Sonic Boom

It is widely known that a sonic boom is created when an object passes the sound barrier. But what many don't realise is the boom is continueous for as long as the object is supersonic, not just when the sound barrier is first broken.

Take a supersonic plane. This plane is in a 'soup' of particles which we call air, (air is actually more like soup than just a few particles whizzing around, which is what is taught in schools :/ ). As the plane moves through the air, the soup of particles at the front move out the way. The faster the plane travels, the faster the particles have to move out the way. But the particles can only move at around 340 metres per second and stay happy, which is why sound can only move at that speed, since sound it is simply particles moving.

So the most a plane can move and keep the particles happy is around 340 m/s. At this speed, the particles start to build up at the front of the plane, since they can't move away fast enough. For the plane to go faster, it needs to pierce through this build up. Planes with normal wings and tail would at this point have their rudders and flaps jammed due to the immense force now being emitted by the particles trying to hold back the plane.

This is why supersonic planes are extremely streamline, and why in early designs, instead of just some flaps and rudders moving, the entire wing and tail move. This prevents jamming as there are no flaps to jam.

The sound it created when this 'barrier' is broken through and the particles are forced to move out the way at a speed that is faster than what they're comfortable with.

Now that the plane has pierced the sound barrier, it needs to continue to pierce it because particles are still there up front. This produces a continues sonic boom, which is heard as long as the plane is supersonic speed.

The Concord only went supersonic over the sea for this reason, otherwise any windows that were in the flight path were likely to be smashed.

The Great Wall of China

It is often said that the Great Wall of China can be seen from the moon. Not only that, but it is the only man made object that can be seen. 

In fact, it can't be seen. There is no single man made object that can be seen from the moon. Continents, let alone countries, are only just about distinguishable. 

The only man made things that can be seen, as a collective, are lights. You my have seen images of the Earth taken at night; if you haven't, then google it - it is really impressive. You can still make out the continents but that is only because of the outline the lights create. If the lights weren't there, then you wouldn't be able to see anything on the Earth.

So if aliens were to pass by the daylight side of Earth, even at a distance much closer than the moon, and had no way of picking up radio signals, then they would pass by us, completely unaware of our existence.

Evolution - Mutation

Most people will realise that a huge part of evolution is mutation. But it comes with a lot of misconceptions attached.

A person may say the environment changes, then a mutation takes place to make sure the organism can survive in the new environment. Simple right? Yes, but this isn't what happens.

In reality what happens is this: random mutations are happening inside the animal all the time, then the environment changes, then all the animals which just so happen to have the right features at the right time survive.

So how do these random mutations happen? Is there some cosmological mandate which tells the DNA to change every so often? No, the answer is much simpler.

You may think your body is a finely tuned orchestra - with every instrument playing the right note at the right time, with the right dynamics etc. The real truth is your body is pretty bad at what it does, especially when it comes to replicating your DNA. I won't go into how it gets replicated but basically 80% of the time it does it wrong and has to start over again. All this incorrect DNA is just then stored in the cell, doing nothing.

 However, from time to time, the incorrect DNA is still readable. Since your cells don't have a conscience to say 'I'll only use the DNA I know is correct for this body,' it takes any DNA that is going, including the incorrect ones. So you're cell takes the incorrect DNA and processes it, and follows the instruction encoded in it. This is what leads to the mutation. It can be good, bad, or most of the time it just goes unnoticed. Simple.

These mutations are then passed onto the animal's young and their young and so on. Then comes a change in the environment. Only the descendants with the certain mutation can survive. The rest die out. That is natural selection. 

Climate Change

There is no doubt about it, the weather is changing. Why? Whether you like it or not, it is due to climate change. The doubt which does surround this topic is the contribution humans have given to the change.

Here are some percentages which might help put human contributions into perspective: 

 -  Humans contribute just 1 - 5.25% of all global annual CO2 emissions. (The range is due to the fact that it is difficult to measure the CO2 released in some processes, the 1% being the lowest estimate, and the 5.25% being the highest estimate). 

 -  Humans contribute just 0.28% of all global annual green house gas emissions.

So basically humans contribute a tiny tiny drop to the tsunami of global warming. All the natural emissions include trees naturally dying, volcanoes erupting, and yes, cows releasing gas, amount other things.

What does this have to do with our everyday life then? Well it means that even if humans stopped all contributions towards green house gasses, then 99.72% of current emissions will still be produced. So global warming will still continue. Unfortunately there is no stopping it. The truth is if your grandchildren don't go through it, your other descendants will.

However I'm not telling you to leave your tellies and lights and heating on, or taking unnecessary journeys in the car. All these things cost money, so being green will still save you money even if it doesn't save the world.

What will happen after global warming eventually 'destroys' the Earth? Believe it or not, most life will survive the natural cycle of the Earth, just as most life forms have done in the last cycle, and the one before that, and the one before that, and so on. The Earth will not become a inhospitable ball of freezing cold or scorching heat - this will only happen in some parts. The freezing cold mostly being in the northern part of the northern hemisphere and the scorching heat mostly at the equator, which leaves plenty of land for humans and other beings to survive. Then after a few hundred years, the cycle will start over again. Maybe in 10,000 years humans will once again be obsessing over their contributions to an effect they have no control over.