I’ve been a bit quiet around here, lately. Travel is my excuse. I’m currently in Cambridge, collaborating with a few colleagues on a project. I’ll be back in Sydney next week, so if you’re near Epping on Friday 4th July 2014, why not come along to hear me speak at the Astronomical Society of NSW:
“What Happened at the Big Bang?”
Friday 4th July 2014 – 8:00pm
Topic: What happened at the Big Bang?
Speaker: Dr Luke Barnes, University of Sydney
Venue: Epping Creative Centre – 26 Stanley Road, Epping
Abstract:
Was the big bang the beginning of the universe? Does the big bang represent the beginning of time itself? This is an age-old question, and has been remarkably informed by modern cosmology.
I will answer this question once and for all.
I will follow the theorems, evidence and hints that lead us back in time. In particular, I will discuss the expansion of the space, the physics of the very early universe, the recent BICEP2 results and cosmic inflation, the effect of quantum physics, and the reason (or one of them) why Stephen Hawking is famous.
Biography:
Dr Luke A. Barnes is a postdoctoral researcher at the Sydney Institute for Astronomy. After undergraduate studies at the University of Sydney, Dr. Barnes earned a scholarship to complete a PhD at the University of Cambridge. He worked as a researcher at the Swiss Federal Institute of Technology (ETH), before returning to Sydney in 2011. He has published papers on galaxy formation and cosmology, and recently has taken an interest in the fine-tuning of the universe for intelligent life. He blogs at letterstonature.wordpress.com.
Letters to Nature 
Hi dr. Barnes,
Was this recorded? Hope this can be made available soon 🙂
Hasn’t happened yet. I’m trying to get a video camera to record it.
How did it go? Were you still able to record it? I think we all look forward to your thoughts regarding the Big Bang.
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Hi Luke,
I enjoyed your recent Bayesian lecture. I do wonder about the irony of your example involving the patient with a positive test result–Given the probability of false positives, what is the probability that this particular patient actually has the disease in question?
The irony of this example is that in order to use the Bayesian method effectively, we must have some means of finding the probability of false positives. How do we do this in practice? Well, we just count them; that is, we become “frequentists.” So on the right side of Bayes theorem we have a frequentist estimate yielding a Bayesian result for probability on the left side.
My suspicion is that this operation, although very useful, tends to give many users too much false confidence in Bayesian probabilities. I would favor calling the left side of Bayes theorem the “estimated probability,” to avoid the trap of sweeping our ignorance under some rug. In this case the actual probability would be an abstract idea as in the classical theory of stochastic systems.
Am I missing something?
Paul
Paul L Nunez PhD
Cognitive Dissonance LLC
Emeritus Professor Tulane University
Paul L Nunez PhD
Cognitive Dissonance LLC
Emeritus Professor Tulane University
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For the Bayesian, probabilities are informed by data, and so probabilities are informed by frequencies. What the Bayesian denies is that probabilities *are* frequencies. Under certain circumstances – and the Bayesian can give an account of when those circumstances are – probabilities will be numerically equal to frequencies.
This is not the same as a “frequentist estimate”. There are probabilities that the Bayesian can calculate that the frequentist cannot even define, such as the probability of general relativity given our observations of the solar system. We can’t observe more than one universe, so we can’t count the number that obey general relativity.