Frankly, Im a little haunted by the idea that unlike what we have found to be the case in the past our knowledge of physics may be fairly complete.Let me clarify this a little.I maybe fairly complete in so far as things on the human scale are concerned.If as I mentioned above Baryon conservation holds (save for the early universe or black hole collapse) the fusion is the ultimate energy source.This would give about a 0.35 percent conversion of mass to energy (CAT D-D).This would for practical purposes limit space travel not just to below the speed of light but very much below the speed of light.Wed be doing good to get to 1000 miles per second peak speed (round trip scenario).Conservation of momentum seems to always hold eliminating the possibility of a reactionless space drive. Interplanetary travel is very possible with this and we might be able to mine the asteroids, etc.But, the limits are perhaps a lot more imposing that is the general view of science fiction.
Id really like to prove the last paragraph wrong!
The great scientist Lord Kelvin was famous for saying that, There is nothing new to be discovered in physics now. All that remains is more and more precise measurement.Except he noted that there were two "dark clouds" cloud on the horizon, i.e. the unsatisfactory explanations that the physics of the time could give for two phenomena: the Michelson-Morley Experiment and black-body radiation.It has been noted that although the thrust of his statement was wrong he sure picked his clouds well!So it has become dangerous to predict the slowing of progress. However, we have been in a period of rapid progress in last couple of centuries that we have come to think this is the normal situation.But, in the history of the world it really isnt.This sort of progress usually has an S-curve shape and we should expect a plateau effect at some point.The question is when that will be?It could be in the near future or it could be in the world of Star Trek and beyond.
I too have my suspicions about the validity of baryon conservation--while it holds pretty well, there is something about it that doesn't seem 'right' when it comes to blackholes, especially evaportating blackholes, and more specifically tiny evaportating black holes...
I suspect that tiny blackholes may not conserve baryon number at all--and if that is the case then there exists the possibility of exploiting this feature to our benefit. A black hole made of 1 solar mass of peanut butter will have exactly the same properties, all other things being equal, as a black hole made of neutronium...the only properties that a black hole seems to have are mass, charge and spin. No other numbers seem to be concerved...
Hawking radiation, the mechanism by which blackholes are thought to lose mass, is a function of the entropy of a black hole, which is itself a function of the surface area...since Hawking evaporation is an effect of the quantum vacuum, it is plausible that a non-charged blackhole will have the same propensity to swallow positively charged virtual-particles as negative ones--thus we can expect a non-charged blackhole's event horizon to emit just as many matter particles as antimatter particles, and more electrons and positrons than baryons anyways because of their lower rest mass (and less internal complexity)...
This is why I conclude that if it should be possible to create a micro blackhole and force feed it some ordinary matter (such as in the collision of massive nucleii in a particle accelerator,) it should look for the most part like a shower of mostly electrons and positrons with no real 'pair linkages,' i.e., no or low momentum connections between them (they will not look like true pair productions.) Depending on the energies involved, a blackhole "factory" could swallow enough matter to power the whole shootin--match. This is conceptually the fabled 'mass converter' oft mentioned in science fiction: the mythical device that can 'burn' ordinary matter into pure energy. If such a device were possible, and relatively compact (light weight) then it is entirely conceivable that some kind of propulsion system could be built around it. Even if a propulsion system were not possible, the ability to liberate energy from ordinary matter without resorting to fission or fusion should be a step in the right direction to giving humanity all the clean energy it needs for the future and for all time...
And I think that goal is worthy of detailed study; I think it is attainable. If such a device were possible, then physics would not be dead--it would be the enabler of our species' survival!
Baryon conservation seems to be a broken symmetry. This is an interaction in the many of the grand unified model that has a very low frequency of proton decay. Black holes are the other possibility which destroys everything except mass, charge, and angular momentum. My point is that we have little access to either phenomenon so for us we can see baryon conservation as an absolute law leaving fusion as our ultimate theoretical energy source.
You suggest an interesting possibility that we could create a small black hole and feed it in order to maintain a stable mass as Hawking radiation emits energy to balance the mass inflow. There is a string theory prediction that high energy particle accelerators, e.g. the new CERN machine, can create a small black hole. This is one version of string theory starting with assumption the strings can be much longer that in the traditional view. If this turns out to produce something we would have new physics. But, these Kaluza-Klein resonances (micro-black holes) are vary short lived. There is no real reason to expect we can capture and maintain one of these.
If you could make one, however, what you would need to do is to put a net charge on it so that you could handle it with electromagnetic fields. One other problem would be when you tried to feed it more matter the Hawking radiation would tend to blow it away from the event horizon. The time to evaporation (err, explosion) is t ~ 3.94 * 10^-16 * M^3. If your micro black hole weighs 1 kilogram then we get t ~ 3.94 * 10^-16 * 10 ^9 = 3.94 * 10 -16 sec. This thing is very unstable and if you lose control you have 1 kg doing the E=MC^2 thing. People are worried about nuclear reactors, lol.
Ive give you credit that you have found a crack...well a small crack in my argument.
Well, the idea I had was to utilize the black holes evaporation as a power source--so you let it evaporate completely...you let the thing blow up. And then you make another one...
So you will need a 'black hole factory' so you can produce an endless string of them--each only lasting for a brief fraction of a microsecond. Under these circumstances, the energy produced in the evaporation process ought to approach the theoretical limit: E=mc^2; plus whatever energy went into the initial formation of the black hole, which is substantial.
If we could produce something with a mass on the order of a microgram, and produce them at the rate of 100 per second, the net mass conversion rate should be somewhere in the neighborhood of: 100 microgram per second: translating this to kilograms: mdot=100*10^-9 kg/s
Letting c=299792458 m/s, then differentiating E=mc^2 with respect to time and substituting gives:
P=mdot*c^2 = 8.989 * 10^9 Watts which is on par with the the thermal output for a nuclear power plant producing about 2500 MW of electricity!
By operating in a pulse mode, you don't have to keep a billion metric ton monster lurking in somebody's backyard...
The concept depends of course on a couple of caveates: 1) black holes behave the way we think they will behave: They evaporate according to Hawking Radiation Law. 2) black holes behave the way we think they behave: They don't leave any dense, non-reduceable 'information kernel' behind. They radiate all information contained within them. 3) We can force feed one a bit of mass before it evaporates: which means we have to transfer mass to it at a greater rate than is lost by the little beastie: and this means that for a brief instant, we have to cram mass into it at a rate approaching the total luminosity of all stars in the observable universe. That last part might be a little bit of a challenge!
Other than that, if we can do it, then pretty much everything else will look very similar to a conventional nuclear reactor: you'll need an gamma-ray energy capture medium: a cylinder filled with a thousand metric tons of softball sized tungsten balls ought to do nicely. Blow helium through the reactor in a closed Brayton cycle conversion system at 150 atmospheres of pressure and you've got the makings of a very clean powerplant that uses ordinary matter as its ultimate fuel.
I don't know if that's the way to do it. You need an accelerator as powerful as the CERN LHC at each reactor site to generate the micro black holes and to inject them with a microgram of mass. This seems doubtful...to be kind. I'd bet on the fusion reactors to be more likely to be sucessful. I don't see how one could use that version for space propulsion.
Now if you do it the way I'm suggesting, i.e. putting a charge on it with a proton beam maybe we could capture it and keep feeding it in order to maintain a continuous energy source. I really have my doubts but it does look like a fun problem to investigate. All of this is based on very optimistic assumptions about String Theory. You are right that gravity can break baryon conservation but you see the problems with making it a practical energy source.
But getting back to my main point which is that progress in basic physics may be experiencing a plateau effect. This doesn't mean no more progress but what progress we have will be out of the range of practicality. We may learn more about very high energy particles or the early universe. But this isn't going to give us anything that will make interstellar travel possible. (Unless you are talking multigenerational ships.) Here I'm very open to find a solution to controlled fusion, etc. as part of known physics. I don't think that fusion will require anything that isn't covered by Maxwell's Equations, Quantum Mechanics, and Special Relativity in some combination.
I think there is exceptional physics out there to be discovered, but yes, it'll be hard to get at. I suspect that there is remarkably much that can be learned from the quantum vacuum and process theory in particular which seems to indicate that space-time and its apparent 4-D nature comes about rather naturally and automatically from the chaos that exists at the Plank Scale...so I don't know if strings exist--perhaps they do.
I suspect that if something simpler can result in the rich complexity that we see and know about--then Occam's Razor suggests that that is the way to seek truth...
And that's why I love physics--so much of what we think we know could be changed by what we don't yet know.
For instance--take chemical catalysts: chemists don't really know why they work, because they don't really know how they work. Physics may provide some answers: local modification of the virtual energy density of the quantum vacuum; i.e., depressing the 'zero [energy] point' availabe to a chemical reaction momentairly increases the energy available for the reaction; increased energy density and lower initial energy conditions naturally increase the rate of reactions such as oxidation: once the reaction products leave the zone of 'lower zero point energy' they return to 'normal.' This seems to be the essence of how a catalyst works--even enzymes in ourselves...
And understanding the physics of that one thing can open up many new avenues for us.
I love physics too.But, I do have very serious doubts if what is happening on the cutting edge is going to lead to any technologies.It will lead to knowledge.It can lead to understanding the processes that occur in the early universe or what happens in the creation an evaporation of black holes. Understanding process that is causing the acceleration of the universal expansion or dark matter are other things we will learn. Im sure there will be additional surprises that we cant guess.Im eager to learn these things for knowledges sake if that all it turn out to be.(It would be great if it led a warp drive too!)
I would also like to point out that the basic physics (depending on how you define that) upon which our technology is based has changed little since about 1940.The latter was the discovery of nuclear fission.There has been a lot refinement and application of these discoveries but the applied physics/technology is consistent with what we knew by 1930.
I could easily see another 100 or 200 years of technology growth coming from this base of knowledge.
At the end of this fusion will still be the ultimate energy source, the speed of light will still be the ultimate speed, etc.There can be quantum computers that will leave our best looking like a 1980 Apple II or worse. There will be awe inspiring genetic technologies.Controlled nuclear fusion will solve the energy crisis, etc.We can make spacecraft that can roam the Solar System at will with this physics.So please understand Im not talking about an end of progress (at least not in the near term).
Something happened in the 20th century.We discovered the absolute scale of things.Planks constant is the fundamental unit of action.All actions are an integer multiple of this value.Previously we could wonder what the smallest action could be or even with there was such a thing.Now we have found it.The same thing goes for electric charge and angular momentum.We know have general very of the finite age of the universe and its general structure in a way that we simply didnt before.
This is where I get to the S-curve process.We make very slow process until we discovered the scientific method.Then it took off and the last couple of centuries have been the rapid exploitation of it. I think we are now beyond the inflection point and we put more and more into it and get less and less out.
