mistermack

It's a false premise, though, isn't it? If you give an opinion that something is worthless, it doesn't follow that you are saying it will never be worth anything. Your example of Alaska is a bad one. It wasn't a case of not knowing all the facts. It was a case of not knowing the future. And that applies to everyone equally. The people who sold Alaska were dead before the place became worth anything. And they were concerned with the present, not the chance that someone might strike gold thirty years later. Similarly, Mars IS worthless today. Nothing that's there can possibly be worth the cost of getting it. Today. If you go back and look, you will see that I wrote in the present tense. The notion that it will NEVER be worth anything came out of your own head, not what I wrote. Mars is of academic interest right now. The Moon could actually prove useful.

I don't really understand what that means. From memory, if I held a spinning gyroscope in my hands, it resisted being turned to the left, and to the right, equally. So I was imagining that two parallel ones would just double the resistance to turning.

The fine accuracy that you long for does you great credit. I can rest easy. The future of Mars is safe in your hands. It's true that there must be abundant resources on Mars. But using them will be difficult. It's costly to get there, and costly to get off. On a huge scale. And colonies can't really be independent, unless you can produce the next generation. Nobody knows what a fetus, or young child, will grow like, in gravity that is less than one g. And I have my doubts that any moral society would choose to experiment by bringing up children on Mars. Maybe, after several generations of apes had been produced on Mars, with no adverse developmental effects, they might think it safe and moral to bring up a child there. It would all take hundreds of years to achieve.

Most speculation is of a premature nature. It's academic. You'll be dead before they find out. And so will I.

Once you've cracked the problem of sustaining the plasma, you have to crack the materials problem, of making hardware than can handle the high energy particles that are emitted. Until you can run the reactor for serious intervals of time, you are guessing what will happen to the surrounding materials. As soon as ITER is running at serious power levels, the problems of maintaining the hardware kick in, and they might be deal breakers. Or not. Of course, there are other projects on the go. They might achieve a surprise breakthrough before 2026.You never know, but it doesn't look likely. Maybe solar energy will get there first, with cheap reliable energy on tap. If they can develop efficient storage, that could happen.

I have to say that light IS heavy. If you define heavy as something that responds to gravity. In a black hole, photons are too heavy to escape.

I believe that they can maintain fusion for well over a minute now, and records are being broken all the time. That's with the existing machinery, but once the giant ITER project gets going, they should be into a different scale of fusion. It now looks like the first plasma from that will be produced in ten years time. Shame they can't get their act together, and move it on a bit quicker. I'm sure that fusion will be the answer to fossil fuel problems in the long run. Maybe when ITER is pushing out power, the real investment will start, and things well really speed up.

Not every gamble pays off. You win some, you lose some. Any lottery winner would tell you it's a great bet. But is it? There might be stuff on Mars that makes it all worthwhile. There might not. With Mars, it's not a question of "do we do this, or don't we?". It's more a question of, what is the BEST project to put your billions into. Mars, the Moon, giant space stations, comets, near Earth objects? You can't have it all. Right now, I would say the Moon would be the best bet.

Well, I'm no expert, but from what I've read, a flywheel tries to maintain the direction of it's axis, and that would apply for both flywheels in the same way. So it's resistance to change, not directional, I think. I would imagine that it would be best to mount it vertically, as you don't meet many steep slopes, so that axis would be the most stable. I don't know how acceleration and braking would affect the flywheel though, although I'm betting that it's been tried and there is info online.

The thing is with a flywheel, that the energy density isn't critical for all applications. So you don't always have to be using such high speeds, or expensive materials. I don't think that flywheels will ever be suitable for road vehicles, because of the forces involved if you change direction. Maybe on a straight railway track or a ship you could get away with one. They are most suitable for static installations, and in those instances, energy density isn't so critical because weight doesn't matter so much.. Instead of spinning it so fast that you need exotic materials, you just use lower speeds and a bigger flywheel. The main cost comes in building and maintaining a safe and efficient housing and bearing. I think that batteries will remain the best alternative to fossil fuel for road vehicles, unless capacitor technology can overtake them. Edit : I clicked on the link about carbon nanotubes, and I think they are talking about using them as some sort of superior spring, which has a much higher strength to weight ratio and greater durability than current spring materials. Maybe that could be installed in vehicles, in some way, and you just pay at stations to have your spring wound up? It might have safety implications though, if something breaks.

That would be nice, to find all of that floating around, ready to use. There certainly are plenty of near Earth objects out there. Wikipedia has a big page on them. https://en.wikipedia.org/wiki/Near-Earth_object When they say "near Earth" though, they are often talking about things that are huge distances away, or have a Solar orbit that is only rarely in the vicinity of Earth. I believe that comets are the best bet, for water ice. There are about 100 classed as near-Earth objects, although they are probably rarely anywhere near Earth. Maybe the ideal find would be broken bits of a comet, small enough to actually be able to capture and use. I wouldn't discount the Moon though, as a source of raw materials. Yes, it has a gravity well, but it's tiny compared to that of the Earth. And the complete lack of weather and low gravity on the Moon means that you could build a tower to a phenomenal height, and possibly accelerate objects straight into orbit using mostly electrical power, which would be fairly abundant on the Moon, once you got Solar Arrays going.

I don't think it's likely that it will ever be practical to build something like that on Mars. Or sensible even. It would be all so much easier on a space station. No gravity, so no bearings needed. No atmosphere, so no energy losses and very little control needed. Mars is totally unattractive as a place to live, or use. It's gravity well and lack of atmosphere make it worse than the Earth for most practical purposes. The only thing of interest about Mars is whether it has fossil life, or frozen remnants of life. It's Moons might turn out to be useful though.

There was a thread in February about this : http://www.scienceforums.net/topic/103508-solid-state-battery-announced/?hl=goodenough

I doubt Mars gravity would be enough for people to live on permanently. Maybe older people could survive in good health for years, but I doubt if children would develop normally without one g gravity, no matter what exercise routines you put them through. In any case, to give Mars an Earth-like atmosphere would take a gigantic amount of nitrogen and oxygen, and it would probably be swept away by the solar wind as fast as you could produce it. And I don't think (I haven't checked) that Mars has a magnetic field to match that of Earth, so even with an atmosphere, life will be exposed to higher levels of harmful rays from the Sun. I'm pretty sure that the only way to make it habitable would be under dome-type structures, and they would have to be pretty special, to have I atmosphere of pressure inside, and nearly zero outside. I think that would restrict their possible size down to a small level.

I agree the cost is staggering, but, only in the short run. In the long run, once you are getting your raw materials from places other than Earth or Mars, such as the Moon, then the costs will drop dramatically. In space, energy costs will be very low, and space to live and expand is unlimited. And transport in space will be cheap. So once we master living in space, and living OFF space, in the very long run, it will be cheaper and better. I don't think that Terraforming planets can compete with building giant space stations. Unless you can find a planet with about 1g of gravity. Space stations have all the advantages.

Well, without doing any research, I believe that collisions at very high speeds generate Xrays which can be harmful to health and equipment. So if the shield is a significant distance ahead, this could be minimised. You would have to arrive at a best compromise, between distance ahead, and efficiency of shielding. I don't think that detecting obstacles would be doable in practice. At very high speeds, you would have to detect them a very long way ahead, and that would be pretty much impossible for dust-sized particles.

It's interesting to think about how you can shield against collisions. If you have a shield at the front, clearing the way, you can site it quite far ahead of the rest of the craft. Of course, if the particle has lateral movement relative to your direction of travel, it can miss the shield, but still hit the craft. But the faster you are travelling, the less likely this is to happen. So if you are travelling at a significant proportion of c, your shield should be clearing virtually all dust particles. I don't know about the motion of the hydrogen atoms that are floating in intergalactic space, but I'm guessing that they haven't got much energy, so they are not very likely to miss the shield either. You would have to work out the best compromise, for how far in front of the main craft you would put the shield. But the faster you are going, the further in front you can put it.

It's interesting that the dust in the galaxy blocks out light from 6,000 light years away. Of course, that's side-on to the Milky Way, in the plane of it's disc, so it's not too surprising. If you compare that to the light I mentioned coming to Hubble from the farthest galaxy yet detected, then that light has travelled about two million times farther, without being blocked out. Which illustrates the point that intergalactic space is much less likely to have a particle of dust in the way. It's actually confusing how the various sites refer to the space between galaxies, and the space inside galaxies. The term "intergalactic space" generally refers to the space between galaxies, but the term "intergalactic medium" seems to be used for the space INSIDE galaxies rather than between them. I would have thought that intergalactic should always refer to the space between galaxies, and just galactic medium for inside. The figures that I've seen, for particle density in and outside of galaxies, are that galaxies are about a million times denser. The space between galaxies contains about one hydrogyen atom, per cubic metre, and inside galaxies, it's about one hydrogen atom per cc. If dust particles follow the same pattern, then that explains why the Milky Way is so much more opaque, looking towards the centre. Of course, looking side on through the disc gives maximum opacity. I think it give a rough guide, that you are a million times more likely to hit dust inside a galaxy, than between galaxies, which isn't really surprising, since dust is the result of exploding stars, and isn't very likely to leave the gravity of the galaxy.

Meteors hitting the Earth are from the Solar System, which is much more likely to have comet trails etc than the space between galaxies. And the Earth is a big target with strong gravity. If you think of the most distant stars that Hubble can get an image of, then that light hitting Hubble has travelled for 13.8 billion years, obviously at the speed of light, without all of it being deflected, and still clear enough to form an image. And a constant image that persists, not just a flash in the pan. So those photons have travelled all that time at c and never hit a particle of dust.

Well, intergalactic space is far more empty than galaxies. If galaxies with billions of stars can pass right through each other without any stars colliding, then your chances of hitting something like a pebble or even a grain of sand in intergalactic space are an order of magnitude smaller.

I've seen it said that two galaxies could and probably would "collide", without one single collision between stars. Such is the distance between them. If that's the case inside galaxies, there's probably very close to zero chance of a collision in intergalactic space.

I recommend that you read up on Chimp behaviour. It's extremely complicated, and words like bully don't really apply in the same way. They have a dominance structure, and in that, you give way to some, and dominate others. But it's not simple. Just as human relationships are not simple. At the top though, there is usually an alpha male who dominates not just by fighting ability, but by political means, enlisting allies and commanding loyalty. And females present their hindquarters to dominant males, as a gesture of submission. You can't call it rape, in the human sense.

If time is a characteristic of change, then it seems to me that time can have local character, and universal character. Say for example, that it was physically possible for events for a very simple particle to exactly reverse what had gone before, then you could claim that for that particle, time had gone backwards. Or if nothing happens to it, maybe you could say that time stalled. But, if the rest of the Universe had moved on, as normal, then could you really make the case for any of that? Really, you constantly undergo change, relative to the rest of the Universe. Even if you don't undergo any change yourself. If every gravitational field extends to infinity, then the field that each individual is in is in a constant state of change. Even if it's minimal. So time of the Universe is ticking onwards, even if you "freeze" or reverse.

Reading a little more, it's an interesting concept. What approaches infinite largeness, is the relativistic mass. The rest mass doesn't alter one way or the other. The relativistic mass is an expression of the momentum and energy of an object in motion. It's different in every inertial frame. So if your chosen inertial frame is close to the speed of light, relative to an electron, then the electron will have approaching infinite relativistic mass. Einstein didn't like the concept of relativistic mass. As late as 1948 he wrote that it was better to use the expressions for momentum and energy than use relativistic mass.

If an object emits a photon, it loses mass. So that part of it's mass has become light. I agree that an object can't become like light by moving at c. But neither can it be accelerated to c, and infinite mass. Both are impossible cases. For something with mass to move at c, something impossible has to happen. That was how I was trying to put it.