Human size in the galaxy

[Teeth]

That kind of reasoning only works if you consider extremly short distances (aka not letting the spaceship reach decent speed) in space filled with a lot of stuff that creates friction and attraction. Once you're out of a solar system, there's almost nothing to slow you down, which means building up your speed and keeping it requires very little energy.

Having no friction and low gravity does not mean that building up speed requires little energy. You still need to accelerate mass to a speed many times that of our current space travel to even get within centuries of travel time. With the square relation between velocity and energy, getting twice the velocity means needing 4 times the energy. Getting a 100 times the velocity means needing 10000 times the energy. It is not simply a matter of having a lot of fuel, because fuel is friggin heavy and every bit of extra mass requires more energy. If you actually ever wanted to deaccelerate the craft, that would require as much energy, although the craft will probably be lighter, which you need to store as dead weight for the entire acceleration. I can't be bothered to do a calculation with some estimates, but I am quite sure accelerating a ship that can sustain humans for a century to a speed with which it would take a century to travel 5 lightyears requires a tad bit too much.

Solar sails! Because i'm certain other people skimmed my previous post cos it was a wall of text explaining the principle, in essence you use photons from the sun/any star as endless acceleration to lightspeed.

Endless but very, very slow. Though I have read an article on them and there seem to be possibilities of greatly increasing the acceleration in the future, seemed very promising. They stated that travelling to Alpha Centauri may be possible with about a century travel time. Seems like the only viable way of maybe ever doing interstellar travel. A solar sail could slow down using the light of the target star, brilliant. The payload they would be able to carry can't be much though.

[Son Of Odin]

One's ecological foot mark is a popular subject these days. If everyone who is alive today, all 7 billions, lived like we do in the West and industrial countries, we'd need at least another 4 Earth-sized planets to sustain both us and the environment.

We're killing this planet slowly.

However, Earth is capable of sustaining (correct me if I got this wrong) over 120 billion humans or something like that. Not *entirely* sure about that, read that once maybe, so could be wrong. Wouldn't not make sense though, Earth is huge. Sadly the ecosystem would collapse lon before we reached even 20 billions, considering the rate at which we consume natural resources.

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Surely you meant we are killing ourselves off the planet. "The planet is fine!" :D

[Kafein]

Having no friction and low gravity does not mean that building up speed requires little energy. You still need to accelerate mass to a speed many times that of our current space travel to even get within centuries of travel time. With the square relation between velocity and energy, getting twice the velocity means needing 4 times the energy. Getting a 100 times the velocity means needing 10000 times the energy.

I don't quite understand how you can say there's a square there. Without any other force or friction, we have F = ma. We know our mass is fixed so we don't really care about it. We want to reach a fixed speed, which is equivalent to applying a certain acceleration during a certain time. If you divide your acceleration by two, you need twice the time. And all other things remaining equal, if you want to double the goal speed you can just spend double the time. Finally, the force you apply is linear with the quantity of fuel you consume. All of this of course approximate, but still. What you say is dependant on the kind of propulsion technology that is used, as in many designs, doubling the acceleration means multiplying the fuel consumption by roughly 4. But we can double the time we spend accelerating instead.

If you had a spaceship with the power of a sportscar, let's say an acceleration of 6m/s^2, you would need 49965409 seconds to reach c, which is only 578 days. Of course, the assumption of a frictionless space is not realistic, and a sportscar maintaining maximum acceleration during 578 days straight would indeed consume a hell of a lot of gaz, but still.

[Teeth]

Ek = ½mv^2 is the relation between velocity and energy I am talking about.

If put a sportscar (1000 kg, very light one) accelerating to the speed of light in this formula and convert it to gigawatt/hour I get 1.248x10^7 or 12,482,710 gigawatt/hour. To compare, world energy consumption is 2.203x10^7 or 20,279,640 gigawatt/hour. So you would need almost 2/3rds of the energy the world produces in a year to reach lightspeed and twice that if you also actually want to stop somewhere. That is a lot of rocket fuel.

[Bjord]

Ek = ½mv^2 is the relation between velocity and energy I am talking about.

If put a sportscar (1000 kg, very light one) accelerating to the speed of light in this formula and convert it to gigawatt/hour I get 1.248x10^7 or 12,482,710 gigawatt/hour. To compare, world energy consumption is 2.203x10^7 or 20,279,640 gigawatt/hour. So you would need almost 2/3rds of the energy the world produces in a year to reach lightspeed and twice that if you also actually want to stop somewhere. That is a lot of rocket fuel.

Nice Google skills.

On a more serious note and without any scientifical sources or knowledge from my side: In Even Horizon the lost ship had this quantum core device thing that would fold space/time, drastically reducing the distance required to get to the destination.

I just hope that if this was ever invented, it wouldn't backfire and cast the ship and crew into a parallel universe where everything is ruled by chaos and evil, possessing the ship and crew, causing them to pull their own eyes out and mutilating each other. That would be a shame.

[Teeth]

High school education teaches basic physics in my country and this is almost as basic as it gets.

[Kafein]

Ek = ½mv^2 is the relation between velocity and energy I am talking about.

If put a sportscar (1000 kg, very light one) accelerating to the speed of light in this formula and convert it to gigawatt/hour I get 1.248x10^7 or 12,482,710 gigawatt/hour. To compare, world energy consumption is 2.203x10^7 or 20,279,640 gigawatt/hour. So you would need almost 2/3rds of the energy the world produces in a year to reach lightspeed and twice that if you also actually want to stop somewhere. That is a lot of rocket fuel.

You are absolutely right, I simply forgot distance when I was talking in terms of forces.

[Lt_Anders]

Ek = ½mv^2 is the relation between velocity and energy I am talking about.

If put a sportscar (1000 kg, very light one) accelerating to the speed of light in this formula and convert it to gigawatt/hour I get 1.248x10^7 or 12,482,710 gigawatt/hour. To compare, world energy consumption is 2.203x10^7 or 20,279,640 gigawatt/hour. So you would need almost 2/3rds of the energy the world produces in a year to reach lightspeed and twice that if you also actually want to stop somewhere. That is a lot of rocket fuel.

Kinetic Energy formula(Had to google it since your notation is different from the stuff I learned). You do forget, that unlike in Earth, you can technically speed up indefinitely as there is almost no friction to slow you down. So without increasing your mass, you can use gravity, thrusters, and even "pushing" the ship to make it go faster. Giving yourself an acceleration a 1m/s^2 will last continuously in space so you could, with nothing more than a simple burst of energy get those speeds. Remember, An object will stay in motion unless acted on by an outside force. and in space, the amount of "outside forces" is pretty low.
But, you would be correct in the amount of energy needed. That's why I said up above that long distance travel at or near relativistic speeds just will not work with our current understanding of math principals. Once we do start moving more in space, I am quite confident we will start developing better mathematical  understanding of how to move in space.

A fuel based system just won't work. Also, launching from Earth is 100 times harder than doing almost anything in space. Our first priority should be to get into space/moon and then go from there. Once we have a way to easily get into space, the rest starts happening easier.

[Teeth]

Giving yourself an acceleration a 1m/s^2 will last continuously in space so you could, with nothing more than a simple burst of energy get those speeds

This is not true. The acceleration will not last continously, the speed you gain from the acceleration will last continously until counteracted by deacceleration. Acceleration does in fact require consistent pushing. Giving yourself an acceleration of 1m/s^2 for 1 second will make you go 1 m/s until more acceleration or deacceleration is applied, even in space. My calculation perfectly shows the amount of energy required for a 1000kg to be accelerated to lightspeed from 0 in a vacuum without any friction or gravity. I am not forgetting anything.

Remember, An object will stay in motion unless acted on by an outside force. and in space, the amount of "outside forces" is pretty low.

Yes, stay in motion indeed, not increase in speed of motion.

[Teeth]

That's why utilizing gravitational fields or solar sails is so viable in space, those would give you constant acceleration (or in the case of gravity; infrequent bursts to further increase your already high speeds), however the only issue i can forsee is that you can take as long as you like to accelerate, stopping at your destination may be difficult lol. That's where you'd need copious amounts of fuel, likely more than any ship could realistically carry. A shame, but it seems crazy physics and folding space is our only hope.

Well, with the aforementioned solar sails stopping is not much of a problem as long as you are travelling towards another star, just turn your sails away from your home star and towards the destination star, or any star close to the actual destination.

[CrazyCracka420]

SHOL'VA KREE!

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Silence, inferior beings.

Shak'ti'qua

Your manners in the presence of a God are unspeakable. Slaves is what you are. Slaves of the mighty Goa'Uld. Ya wan, ya daru.

You need not know what lies beyond the rancid hole you are to spend your whole life in, mining Naquadah, slaving for your God. The alphas of your race will serve as vessels for the Goa'Uld and consider that an honor.

*whip*

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[EponiCo]

Ek = ½mv^2 is the relation between velocity and energy I am talking about.

If put a sportscar (1000 kg, very light one) accelerating to the speed of light in this formula and convert it to gigawatt/hour I get 1.248x10^7 or 12,482,710 gigawatt/hour. To compare, world energy consumption is 2.203x10^7 or 20,279,640 gigawatt/hour. So you would need almost 2/3rds of the energy the world produces in a year to reach lightspeed and twice that if you also actually want to stop somewhere. That is a lot of rocket fuel.

Actually the energy is far higher since acceleration becomes more expensive the faster you are. The formula is something with
sqrt(n / (1- v²/c²)). Reaching speed of light would require infinite energy. Also, nitpick, but you are confusing gigawatt-hours with gigawatt/hour.

[Kafein]

Actually the energy is far higher since acceleration becomes more expensive the faster you are.

Not in a frictionless vacuum. But in space you are pretty much right I guess.

Another problem with these approximations is that classical kinematics don't work so well when when close to lightspeed.

[EponiCo]

I am talking about relativistic kinetics.
http://en.wikipedia.org/wiki/Acceleration#Relation_to_relativity

But yeah, the odd particles creating friction could be also a problem if you crash a speed of light ship into them.

[Bjord]

What about ion drive propulsion?

Also, wouldn't a constant force of energy cause the vessel to continuously accelerate faster in space? If there's no counter-active force, wouldn't said vessel accelerate infinitely?