Carrock

My first thought .... Seems like a Wankel engine to me. In http://www.gizmag.com/duke-engines-axial/33631/

The ESA paper does not describe that or alternative optical focussing. As there is a laser at each star power from each laser is only required for half the distance. Any calculation of power etc would require an enormous number of assumptions and a few billion/trillion dollars to verify them. There may be a few billion dollars' worth of relevant classified "Star Wars" research. Which part of "With a lot of work ....." did you not understand? This is my last post in this topic.

One of the things I've always liked about U.S. patent law it that it doesn't refuse to accept perpetual motion machine patents. A working machine is required though. I generally accept authoritative pronouncements on the laws of physics until someone more impressive comes along.

A lot of proof of concept work has been done on this eg http://www.esa.int/gsp/ACT/doc/POW/ACT-RPR-NRG-2009-SPS-ICSOS-concepts-for-laser-WPT.pdf and http://www.academia.edu/4135938/Laser_Starways_light_bridges_to_the_closest_stars

With a lot of work ..... The power would depend on how much acceleration the passengers wanted. And of course I'd have to guess the minimum practical mass per unit area of the sail to see how big it could be. It couldn't usefully mass more than about half the payload. With onboard fuel, you first have to accelerate all the deceleration fuel up to maximum speed.

High energy lasers focussed over interstellar distances on a spacecraft's light sail to accelerate it are a reasonable extrapolation of current technology. With one at each end of the journey efficiency would be much better than any onboard fuel.

I wasn't really demanding evidence, just trying to make a point about the limitations of knowledge without getting too serious. I've thought better of claiming that there is no evidence that anyone in government has ever committed an undetected crime.

Indeed. There is no evidence that any government has ever succeeded in keeping anything completely secret.

Your post explains everything except why they bothered to come. Perhaps they are much like juveniles throwing stones at a hornets nest. If we succeed in stinging them their parents will come along and humanely destroy the nest.

Sorry - I meant to say isospin monatomic hydrogen, where the atoms don't combine into dihydrogen unless a few atoms' spins are flipped. The energy of reaction is enough to flip more spins for a runaway reaction. I believe there is at least a 0.01% probabilty of this fuel being used in the next hundred years.

It's possible that most ETs have calculated that sending out, say, a terawatt of 'I am here' signals for a million years would give them a 50% chance of contacting one other ET civilisation. They may not be advanced enough to take the long view.

Spin polarized monatomic hydrogen has been the rocket fuel of the future since at least the 1950s. I don't know the specific impulse but it is pretty high. It's nowhere near as easy to handle as nitroglycerine and it requires a liquid helium plated fuel tank as it reacts explosively with anything else. There are a few more similarly trivial problems to overcome before it comes into use.

There's actually a lot of practical value on the moon. There's water that can be electrolysed for rocket fuel and at least most of what you'd need to manufacture spacecraft. Only about 3% or less of the energy required to launch an interplanetary spacecraft from earth is required to launch it from the moon. You could even build a linear accelerator to launch spacecraft using only electric power from ( a large number of ) solar panels. Of course all this would require an enormous investment before there was any payback. Science fiction would be pretty dull if authors ran their ideas past an economist.....

It's not at all clear how long inflation continued ( perhaps far longer than the minimum required to fit observations ), but at the end of inflation the (now) observable universe was certainly very small. However it seems likely a much larger volume at that time was very similar to what we can see - no edge effects have been detected. It could easily have been more than 30 billion light years in diameter back then. Enough to qualify as a big bang?