Last night I found myself reading a paper on a futuristic propulsion system. It's been around for several years and manages to excite the tech beat websites every time. I'll spare you details, but it makes a rather dramatic claim. Extraordinary claims require extraordinary evidence. This wasn't it. It was peer reviewed, but I doubt by practicing physicists. The reported result was very small and several sources of error that could have easily swamped the result were not investigated. A standard technique known by any undergrad physics student was not used and there was evidence of cherry picking data. This doesn't mean an effect wasn't there, but it is likely they didn't really see it if it was. Their explanation of the effect was a bit on the cranky side, although you have to give them a pass on this part if everything else is in order. People want there to be magic, but Nature has her own playbook.
Without invoking magic of some kind they violate the conservation of momentum ... like sitting in your car, pushing on the steering wheel and having the car move down the road. Sort of wrong at the fundamental level. Conservation of momentum basically states the linear momentum of a system stays constant if the system isn't subjected to external forces. This is a really big deal.
Aristotle said to keep something moving you, or something, has to keep pushing. Push a plate of pumpkin pie across a table and it comes to a stop unless you keep pushing it. The same thing happens even with a hockey puck on the ice. It goes a good distance, but eventually comes to a stop It was directly observable and everyone bought it. Well -- almost everyone. Galileo came along and said wait... what if you imagine doing this in a perfect environment. One without air resistance or surface friction. In that case the plate of pie would just continue moving along in a straight line forever. It went against common intuition, but turned out to be right. More time goes by and Newton offers Newtonian physics. At it's core it's very simple. You do simple calculations and get the gist of the physics and then add in the effects of friction and air resistance. You reduce the problem down to its core and later bring back complexity. What we've found since then is this is how Nature works.
Galileo did more than a few brilliant things. The telescope was fine and fundamentally changed how we saw ourselves in the universe, but this notion of reducing a problem to an ideal situation and then understanding the rules obeyed by the individual bits in a similar way we bootstrap into understanding complex real-world systems. Modern physics was born. I consider this the most radical and important thought in the last thousand years ... perhaps even longer.1 All of science and technology is based on it.
One more thing...
The conservation of momentum has huge implications for how the Nature works - something a lot of people still have problems with. Aristotle talked about the natural state of things. The plate of pie was naturally at rest. Since some items moved there had to be a mover. Cause and effect .. he said everything happens for a reason. He bootstrapped back to the notion of a prime mover or first cause. But the conversation of momentum, and all of physics that follows, says the opposite. Things move because they are.. no reason is necessary. The relation between events is not one of cause and effect.
We still talk about causes and effects all the time and there are on the surface ... but reality is heavily layered. If you follow the thread all the way down .. in the case of the moving plate of pie, or the Earth orbiting the Sun it is easy, but if you keep going to the deepest levels and get to basics: spacetime, equations of motion, quantum fields and so on .. you find no causes lurking about.
Perhaps the most mysterious thing about Nature is that we can observe and work out how to understand it.
1 This is superhigh level. The notion of conservation of momentum slowly emerged in dribs and drabs for hundreds of years prior to Galileo's brilliant insight. He was an undeniable genius of the first order, but no one - not even the best - study Nature in isolation.
No recipe corner as many of us are currently over-indulging. Instead here's something about a neat number. I don't know if you have a favorite integer. Some friends tend to go for 17, 42, 47, 73 (paired with 37) and 137 for curious reasons. My taste is more catholic .. I like numbers in general. Here's something neat about 17 I realized a long time ago...
1/17 is the first reciprocal of a positive integer whose periodic decimal expansion contains all 10 digits. (1/17 = 0.0588235294117647 0588235294117647...)
42, of course, with a tip of the hat to Douglas Adams, but it is also the integer closest angle at which red light is bent into its position in a rainbow by a water droplet .. it is the rainbow angle.
folklore has it that 47 is the most likely integer given when someone is asked to name an integer between 1 and 100.
73 and 37... there is a rich connection which was picked up on the Big Bang Theory