Traveling to Alfa Centauri at 1/2 the speed of light

[3rdHeaven]

I was going by memory, you see how well that goes.

I realize the Carter Doomsday Argument is not absolute, but can be used as a estimator. No one knows how long we really have, one thing is certain, we don't have a whole lot of time because even if humans can survive another 2 million years, life on Earth will be a lot hotter as our sun approaches a red giant and collapse. Evolution might even appear to reverse as this happens before all the water evaporates.

The point I was trying to make and I should have taken the time to be more accurate instead of going by memory, is man has been around for 200,000 years. You would think by now we would have that advanced technology, but are no where near it. I'm sure given the opportunity to continue we will advance more, but if we really went by our past, it might not be that significant. An earlier poster used the technology advances we made in the past 200 years as an example of perhaps some major break through to happen in the next 200 years. I don't see that. Not the break through we would need for interstellar travel. I think we would need at least 10,000 more years. If we make it. That was my point I was trying to make. Thank you for taking me seriously enough to indulge me further! I'm glad I found this forum looks like a goldmine of information.

 

[Ryan_m_b]

I was going by memory, you see how well that goes.

I realize the Carter Doomsday Argument is not absolute, but can be used as a estimator. No one knows how long we really have, one thing is certain, we don't have a whole lot of time because even if humans can survive another 2 million years, life on Earth will be a lot hotter as our sun approaches to turn into a giant red giant and collapse. Evolution might even appear to reverse as this happens before all the water evaporates.

Evolution never reverses though it can lead to convergent evolution wherein a species evolves a similar phenotype to an existing or former species to address the same issue (e.g. the shape of dolphins and sharks). Also I don't think in 2 million years the environment will be that much different, the progression of the Sun to a red giant will take billions of years so we'd be looking at time scales of hundreds of millions - billions for any significant effect.

The point I was trying to make and I should have taken the time to be more accurate instead of going by memory, is man has been around for 200,000 years. You would think by now we would have that advanced technology, but are no where near it. I'm sure given the opportunity to continue we will advance more, but if we really went by our past, it might not be that significant. An earlier poster used the technology advances we made in the past 200 years as an example of perhaps some major break through to happen in the next 200 years. I don't see that. Not the break through we would need for interstellar travel. I think we would need at least 10,000 more years. If we make it. That was my point I was trying to make. Thank you for taking me seriously enough to indulge me further! I'm glad I found this forum looks like a goldmine of information.

I don't think you can really put a time on these things but the idea that perhaps we could have progressed differently is an interesting one e.g. could we have adopted settled rather than hunter gatherer lifestyle kiloyears sooner? Wrt interstellar travel I really don't think it's that pressing a concern for our continued existence. To borrow from Tom Murphy (UCLA professor)

When driving, fixing your gaze on the gleaming horizon is likely to result in your crashing into a stopped car ahead of you, so that your car is no longer capable of reaching the promised land ahead. We have to pay attention to the stupid stuff right in front of us, as it might well stand between us and a smart future.

If survival of the human race is your goal there are far more important things to focus on in the short-medium term for which the impracticality of mass space colonisation is not an answer.

Hope you enjoy the forum! It certainly is a great place to learn about science.

 

[TheTechNoir]

Ryan makes good points. Also, while they can be considered modern humans in a sense, if a mother gave birth to a human identical to humans as they were then, but right now... He wouldn't be able to make it out of elementary school most likely. On that time scale we only just recently left Africa. If you look at progression, with the exception of the counter-productive dark ages it's actually been pretty good and as more and more of a foundation/base is built we've become far more technologically advanced far more rapidly. From not knowing what fire is to having a now 100 year old theory of quantum mechanics is a pretty gigantic leap forward considering when you don't know what fire is yet, how much longer it would take then right now to make any type of advancement.

I wish I could look at a crystal ball and see how this goes but it's definitely pure speculation.

Cheers

 

[3rdHeaven]

It is speculation, but isn't it grand just the same?!

I think Quantum Physics will continue to play a major role in advances.

I was addressing interstellar travel because it seems that's what this thread is about. While not a burning desire or interest of mine, I do find it interesting nevertheless.

Have any of you ever visited any paranormal forums, now that's were things get really insane. When it gets to alien visitations and ufo's. I usually can not resist and get involved in such discussion by being perfectly honest with them. I remind them first of the level of technology they would have had to master just to get here from the nearest galaxy. So *IF* they finally get that far and visit us, why is it all their space ships look like cheap cigars and saucers with "flashing lights"? That hopefully will get them thinking. I would love to become a believer, but have not seen any credible evidence yet.

 

[qraal]

A Shuttle Orbiter masses ~85 tons. To propel it to 0.5c and then decelerate back to the local standard of rest requires a mass-ratio of 3 if we could operate it as a perfect photon rocket. Thus total energy required is ~1.7E+5 kg x 9E+16 J = 1.53E+22 J. About 87,700 seconds of total sunlight striking the Earth.

Humans use 17 TW.years of energy each year. That's 5.4E+20 J. So we need ~28.5 years of total energy supply to send an Orbiter at 0.5c. About 174,000 tons of uranium or thorium totally fissioned. Sounds like a lot of energy doesn't it? The Chixulub impactor massed about 1 trillion tons and impacted at ~25 km/s. That's about 20 times the energy in the 0.5c Space Shuttle.

But energy isn't a useful measure. Power is. How much power does it take to reach 0.5c? At 1 gee the cruise speed is reached in about 15 million seconds. Average power during the boost phase is 647 TW, about 38 times the world's current energy use rate. During the braking phase it's 373 TW, about 22 times the world's energy useage rate. Sounds immense, but compared to the 122,200 TW absorbed by the Earth of the incident sunlight it's not so daunting. If we ever reach Kardashev I energy control levels, then interstellar missions might not seem so incredible. Going beyond that to K-II level and multiple interstellar missions become perfectly feasible - the Sun emits the equivalent of 4.3 million tons of energy per second. If it could be collimated into beams, then that's the equivalent of launching 258 quadrillion tons of mass to the stars at 1 gee via laser beam. The entire planet's biosphere could be launched with that kind of power supply.

 

[Vorde]

The key to interstellar travel, in my opinion, isn't a energy (or power) cost but a time cost. Barring some unforeseen massive breakthrough of clean energy that is wholly unexpected, it will be a long, long time (potentially millennia) before the human race can affordably accelerate interstellar craft to sizable fractions of c.

Instead, we should embrace the much more real possibility of slow moving (with regards to c) spacecraft that travel for long periods of time.

In this case, issues like suspended animation and generation ships begin to be considered. Ideas which are far, far cheaper on an energy scale.