When LHC was about to be launched there were many fears that it would destroy the world. To counter them scientists tried to carefully examine all possibilities and concluded that there is nothing dangerous. While most of their arguments sounds fine and reasonable to me there is one which I never understood. It is mentioned in many places, and here are some examples of it:
we can conclude that the existence of our solar system proves that mini black holes can not be dangerous.
If we ignore these strong theoretical arguments, we could pursue another path. Huge numbers of high-energy cosmic rays have hit the earth over its lifetime. Thus, we can argue, nature has already carried out the LHC experiments many times. If we are still here, the LHC must be safe. This is a standard argument that was worked out carefully by Jaffe et al.
It has always been reassuring that higher-energy cosmic rays have been bombarding the Earth since its creation with no disastrous side-effects.
This report explains why there is nothing to fear from particles created at the LHC. In fact, collisions just like those the LHC will make have been produced by cosmic rays bombarding the earth throughout its existence. It would take about 100,000 LHC experiments to match the number of cosmic ray events that have already occurred. We can rest assured that our planet will not be affected by the four experiments about to be conducted in Geneva.
So, basically, from those two facts:
- For billion of years events similar to those at LHC were happening on Earth.
- Earth still exists.
We are concluding that:
- If we will recreate these events at LHC Earth will still exist.
In my opinion (3) does not follow from (1) and (2).
Imagine the following scenario: out of all planets with life, 99% are destroyed by some events caused by cosmic rays before the appearance of scientists on these planets who will conduct experiments at particle accelerators. However, at 1% of lucky planets evolution will have enough time to create curious scientists who will build particle accelerators. Scientists on these planets will then argue that it is safe because their planet still exists. But on 99% of planets there is no one to argue. Sounds like survival bias.
If you are asking why conditions on our planet are comfortable for life, the answer is obvious - because there is no one to ask such questions on planets which are not comfortable for life, so if you are asking one you must be on a proper planet.
If you are asking why our planet was not destroyed by some hypothetical cosmic ray event, the answer should be - because on planets destroyed by such events there is no one to ask, it shouldn't be - because such events are impossible.
So, using billions of years of Earth existence as an argument is wrong. Instead you can use existence of other bodies (which do not affect existence of life on Earth) as an argument.
What do you think, is this correct?