Accelerating universe - details and dispute

[gth759k]

"accelerating" universe - details and dispute

I recently sent an email to several physics professors at CalTech and MIT with a question I have about Cosmology and only one professor (Walter Lewin) replied simply saying good luck! Its not so much of a question as it is a problem. I've talked to people about this before and the conversation quickly looses all basis in reality and data and becomes more like something out of a science fiction novel. So, if you should choose to reply please stick to the facts and leave out the suppositions. That means I don't want to hear anything like "stretchy" space-time unless you can back it up with systematic, uniform and precise data and theory, because I will not take you seriously. So, on to the problem.

According to many sources (on the web and off) ... the universe is accelerating! Very notable scientist currently argue that the universe is not only expanding, but expanding at an accelerating rate. So I set about searching for the evidence of this claim and I was pointed to many sites on redshift and spectography and physics equations. Eventually I found the image above which is most interesting to me. There are many others like it showing the same data trends. I don't know about you, but I can't think in megaparsecs, so the first thing I did was convert the units from megaparsecs to kilometers. The closest type 1a nebula on the graph in the lower left hand corner is about 35 Mpc = 1.0799 x (10^21) km and the farthest nebula in the upper right hand corner of the graph is about 635 Mpc = 1.9594 x (10^22) km. These values on the horizontal axis were approximated, as I understand using the magnitude-distance formula which uses the absolute and apparent magnitudes of the nebula to determine the distance. The vertical axis on the chart shows the (approximate) velocity in km/s of the nebula relative to us calculated using Hubble's law. Now, let me ask you a question, what does this chart show us? I've been told that this chart shows that the farther away a celestial body is the faster its going! Hmmm ... I disagree. I think this chart shows that the farther away a celestial object is, the faster it WAS going. I say that because, and I'm sure you'll agree, we see the galaxies and nebula as they WERE and not as they are. In other words, if an event was observed in M31 it would be more recent than a event observed that very hour in M82. So, do we all agree that the farther away you look, the deeper you're looking into the past? Then, when we look at the most distant objects we are seeing a picture of the early universe right? So doesn't that mean that the (farthest) fastest objects we find are a picture of the early universe too? And that the closer, more resent, (slower) objects are more recent? In that the data contained in the light from nearby galaxies shows a more recent past than the distant galaxies? Then the velocities of the closest galaxies and nebula are a better representation of what the universe is really like right now because they represent a relatively fresh past. It looks like to me, if you reconstruct the events according to the data, that the early universe was moving away from us faster than the more resent universe. Not the other way around.

I'd just like to put my thoughts out there because when people start talking about things like "stretchy" space-time, it feels like all reason and common sense just go out the window.

 

[Driftwood1]

all the data points on the graph are for different supernova at different distances.

What the data points have in common is that they were all measured or observed at the same time!

For the universe to be expanding at a constant rate the Hubble plot must produce a straight line.

The problem that I have with the above graph is that a deviation from linearity at the greater distances cannot be confidently assumed (the error bars of the outer data points still stay within the straight line)

Are there any more data points that confirm the accelerating Universe hypothesis?

 

[Chalnoth]

So, do we all agree that the farther away you look, the deeper you're looking into the past?

Yes. This is taken into account in proper treatments of the issue. The fact remains that the far-away supernovae are too dim to be explained by a non-accelerating universe. The accelerated expansion makes far-away supernovae more dim compared to nearby supernovae than a non-accelerated expansion does.

 

[Ich]

BTW, the data you present all shows the very recent past of the universe, out to z=.1. Accelerated expansion is seen at redhifts z~.5. http://www.astro.ucla.edu/~wright/sne_cosmology.html" 's the relevant data, together with curves. As Chalnoth said, the curves have been calculated with the time variation taken into account. Did you really expect thousands of highy skilled and educated astrophysicists to miss such a fundamental fact?
Also, the "velocity" they're referring to in your plot really are c*z, a model-independent measure of redshift. And the distances are "luminosity distances", not "real distances" or whatever you might call it.

 

[Driftwood1]

a straw man burns quickly