Well I've finally finished the text in the latest iteration of the galaxy formation paper so I have a bit of free time to write.
When creating my last post on just thinking about stuff I had a lot of fun and also stimulated quite a bit of interesting debate so I thought I'd do it again with a few more fun things to ponder:
Oh God! Oh God! We're All Going to Die
Not only are you going to die but everybody you know is going to die and in the end, every single human being that ever existed will be die. And then humanity will cease to exist.
Cheery, huh.
Well wouldn't it be nice to know how long we have before the whole of humanity dies out? One very compelling argument comes from Brandon Carter (incidentally the same guy who also introduced the anthropic principle) and goes as follows...
Consider the total number of human beings that ever have, or ever will, live (N), and our position in a chronological list of all humans that will exist (n). The fraction of human beings that were born before us is f=n/N
The Copernican principle suggests that since we are not special observers that n should be uniformly distributed between 0 and N. Let us further assume that our fractional position f is uniformly distributed between 0 and 1 even after we learn of our absolute position n. This is equivalent to the assumption that we have no prior information about the total number of humans, N.
If f is uniformly distributed then we can say with 95% confidence that f lies between 0.05 and 1.0 -- In other words we are 95% sure that we are one of the last 95% of humans that will ever exist
n / N > 0.05 (with 95% confidence)
So:
N < 20n
By assuming three facts (1. 60 billion humans have been born up to today 2. The world population stabilizes at 10 billion 3. life expectency evens out at 80 years) we can say with 95% confidence that the total number of humans, N, will be less than 20·60 = 1200 billion and that that humanity will disappear within 9120 years.
Nearly everybody's first reaction to this argument is that there must be something wrong. Yet despite being subjected to intense scrutiny by a growing number of philosophers, no simple flaw in the argument has been identified.
Ho Hum.
Most of my discussion of the so called doomsday argument was lifted from Wikipedia, where it is detailed much more eloquently than I could manage on my own. A different description of the doomsday argument exists here along with a number of criticisms, loopholes and alternative interpretations
So I've Got This Axe, Right...
Let me illustrate this with an example from the fantastic internet novel John Dies at the End:
In short the question is 'what is the identity of the axe you are holding', is it the same axe as before? This question is derived from the well known Ship of Theseus
The naieve answer (and the one that I heard a bunch of people in the department give) is that of course it is a different axe; every single molecule in the axe has been completely replaced therefore it is a completely different object. This point of view is, however, missing something. A typical neuron in the brain will sit in it's own spot for your entire life but at any given time it's constituent atoms are being swapped around, added or removed. Is it the same neuron from day to day? Are you the same you from day to day? (this is discussed in passing here and here, and in a little more detail here)
This is something I have neither the time nor the expertise to discuss full here, but the wikipedia article on Identity and Change makes for a fine read and underlines exactly how bloody confusing this whole discussion is.
Originally there were to be four different topics in this post but I'm feeling far too tired to write in a coherent manner right now. Maybe some other time...
When creating my last post on just thinking about stuff I had a lot of fun and also stimulated quite a bit of interesting debate so I thought I'd do it again with a few more fun things to ponder:
Oh God! Oh God! We're All Going to Die
Not only are you going to die but everybody you know is going to die and in the end, every single human being that ever existed will be die. And then humanity will cease to exist.
Cheery, huh.
Well wouldn't it be nice to know how long we have before the whole of humanity dies out? One very compelling argument comes from Brandon Carter (incidentally the same guy who also introduced the anthropic principle) and goes as follows...
Consider the total number of human beings that ever have, or ever will, live (N), and our position in a chronological list of all humans that will exist (n). The fraction of human beings that were born before us is f=n/N
The Copernican principle suggests that since we are not special observers that n should be uniformly distributed between 0 and N. Let us further assume that our fractional position f is uniformly distributed between 0 and 1 even after we learn of our absolute position n. This is equivalent to the assumption that we have no prior information about the total number of humans, N.
If f is uniformly distributed then we can say with 95% confidence that f lies between 0.05 and 1.0 -- In other words we are 95% sure that we are one of the last 95% of humans that will ever exist
n / N > 0.05 (with 95% confidence)
So:
N < 20n
By assuming three facts (1. 60 billion humans have been born up to today 2. The world population stabilizes at 10 billion 3. life expectency evens out at 80 years) we can say with 95% confidence that the total number of humans, N, will be less than 20·60 = 1200 billion and that that humanity will disappear within 9120 years.
Nearly everybody's first reaction to this argument is that there must be something wrong. Yet despite being subjected to intense scrutiny by a growing number of philosophers, no simple flaw in the argument has been identified.
Ho Hum.
Most of my discussion of the so called doomsday argument was lifted from Wikipedia, where it is detailed much more eloquently than I could manage on my own. A different description of the doomsday argument exists here along with a number of criticisms, loopholes and alternative interpretations
So I've Got This Axe, Right...
Let me illustrate this with an example from the fantastic internet novel John Dies at the End:
Let's say you have an ax. The kind that you could use, in a pinch, to hack a man's head off. And let's say that very situation comes up and for some very solid reasons you behead a man. On the follow-through, though, the handle of the ax snaps in half in a spray of splinters. So the next day you take it to the ax store down the block and get a new handle, fabricating a story for the guy behind the counter and explaining away the reddish dark stains as barbecue sauce.
Now, that next spring you find in your garage a creature that looks like a cross-bred badger and anaconda. A badgerconda. And so you grab your trusty ax and chop off one of the beast's heads, but in the process the blade of the ax strikes the concrete floor and shatters. In short the question is 'what is the identity of the axe you are holding', is it the same axe as before? This question is derived from the well known Ship of Theseus
The naieve answer (and the one that I heard a bunch of people in the department give) is that of course it is a different axe; every single molecule in the axe has been completely replaced therefore it is a completely different object. This point of view is, however, missing something. A typical neuron in the brain will sit in it's own spot for your entire life but at any given time it's constituent atoms are being swapped around, added or removed. Is it the same neuron from day to day? Are you the same you from day to day? (this is discussed in passing here and here, and in a little more detail here)
This is something I have neither the time nor the expertise to discuss full here, but the wikipedia article on Identity and Change makes for a fine read and underlines exactly how bloody confusing this whole discussion is.
Originally there were to be four different topics in this post but I'm feeling far too tired to write in a coherent manner right now. Maybe some other time...
