Mr Monkeybat

The most energy efficient mode of travel is the gravity train 42 minutes from anywhere on Earth. But if you cannot build a friction free tunnel though the mantle a vactrain along the surface is just as efficient and faster if you have a perfect vacuum in your tunnel and efficient superconducting maglev track. All the energy put into the train to accelerate it, is recovered when you decelerate no matter how fast you go. In more realistic scenario's the slower the method of travel the more efficient it is as friction and air resistance increase exponentially with speed. But this can be offset by other things, when you divide a modern jetliners fuels consumption by the maximum number of passengers it has over 100 miles per gallon better than most cars at single occupancy.

Space elevator is just about posible with carbon nanotubes and graphene at their top strength. More feasible with current materials are Orbital Rings and Lofstrom Loops. Mass is accelerated above orbital velocity keeping the static structure with magnetic track suspended above the Earth by centripetal force. The mass driver 80km up in the vacuum of space accelerates the cargo and passengers up to orbital velocity. This is quicker and actually more energy efficient than the Space Elevator. I recommend Isaac Arthurs videos on the subject:

Something that could change earths orbit without necessarily destroying would be something like a interstellar planet like object or a brown dwarf passing through the solar system and close enough to Earth for its gravitational pull to significantly alter the Earths trajectory. Based on the fact that the eight planets all have fairly stable circular orbits this probably has not happened before and is unlikely to happen in the foreseeable future. When one object orbits another, it is falling, but missing the ground. Eventually in 4 billion years or so the Sun will grow into a red giant and possibly big enough for the Earth to get swallowed by the sun.

I had a fairly vivid dream in which I invented something. It was a hollow copper sphere, made out of 2 hemispheres clipped together 1 meter diameter just big enough for someone to crawl in and be locked inside. Attached to it was a 300 megahertz UHF radio transmitter, so the wavelength was the same as the diameter of the sphere. When someone was was locked inside and the transmitter turned on, being encapsulated in the quantum state of the standing radio wave photon amplified the effects of morphic fields restoring people bodies to there previous forms effectively rejuvenating and healing them, even giving them some mental control over there own genes. As the device was so easy to reverse engineer and copy in any handy mans garage and with demand so strong I ended up forgoing any intellectual property rights making it free to copy. Which is why I have described it here. I have had dreams that have come true before, so if you have those kinds of parts lying around in your garage it is worth a try In my dream I dont think anyone really understood how it really worked, phrases like "quantum entanglement", "morphic fields", "quantum uncertainty" where thrown around rather speculatively. Old people where shut in, the device was switched on for a few minutes, then then came out looking like 20 year olds which I thought was rather handy as I am already developing a bald spot myself, amputees got there limbs back. The subjects did not seem to be aware of any of the time that passed while the device was switched on.

If after somehow mastering interstellar travel, we came across planets that are like Earth with liquid oceans of water but devoid of life. How long do you think it would take after spreading some algae and plants for its atmosphere to become breathable for humans and other Earth animals. Wouldn't such a planet be much easier to colonize than a world with its own life forms.

The occasional land slide of other disaster does no stop large contiguous forests from developing or at least before humans stated felling them. When a land slide creates a bare patch in the forest does not stop them from quickl being filled in with plants and trees again. Xrays from Supernova only sterilize one side of the planets near them anyway. And it could be argued that the most likely form of interstellar species could be self manufacturing robots which can be largely immune to radiation.

I have not done that much research yet, it was just a thought I had the other day. My web searches for rectenna etc powered aircraft did not bring up many previous examples. But today I stumbled upon these people called Escape Dynamics working on a very similar idea. They dont mention using the atmosphere for reaction mass though and their website does not seem have the kind of details and figures that would satisfy Enthalpy, or me for that matter. http://escapedynamics.com/ http://singularityhub.com/2014/05/11/escape-dynamics-aims-to-eliminate-single-use-rockets-in-space-flight/

Perhaps I should parse my quotes more I was responding to this coment. Which I though was strange look outside a window plants grow wherever they can the areas where there are no treas are places where there is a shortage of water like the desert or where humans have removed them. In places where it is too cold like the tundra or too wet like the sea life more adapted to these environments than trees exist. You dont see exponential growth in nature that often precisely because it acts so quickly soon filling up an area so quickly that other limiting factors of the enviroment comes into play. But there are lots of examples of exponential growth when a species are introduced to a new habitat that they find useful, like rabbits and cane toads in Australia Reindeer on St Mathew Island, virus epidemics, humans entering new continents, and bacteria in petri dishes, or course when the bacteria reaches the edge of the petri dish resources become scarce for they cannot digest glass certain types of bacteria may start eating each over or poison themselves with their own waste products. Think of an interstellar species as a bacteria and the galaxy as a giant petri dish in space. The period of exponetial growth for an interstellar species would also be short in geological time a few thousand years or so soon the frontier will be to far from center for it to be available to the bulk of the population so the frontiers advance reaches a maximum speed. Or if there warp engines are very fast exponential growth can continue until the galaxy is full but the exponential period is still only a few thousand years long.. If the aliens where only looking for and living on planets like their home world then that would actually increase our chances of being in an overlooked part of the galaxy. But a species living in space habitats making use of all the resources of dead worlds and sterile space asteroids and debris could make for a very crowded galaxy indeed, and the galaxy looks more like a fertile dish of agar. Of course the question of how easy interstellar travel will be in the future is not settled I will accept that the galaxy could be full of sapient tool users that never leave their home world.

No I do not assert there will be no attrition in the grand scheme of things it makes no difference. Place like Europe and China have seen the rise and fall of different civilizations and the result is that every scrap of land is used and or covered with some or many archaeological layers. Every part of the earth that has liquid water and sunlight is covered by life trees and other plants are found wherever they can grow, or replaced by concrete. Artificial habitats make no difference you cannot fight the exponential function with size. I expect the limits of the available galactic resources to limit population growth long before I project the weight of human population to exceed all the galaxies stars in under 10,000 years time.

All life is subject to Darwinian evolution if alien life started spreading between stars a million years ago the galaxy would be full already every scrap of mineral resource consumed including the solar system. I am not going to accept simple appeals to the unknown before I throw away the rules Darwinian evolution and the exponential function. The future does not look like Star Trek either the galaxy is empty or interstellar travel is close to impossible. In the history of life on Earth a million years is small period of time its extremely unlikely that multiple species would have their technological revolutions within a few million years of each over forget about millenia or centuries. So appeals to the fact that Human would be pretty unobservable to aliens also is facile unless you think this is about as far as technology goes with the industrial age ending with the depletion of fossil fuels or something.

You cant appeal to the size of the galaxy like that Mordred if species creates colonies around other stars and they are able to sustain themselves they will have children and eventually create other colonies. A simple back of an envelope calculation shows that even with a really slow population growth rate doubling only once a century within 20 thousand years the collective weight of human body mass will be greater than the galaxy stars and all. So if like all life these Aliens reproduce exponentially when habitat is available all planets will be consumed later generations will not have the luxury of choosing any planet in the galaxy to colonize. If there was lots of planets with a biohistory similar to Earth the is no reason a species could not be where we are now in technology over a hundred million years ago. Even if first encounter was now if you have the tech to travel between stars you can also flatten every human city in minutes we would pose no military threat. If they have not invented good robots yet perhaps we could make useful slaves, maybe keep a few pets in zoos like we do.

Did you 2 read the whole post or just the title? The wikipedia definition of a rectenna is: "A rectenna is a rectifying antenna, a special type of antenna that is used to convert microwave energy into direct current electricity. They are used in wireless power transmission systems that transmit power by radio waves." So the power is any ground based power station via ordinary electricity pylons. And if it can reduce the cost of putting things into space enough Space based solar power transmitters. The idea of a space plane is to make getting from the surface of the Earth to orbit and back easier. For example the plan of Skylon has an "air breathing rocket engine" which makes use of atmospheric oxygen until it reaches mach 6 in the upper atmosphere when it switches to its own oxygen tanks which are smaller than if it had to rely on its tanks from ground level. Instead of using the oxygen I just want to use the atmosphere as reaction mass in a VASIMR type plasma engine until it reaches its top speed in the upper atmosphere when it switches to on board tanks, if you have a better term for this than "air breathing" I am all ears.

If your vision of the future is Humans or any other tool using lifeforms, has us never leaving the solar system, and never making the kind of high power trasmissions that would be detectable by SETI then indeed there is no Fermi's paradox. However if your brand of futurism involve colonising planets around other stars, or Von Nuemann probes, or any transmissions or space structures that will be visible from interstellar distance, then you must either question your vision of the future or suspect that life or more particularly hominid type tool users are so rare that humans will be the first to go interstellar in this galaxy.

I thought microwave focusing and beam forming was quite good these days.

Akbar thinks it should also have aplications in wireless power transmission. http://akbars.net/how-steve-perlmans-revolutionary-wireless-technology-works-and-why-its-a-bigger-deal-than-anyone-realizes.html#conclusion