My article “Cosmology Q & A” has been published! It appeared in the magazine Australian Physics, 51 (2014) 42-6 and is reproduced here with permission. After a brief overview of modern cosmology, it (tries to) answer the following questions:
- Is space expanding, or are galaxies just moving away from us?
- Is everything getting bigger?
- Ordinary matter and radiation cause the expansion of the universe to decelerate. But our universe is accelerating! How? What is the universe made of?
- Dark Energy? Is that like Dark Matter?
- How big is the universe?
- How big is the universe really?
- If the universe were finite, could I see the back of my own head?
- Is space expanding faster than the speed of light?
- Are there galaxies moving away from us at more than the speed of light?
- Light from distant galaxies is observed to be redshifted. Is this because the expansion of space stretches the wavelength, or because is it a Doppler shift due to the recession of the galaxy?
- Does the universe have zero total energy?
- Energy is not conserved!? Shouldn’t that send shivers up the spine of any physicist?
- The very universe, we are told, began in thermal equilibrium. How did equilibrium establish itself so quickly?
- How does the initially smooth universe we see in the CMB become today’s universe of stars and galaxies?
As before, further questions in the comments are always welcome.
Letters to Nature 
Hi Luke,
The article says: “If you find yourself in a spatially-curved universe and have handy a really big triangle and a lot of spare time, you will measure that its internal angles don’t sum to 180 degrees. It matters not what the triangle is made of; the curvature is written into space itself.”
But wouldn’t anything you used to measure the triangle with also be affected by the curvature too – and indeed everything else: matter, light etc etc? Is it really possible to detect the curvature of one’s local space in this way?
Everything is affected – which is why we can measure curvature. The effects don’t cancel out.
Remember – the curvature is a large scale property, like the curvature of the earth. But, we measure the angles of a triangle locally. The triangle could be a million light years in size, but to measure an angle you only need a protractor in each of the corners.
Thanks Luke. So the protractor would be curved too, but to a far lesser degree and would therefore detect that the very large triangle had corners ‘out of true’?
Cool.
Hi Luke,
Are you going write something about the gravitational waves discovery and its relation with the multiverse? Some people claim its evidence for the multiverse, what do you think ? And what about sean carroll-WLC debate ?
I’ve got something coming out soon about BICEP2 and the multiverse for another website. I’ll post it here.
I’m sure I’ll comment on Carroll-Craig eventually. I have a few comments. It was really rather good, on the whole. I haven’t yet listened to the 4 respondent talks on the day after.
I’d be lying if I didnt read the title of the article and think of Steve Irwin talking about how dangerous sub-atomic particles are–then wrestling one.
Luke,
You mentioned in your article that on cosmic scales energy is not conserved. I may not have grasped what you were saying, but if I understood you correctly wouldn’t this mean that one of the objections to the possibility of miracles is unwarranted, i.e. the notion that a miracle would violate the conservation of mass/energy in the universe? Am I right or am I not understanding something here?
Yep this is true. Robin Collins did an excellent paper on it. (In context he’s address objections to the soul based on energy conservation)
[…] We seem to need another ingredient in this explanation. That a brain can do theoretical physics and cosmology suggests not only that it is a remarkably adaptable, programmable thing, but also that the universe is an easier problem than we might have expected. A great example of this is the so-called cosmological principle. (I discuss this in more detail in my Australian Physics article here.) […]