, of the form that we observe.

 

[twofish-quant]

I believe the last major alternative was that our galaxy being a vast low density void could explain the results. Further observations have ruled this out.

Has there been any news since late April? Since as of 4/29/2011 the Witshire model hasn't been ruled out.

https://www.physicsforums.com/showthread.php?t=493096

The latest paper that I know of is here

http://arxiv.org/abs/1102.2045

 

[twofish-quant]

Could it be that the increasing rate of expansion be similar to how two points on a balloon would appear to distance themselves as you fill it with air?

It turns out that if you work through the observations that the expansion is faster than what you see if you assume a balloon.

What people measure is the Hubble constant which is roughly the rate at which the balloon is expanding. If it is expanding like a balloon, then H is going to be constant. What we are seeing as we take nearby measurements of supernova is that H seems to be increasing as you see nearby galaxies.

Also, I encourage people to read the original Riess paper, since it's an excellent example of scientific argumentation

http://adsabs.harvard.edu/abs/1998AJ...116.1009R

If you look at the headings, you will see a lot of "did you consider the possibility that what you are seeing is ?" with a paragraph "yes we did consider the possibility that what we are seeing is ? but we don't think so because of ****"

 

[PAllen]

Has there been any news since late April? Since as of 4/29/2011 the Witshire model hasn't been ruled out.

https://www.physicsforums.com/showthread.php?t=493096

The latest paper that I know of is here

http://arxiv.org/abs/1102.2045

Interesting. I was thinking of the simpler void models, which have been pretty much abandoned. I had not heard of Wiltshire's model, or his continued defense of against the latest data. So, I'm glad I used defensive formulation: not an established fact, but a working consensus.

 

[PAllen]

Here is a paper citing your Wiltshire link that gives general, but not firm, counter-argument. It agrees with Wiltshire on the key point that we need better data on the scale at which homogeneity sets it. However, if I have interpreted it right, it suggests that inhomogeneity at the currently accepted scale cannot account for the apparent acceleration.

http://arxiv.org/abs/1105.3450

And here is a review article recommended by the above, that also cites Wiltshire:

http://arxiv.org/abs/1103.2335

So this still looks like an active research front. I personally would love to be rid of dark energy. Dark matter, on the other hand, seems close to an established fact to me.