I’ve invited cosmology questions before, but I wanted to renew the call. I’ve got a Q&A article on cosmology coming out soon, so ask away!
More Cosmology Questions
February 11, 2014 by lukebarnes
Posted in Uncategorized | Tagged cosmology, Physics, Science, universe | 26 Comments
26 Responses
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I know this is a quite far-fetched. I know it strains credulity. But (ignoring the theological and philosophical questions such as a deceptive God) is there any conceivable chance it’s at least hypothetically possible the Ken Ham ‘Young Earth Creationists’ of the world ‘might’ be correct that the age of the universe is thousands rather than billions of years old? That the speed of light isn’t constant? Or is what they say utterly implausible by any modern scientific account?
Highly unlikely, due to the finite speed of light. No evidence of speed up. Creationist models require the speed of light to have levelled off in 1960. I haven’t looked at the other models in any great detail. I doubt it.
I have two areas I’d be interested to see discussed please, to help the understanding of non-scientific people.
1. You have criticised Lawrence Krauss and his “universe from nothing”, but what would the current consensus be among cosmologists generally – is it with you, or him, or divided, or do most think it isn’t a scientific question?
2. I have two questions about fine-tuning:
(i) If the multiverse is a scientific possible explanation of fine-tuning which has some theoretical support (as both Rees and Susskind say), then has there been any scientific discussion of how fine-tuned the multiverse would need to be to produce 10^500 universes each with different properties, or is that way too speculative for anyone?
(ii) I have loved watching and reading your explanations of all the different facets of fine-tuning, but they are pretty complex for a lay person like me. It would be wonderful if you produced a short summary of the evidence with minimal maths – sort of “fine-tuning for dummies”. 🙂
Thanks.
1. I don’t know, actually. I’m not sure how many cosmologists read popular science.
2. (i) Very speculative. The most convincing argument is that, through inflation, a universe that starts just about anywhere in the landscape will diffuse through the rest of the landscape.
(ii) Stay tuned …
When light travels through expanding space its wavelength increases, thereby lowering its energy. Where is that energy lost to?
Energy is not conserved in cosmology. More details soon!
Oh, and: light emitted from objects travelling towards us are blue-shifted because the crests of their waves are compressed closer together (right? there’s a more elegant way of putting that, I know, but I’m sure you get what I mean.) That makes sense for streams of photons… since the crests of multiple photons can be bunched up like that… but what about a single photon emitted from an object moving towards us… can a single photon be blue-shifted?
The rate at which photons arrive does not give their wavelength. So it doesn’t make sense for streams either.
A single photon is described as the quantisation of a field, and the field “stretches”. In the end, relativity describes the energy of a particle, and how it depends on one’s path through spacetime. So relativity tells us that the energy of the photon changes with the expansion, and quantum mechanics tells us that the energy is proportional to the frequency.
What do you think of Jason Lisle’s Anisotropic Synchrony Convention?
I don’t know. I might have a look sometime.
I really liked this blog. It’s hopeful and true. Keep writing, you have a fan. 🙂
What is inflation? Does it explain the fine-tuning, or complicate the fine-tuning problem?
I cannot agree more with unkleE. I believe you’re the best person to write a “Fine-tuning for Dummies” book….
We never really witness anything springing into existence out of nothing. How can you then say that quantum mechanics explains the birth of the universe? How can something just suddenly come into being out of nothing? We have no real-world analogies do we?
Something from nothing? Nope. More here: https://letterstonature.wordpress.com/2011/04/16/more-sweet-nothings/
Inflation: that’s a big question. Stay tuned for the article.
Another question. From what I have read, Roger Penrose estimated the odds of obtaining our world by chance were 1 in 10^10^123, while the number of domains in the multiverse is sometimes said to be 10^500.
Are these figures generally accepted? If so, how is the multiverse a possible explanation for fine-tuning, since 10^500 is still only a tiny fraction of 10^10^123?
Thanks.
10^500 is the number of possible low-energy “effective laws of nature” in string theory. Its the number of possibilities, not the number of universes. 10^10^123 is generally accepted, but entropy and cosmology is a famously tricky subject.
Universe with wells. Why explain gravity as wells you can fall into. Drawings with those wells look fancy, but for me that’s it. Occam’s razor makes me think these well is an unnecessary addition to the theory of gravity and the universe.
The wells are a metaphor, an image used to try to explain the considerable complications of general relativity to the mathematically uninclined. the point of the analogy is that objects moving under gravity travel along locally straight lines (geodesics); energy distorts the very structure of spacetime beneath them. Gravity doesn’t turn the steering wheel; it banks the curve.
Something must be eternal. But what.
What do you think of A and B Theory of Time? Which do you believe to be correct?
No idea. I don’t know how you put the A theory and relativity together. I don;t know who you reconcile the B theory with our subjective experience of the passage of time.
Hi Luke
One thing I would really appreciate being cleared up, and I think many of us would too, is this BGV theorem. It’s unclear to me exactly what it implies, could you maybe write a post for us clearing it up? You have Craig and others saying it implies a beginning on just about any cosmological model, and then atheists (who are also cosmologists) like Krauss and Carroll denying that implication or dodging it somehow. What is the truth? What exactly allows one to dodge the implications and what range of these cosmologies does the theorum cover?
Thanks!
A hot Big Bang, or a cold slow thaw?
http://www.sciencedaily.com/releases/2014/02/140225111921.htm
. Wetterich’s model explains dark energy and the early “inflationary universe” with a single scalar field that changes with time, with all masses increasing with the value of this field. “It’s reminiscent of the Higgs boson recently discovered in Geneva. This elementary particle confirmed the physicists’ assumption that particle masses do indeed depend on field values and are therefore variable,”
I would be interested in knowing a bit more in detail, how one could determine experimentally if we were to live in a multiverse. I understand that there are several different different types of multiverses, and I am not interested in those which are purely philosophical (e.g. David Lewis) or experimentally non-feasible. I am thinking of theoretical models which could be verified experimentally- e.g. Andrei Lindes “Inflationary multiverse and eternal chaotic inflation”, Lee Smolins idea of new universes being spawned from black holes etc.
Thank you
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