Wtf?!?

[Steel General]

Looking at all those formulas gave me a headache.

[torstan]

So what's the point of this research? Well, firstly this isn't the primary research of this person so they didn't go to a funding body and ask for funding for this work. They have a position at a university and this is something they decided to use their time to think about. It's a good thing that people have freedom to choose a certain amount of their own research topics.

The second point is that this is actually quite important research from a particular point of view. It's to do with the anthropic principle. So first I'll see if I can cover what the anthropic principle is:

Consider the following. There are very few planets with atmospheres of oxygen and large bodies of water. There are very few planets with life (we only know of one). The chance of either is very low so the chance of both must be extremely low. Say for example that the odds of a planet having a breathable atmosphere were 1 in 10 and the odds of a planet having life was 1 in 10. Then the odds of finding a planet with both a breathable atmosphere and life would be 1 in 100?

The logic here is clearly wrong. Life requires a breathable atmosphere so the two are not independent statements. We don't spend a lot of time and money trying to figure out why we are on earth rather than Mars. We observe a planet with oxygen and water and a reasonable temperature because we need to have those conditions to exist in the first place. This is an example of a very rare observation (a planet with oxygen and water) that we don't need to worry about explaining. This is the anthropic principle. It says that there are some things that have to occur for us to exist and observe them. So the fact that we observe them is no surprise, no matter how rarely they might occur.

Now let's roll this back to physics. There are many things in physics that look to be very finely balanced. There are weird patterns and coincidences. So for example it was a strange coincidence that the number that determines how hard you are to push around (your inertial mass) was exactly the same as the number that determined how hard you are pulled towards the center of the earth (your gravitational mass). This coincidence turned out to be caused by a deep connection between gravity and acceleration that forms the basis of general relativity. So a seeming coincidence is explained by a deep underlying principle. Physics progresses by such steps. We see a coincidence and rather than accepting that it just happens to be the case that two numbers are the same, instead we ask why they are the same. We propose a law that relates them and then we test it. So if we see a coincidence, then we go looking for an underlying law.

How does this relate to the anthropic principle? To answer this we need to talk about a very bright guy called Weinberg. There's a number called the cosmological constant. It's a term in Einstein's field equations that sets out how fast the universe expands. Now it's pretty small, very small in fact. We also know that it's very unlikely indeed for it to be very small. In the early universe it should get big quickly - so it needs to start off almost unimaginably tiny to end up being the size it is today. There's no reason yet why that should have happened. This of course has lead to all sorts of theories about how the cosmological constant could arise from deeper principles that require it to be small. These are certainly valid avenues of research. However Weinberg proposed an alternative solution. He asked what would happen if the cosmological constant did what the theories say it should do. What if it starts off non-zero and then as the universe evolves it gets really large? In that case the universe expands enormously quickly, molecules don't form and large scale objects never exist. In that case observers wouldn't exist and there would be no-one to see the universe. So the cosmological constant has to be small for us to measure it.

Now to complete the argument you need one more thing. You need there to be lots of universes (as predicted by string theory). If you have lots of universes then you have lots of different cosmological constants. In some (very small) fraction of them, the cosmological constant is small enough to allow matter as we know it to form. Now only those universes will have the possibility of having observers in them. Therefore all observers must measure a small cosmological constant. Therefore there is no mystery as to why the constant is measured by us to be small. This is exactly parallel to the argument about why we see a planet around us with a breathable atmosphere. These unlikely circumstances are precisely required for us to exist - so we shouldn't be surprised when we observe them. Instead this is taken by some to be a validation of string theory and its prediction of many (10^1000) different universes that all have different values for the physical constants such as the cosmological constant. Now I'd say that's overstretching things more than a little, but that's the argument.

Okay, so what does this have to do with giraffes?

Well, the argument in that paper derives the height of the giraffe in terms of the proton mass and the ratio of the strength of forces. At the end of the paper he runs the argument in reverse. Say we take our observations of large scale molecular life and ask what this requires the fundamental constants of physics to be. Then he claims that we can pin down many of the fundamental parameters. If they were other than that, then large scale life could not exist. If we couple this with string theories roulette ball of universes where these numbers are different in every universe, only those universes where all these numbers take values in these ranges can accommodate large scale observers like ourselves. An advocate of the anthropic principle would then say that there's no point in looking for a deeper understanding of the root of these values - instead just accept that they are the toss of the dice required for us to measure them.

In my opinion, this is certainly an interesting argument. It's important to have a good idea of what is and is not required for use to exist. For example, some people have tried to claim that the current measurement of the amount of dark matter can be explained by the anthropic principle - but it's not required for the existence of stars, galaxies and planets so there's no way we can explain that number away on these grounds. Therefore it clearly tells us that we should look for a deeper understanding of the dark matter density. However I'd also say that we shouldn't discard a question just because there might be an anthropic explanation. Yes, the cosmological constant might be the way it is due to pure chance. However there may still be a deeper explanation, and if we solve that then we will gain a vastly improved understanding of the fundamental force that drives the evolution of the universe, how it began and how it might end.

So I think that the research into the connection between the height of a giraffe and the mass of a proton is very relevant to what questions we can and should ask in physics but I don't agree with the anthropic principle or the multi-universe explanation due to string theory that it relates to. I hope that helps a little with the context? Throw me any questions you have about it and I'll see if I can answer them.