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Mokum
07-03-2009, 05:49 PM
An unmanned Nasa mission to search the sky for Earth-like planets with the potential to host life has launched from Cape Canaveral in Florida.

The Kepler telescope will orbit the Sun to watch a patch of space thought to contain about 100,000 stars like ours.

What do you think, is there anybody out there?

http://news.bbc.co.uk/2/hi/science/nature/7918497.stm

Rincewind
07-03-2009, 08:15 PM
What do you think, is there anybody out there?

I think there is almost certain life elsewhere in the universe. In fact almost certainly I think in our galaxy. Perhaps even on other moons or planets of our solar system. Is there life producing signs of its existence close enough to us for us to detect right now? Not to date and perhaps not for some time to come.

Ian Murray
07-03-2009, 08:39 PM
...if it is just us... seems like an awful waste of space
- Ellie Alloway (Jodie Foster), movie Contact 1997

antichrist
08-03-2009, 04:01 PM
Biggest waste of money along with nuke weapons etc and in USA where of this was developed the rich companies avoid tax so is mostly paid for by the worker, and the companies get more rich because of it.

The workers are the suckers coz they are conned into crawling up to such "marvels".

Sinister
08-03-2009, 07:56 PM
it impossible for there to be no life elsewhere...Earth can't be the only planet with life but even if we made contact with "aliens" the government wouldn't tell us because we can't handle it, we are too narrow minded

Ian Murray
08-03-2009, 08:32 PM
it impossible for there to be no life elsewhere...Earth can't be the only planet with life but even if we made contact with "aliens" the government wouldn't tell us because we can't handle it, we are too narrow minded

The Fermi Paradox - theoretically the odds are that our galaxy alone should be teeming with intelligent life, all busily colonising neighbouring stars. After 10.5 billion years, why haven't they arrived here?

kjenhager
08-03-2009, 08:35 PM
After 10.5 billion years, why haven't they arrived here?
Maybe that's those "football field" sized observed flying objects ?

Ian Murray
08-03-2009, 08:50 PM
Maybe that's those "football field" sized observed flying objects ?

One of the possible paradox solutions - they have arrived but no-one believes it

Basil
08-03-2009, 08:51 PM
One of the possible paradox solutions - they have arrived but no-one believes it
Fantastic! Where's Ax!?

Ian Murray
08-03-2009, 08:53 PM
Another possible solution of course is that there are no other intelligent lifeforms

Ian Murray
08-03-2009, 08:54 PM
Or we are too insignificant to bother with

Ian Murray
08-03-2009, 08:55 PM
Or too isolated from the galactic centre (the hub of civilisation?!)

Basil
08-03-2009, 08:59 PM
Another possible solution of course is that there are no other intelligent lifeforms
Fantastic! Where's Ax!?

Ian Murray
08-03-2009, 09:26 PM
Fantastic! Where's Ax!?

I really don't think you're taking this seriously :hmm:

Basil
08-03-2009, 10:02 PM
I really don't think you're taking this seriously :hmm:
Actually I think it's very interesting, one of the more interesting on the BB. The question and possible solutions are truly fantastic - it's the banal discussion that follows to which I object (so I'm getting in first ;)).

Ian Murray
08-03-2009, 10:21 PM
Actually I think it's very interesting, one of the more interesting on the BB. The question and possible solutions are truly fantastic - it's the banal discussion that follows to which I object (so I'm getting in first ;)).

It is a fascinating subject. Putting aside all the crackpot theories, alien abductions etc, we're left with we lot called humanity sitting on a nice blue planet tucked away in a remote corner of a galaxy in a universe with more galaxies than humans. And we think we're special somehow!

Spiny Norman
09-03-2009, 06:06 AM
And we think we're special somehow!
Given that, in terms of actual evidence to hand, we are the only planet on which life exists, its a reasonable conclusion to draw. If/when other evidence is made available to the contrary, those who think we are special (myself included) can take that into account.

Rincewind
09-03-2009, 06:35 AM
Given that, in terms of actual evidence to hand, we are the only planet on which life exists, its a reasonable conclusion to draw. If/when other evidence is made available to the contrary, those who think we are special (myself included) can take that into account.

I don;t think it is reasonable at all. As we have only explored a very small proportion of planets inour own solar system and the universe comprises billions and billions of similar solar systems, why should we think that life only started on one?

Ian Murray
09-03-2009, 07:35 AM
Given that, in terms of actual evidence to hand, we are the only planet on which life exists, its a reasonable conclusion to draw. If/when other evidence is made available to the contrary, those who think we are special (myself included) can take that into account.

Absence of evidence is not evidence of absence
- Carl Sagan

Spiny Norman
09-03-2009, 07:51 AM
Absence of evidence is not evidence. In the absence of evidence, belief should be suspended, until such time as evidence is presented.

Absence of evidence, despite a theoretical large number of planets (which also is as yet unobserved), is a perfectly good reason for skepticism in this case.

The speculations of scientists who, observing spectral lines of H2O wildly extrapolate this to mean "planet capable of supporting life", shows merely how desperately they need to believe something to support their world view.

Bruce Oates
09-03-2009, 10:08 AM
Absence of evidence is not evidence. In the absence of evidence, belief should be suspended, until such time as evidence is presented.

Absence of evidence, despite a theoretical large number of planets (which also is as yet unobserved), is a perfectly good reason for skepticism in this case.

The speculations of scientists who, observing spectral lines of H2O wildly extrapolate this to mean "planet capable of supporting life", shows merely how desperately they need to believe something to support their world view.

Maybe all of those other possible life forms have bibles & don't believe
in mad scientists either.
I don't think their carrier pidgeons will ever reach us :hmm:

Ian Murray
09-03-2009, 10:22 AM
From a religious viewpoint, why assume that God only chose Earth to create, condemn and redeem intelligent life? The scenario could be replicated any number of times elsewhere.

Included could be races which did not fall from grace and so require no redemption.

Spiny Norman
09-03-2009, 10:27 AM
I'm not assuming, I'm just trying to follow the evidence. I'm happy to believe in alien life once someone shows me the evidence for it. Until then, given the probabilities associated with idea of spontaneous generation of life on this planet, I will remain skeptical about life elsewhere.

Garrett
09-03-2009, 10:59 AM
The Fermi Paradox - theoretically the odds are that our galaxy alone should be teeming with intelligent life, all busily colonising neighbouring stars. After 10.5 billion years, why haven't they arrived here?

perhaps our gravity was too strong, or too much poisonous nitrogen in our atmosphere, or not enough oxygen, perhaps chlorophyll is poisonous to them, or they have no defence to mosquitoes, or were repulsed by George W Bush.

Who knows ha ha ha.

Cheers
Garrett.

Capablanca-Fan
09-03-2009, 11:35 AM
Or too isolated from the galactic centre (the hub of civilisation?!)
Not with a black hole there! Actually, our sun is at an ideal distance from the centre (http://creation.com/the-sun-our-special-star-creation-magazine): the co-rotation radius where star velocity matches the velocity of the spiral arms, so the sun won't cross the arms and be exposed to supernovae.


Absence of evidence is not evidence of absence
- Carl Sagan
He's wrong. It is evidence, just not proof.


From a religious viewpoint, why assume that God only chose Earth to create, condemn and redeem intelligent life? The scenario could be replicated any number of times elsewhere.
Because God became incarnate on Earth, taking on only human nature, dying for humans, and rising from the dead, and now sits at the right hand of God the Father. He did not take on Vulcan or Klingon nature for instance.


Included could be races which did not fall from grace and so require no redemption.
Yet they would be affected by the curse on the whole creation due to Adam's Fall (http://creation.com/cosmic-and-universal-death-from-adam-s-fall-an-exegesis-of-romans-819-23a).

For a summary, readers may also be interested in a 2004 debate about whether God created intelligent alien life forms in Science and Theology News. I took the negative side (http://www.beliefnet.com/News/Science-Religion/2004/03/Bible-Leaves-No-Room-For-Extraterrestrial-Life.aspx); while the affirmative was supported by Guy Consolmagno (http://www.beliefnet.com/News/Science-Religion/2004/03/Humans-Are-Not-Gods-Only-Intelligent-Works.aspx), ‘a Jesuit brother and astronomer at the Vatican Observatory’ (neither of us saw each other’s article before publication). It is instructive that Consolmagno admits that even the most compelling biblical evidence he can find for ETs most likely means something completely unconnected.

Desmond
09-03-2009, 01:29 PM
What is the location of God's seat, Jono?

Basil
09-03-2009, 01:51 PM
He's wrong. It is evidence, just not proof.
In much the same way as that oft and over-quoted 'Extraordinary claims require extraordinary proof' dirge. In fact, extraordinary claims simply require proof. That's all.

Ian Murray
09-03-2009, 01:54 PM
Not with a black hole there! Actually, our sun is at an ideal distance from the centre (http://creation.com/the-sun-our-special-star-creation-magazine): the co-rotation radius where star velocity matches the velocity of the spiral arms, so the sun won't cross the arms and be exposed to supernovae.

I'm referring to the galactic CBD, not the geographical centre :)


He's wrong. It is evidence, just not proof.
Whatever. Absence of proof is not proof of absence


Because God became incarnate on Earth, taking on only human nature, dying for humans, and rising from the dead, and now sits at the right hand of God the Father. He did not take on Vulcan or Klingon nature for instance.
That's on Earth. Who's to say the process wasn't repeated on Vulcan and Klingon and elsewhere - we don't have their scriptures


Yet they would be affected by the curse on the whole creation due to Adam's Fall (http://creation.com/cosmic-and-universal-death-from-adam-s-fall-an-exegesis-of-romans-819-23a).
Genesis restricts the curse of Adam to men, women and serpents. So who got it wrong, Paul or whoever wrote Genesis?

If you're right, he wasn't kidding when he said "Vengeance is mine" Everybody and everything everywhere has to pay!


For a summary, readers may also be interested in a 2004 debate about whether God created intelligent alien life forms in Science and Theology News. I took the negative side (http://www.beliefnet.com/News/Science-Religion/2004/03/Bible-Leaves-No-Room-For-Extraterrestrial-Life.aspx); while the affirmative was supported by Guy Consolmagno (http://www.beliefnet.com/News/Science-Religion/2004/03/Humans-Are-Not-Gods-Only-Intelligent-Works.aspx), ‘a Jesuit brother and astronomer at the Vatican Observatory’ (neither of us saw each other’s article before publication). It is instructive that Consolmagno admits that even the most compelling biblical evidence he can find for ETs most likely means something completely unconnected.
The Klingon scriptures might shed new light

Desmond
09-03-2009, 02:00 PM
Anything we can glean from the IPU scriptures, Ian?

Capablanca-Fan
09-03-2009, 02:12 PM
I'm referring to the galactic CBD, not the geographical centre :)
Our sun is at the galactic CBD :)


That's on Earth. Who's to say the process wasn't repeated on Vulcan and Klingon and elsewhere - we don't have their scriptures
You wanted a religious viewpoint; I gave you a Christian religious viewpoint. The Bible is right.


Genesis restricts the curse of Adam to men, women and serpents.
The ground also.


So who got it wrong, Paul or whoever wrote Genesis?
Neither. Try reading it, as well as my article The Fall: a cosmic catastrophe (http://creation.com/the-fall-a-cosmic-catastrophe-journal-of-creation-tj).


If you're right, he wasn't kidding when he said "Vengeance is mine" Everybody and everything everywhere has to pay!
I.e. the one who takes vengeance ultimately.

Space_Dude
09-03-2009, 06:24 PM
Why can't WE be the advanced society?? I mean in movies we are always the one who gets taken over by more advanced civilization... why can't we be the one who will take over the galaxy and rule the universe!!! :twisted: :twisted: :twisted: :twisted: :twisted: :twisted: :twisted: :twisted:

Ian Murray
09-03-2009, 08:21 PM
Why can't WE be the advanced society?? I mean in movies we are always the one who gets taken over by more advanced civilization... why can't we be the one who will take over the galaxy and rule the universe!!!

'cos we're not smart enough - we've a long way to go yet before we can tackle interstellar travel

We're going to need to get off eventually, as the Earth is doomed - see www.space.com/scienceastronomy/solarsystem/death_of_earth_000224.html
That's if we avoid cosmic catastrophes beforehand (an asteroid passed between the earth and moon last week). Staying on one planet obviously increases our chances of extinction

Spiny Norman
09-03-2009, 09:57 PM
Why can't WE be the advanced society?? I mean in movies we are always the one who gets taken over by more advanced civilization... why can't we be the one who will take over the galaxy and rule the universe!!! :twisted: :twisted: :twisted: :twisted: :twisted: :twisted: :twisted: :twisted:
The problem with this is that if (the more optimistic) scientists are right and there are numerous life-bearing planets around the universe, then the odds of us being the advanced one and the others being less-advanced are astronomical. Odds are about half of the others are more advanced than us. Plenty of them ought to have solved the problems of travelling long distances across the galaxy. If that's true, then where are they? Reality is that we haven't seen them (UFO fans not withstanding) therefore odds are strongly in favour of the view that there are not numerous life-bearing planets ... and its certainly very plausible that we are alone in the universe.

Rincewind
09-03-2009, 10:24 PM
The problem with this is that if (the more optimistic) scientists are right and there are numerous life-bearing planets around the universe, then the odds of us being the advanced one and the others being less-advanced are astronomical. Odds are about half of the others are more advanced than us. Plenty of them ought to have solved the problems of travelling long distances across the galaxy. If that's true, then where are they? Reality is that we haven't seen them (UFO fans not withstanding) therefore odds are strongly in favour of the view that there are not numerous life-bearing planets ... and its certainly very plausible that we are alone in the universe.

I suspect the problems of travelling vast distances are more difficult to solve than you think. Perhaps "they" are not here because it is very difficult to make the trip and/or they have no good enough reason to come here. Even if travel across vast interstellar distances is possible it still has to consume resources and so a good reason for such a trip would be needed.

Another option (which I think is less likely) is that we are the only life bearing planet in this galaxy but that doesn't mean other galaxies are all barren of life. The problems of crossing interstellar space are small when compared to the problems of travelling intergalactic distances.

Ian Murray
09-03-2009, 10:41 PM
I suspect the problems of travelling vast distances are more difficult to solve than you think. Perhaps "they" are not here because it is very difficult to make the trip and/or they have no good enough reason to come here. Even if travel across vast interstellar distances is possible it still has to consume resources and so a good reason for such a trip would be needed.

Another option (which I think is less likely) is that we are the only life bearing planet in this galaxy but that doesn't mean other galaxies are all barren of life. The problems of crossing interstellar space are small when compared to the problems of travelling intergalactic distances.

At our current level of technological advance, the travel problems are insurmountable - it would take many generations to reach the nearest stars. However who's to know how close we can get to light speed in centuries to come - 1%, 2%, 10% ?

An analogy is the Spanish colonisation of the New World. Whether their galleons peaked out at 5 knots or 20 knots is irrelevant - they got there.

As for DeMann's interest in conquest, interstellar warfare would be appallingly resource-hungry, to the extent that it would be unthinkable. With apologies to Star Wars, any civilisation advanced enough to travel between stars would, we hope, have the nous to opt for peaceful coexistence.

Spiny Norman
10-03-2009, 05:44 AM
Perhaps they did visit and didn't like what they saw, so have quarantined us ... (n.b. I am now resorting to story-telling, a favourite pastime of those who lack any evidence and require an explanation for the illogical or unlikely).

Desmond
10-03-2009, 07:54 AM
The problem with this is that if (the more optimistic) scientists are right and there are numerous life-bearing planets around the universe, then the odds of us being the advanced one and the others being less-advanced are astronomical. Odds are about half of the others are more advanced than us. Plenty of them ought to have solved the problems of travelling long distances across the galaxy. If that's true, then where are they? Reality is that we haven't seen them (UFO fans not withstanding) therefore odds are strongly in favour of the view that there are not numerous life-bearing planets ... and its certainly very plausible that we are alone in the universe.Why so quick to dismiss the eyewitness accounts from the "UFO fans"? According to Jono the bible should be believed because it is based on eyewitness accounts.

Rincewind
10-03-2009, 07:55 AM
(n.b. I am now resorting to story-telling, a favourite pastime of those who lack any evidence and require an explanation for the illogical or unlikely).

Yep, Stone age middle-eastern tribes were also fond of that past-time.

Spiny Norman
10-03-2009, 04:28 PM
Re: the distance travel problem ... we have every reason to expect that at least some of the other proposed galactic civilisations:
(1) advanced at a much more rapid rate than humans;
(2) developed at a much earlier stage than humans; and therefore
(3) should have had millions of extra years in which to spread out across the galaxy (galaxies?) and solve their travelling distance problems

Some of them ought to have developed reasonably close to earth, and therefore should have faced far fewer distance problems.

Spiny Norman
10-03-2009, 04:29 PM
Why so quick to dismiss the eyewitness accounts from the "UFO fans"?
Lets be honest ... they're kooky! :owned:

Rincewind
10-03-2009, 04:48 PM
Re: the distance travel problem ... we have every reason to expect that at least some of the other proposed galactic civilisations:
(1) advanced at a much more rapid rate than humans;

I think more rapidly than humans would be difficult. We went from speciation to thermonuclear weapons in less than 10 million years. Which is not too shabby. Certainly not much scope for shaving off more than 1 or 2 million years here.


(2) developed at a much earlier stage than humans; and therefore

This is possible. But perhaps technology is not something many species get in to. We seem to have been the only ones to do so despite long ages where fish and dinosaurs "ruled the earth". Looking at the history of the earth there has been something like at least half a billion years of life covering the globe and only around a million years of technology. This at least suggests that life can positively thrive without technology and perhaps technology is a difficult business to get into.


(3) should have had millions of extra years in which to spread out across the galaxy (galaxies?) and solve their travelling distance problems

Again perhaps that is true provided they developed technology and it solved the distance travel problem. However the distance problems cannot be made to evaporate by some hand waving. Most of the stars in our galaxy are more than 26,000 light years away.


Some of them ought to have developed reasonably close to earth, and therefore should have faced far fewer distance problems.

Reasonably close as is 26,000 light years? (That is less than half of the stars in our galaxy). Even the next-door neighbours a measly 1,000 light years away still face huge problems travelling distances which take light 1,000 years to traverse.

Perhaps faster than light travel will be cracked but it does seem to present fundamental problems with the space time continuum. If you believe in relativity which has been shown to be pretty good as an abstraction of reality.

Ian Murray
10-03-2009, 06:58 PM
...But perhaps technology is not something many species get in to. We seem to have been the only ones to do so despite long ages where fish and dinosaurs "ruled the earth". Looking at the history of the earth there has been something like at least half a billion years of life covering the globe and only around a million years of technology. This at least suggests that life can positively thrive without technology and perhaps technology is a difficult business to get into....
As well as intelligence, developing technology also requires toolmaking ability. We would not be on top (for the moment) of the Terran evolutionary tree without our habile upper limbs and opposable thumbs.

ET would need to have evolved along somewhat similar lines to get into the space race. Just how similar and how different invites endless speculation


Perhaps faster than light travel will be cracked but it does seem to present fundamental problems with the space time continuum.

Which really is a shame. The hyperdrive and warp speed would make it all so much easier :)

morebeer
11-03-2009, 07:23 AM
Lets be honest ... they're kooky! :owned:

They are not the only ones!

antichrist
11-03-2009, 04:51 PM
Because God became incarnate on Earth, taking on only human nature, dying for humans, and rising from the dead, and now sits at the right hand of God the Father. He did not take on Vulcan or Klingon nature for instance.




what is special about the right hand of God, what is in the left or who sits there? The nuns used to tie the left hand of lefties behind their back when I was young so that they could not write with the devil's hand. Is God's hand also tied behind his back and is no one allowed to sit there? Does he fart out that side?

Capablanca-Fan
11-03-2009, 05:49 PM
what is special about the right hand of God, what is in the left or who sits there? The nuns used to tie the left hand of lefties behind their back when I was young so that they could not write with the devil's hand. Is God's hand also tied behind his back and is no one allowed to sit there? Does he fart out that side?
Stop whinging. There is nothing in the Bible against left-handedness; some left-handers were noted for their battle prowess for the good guys. But in ancient kingdoms of the middle east, a king's sitting someone at his right hand was declaring that person an equal.

Kevin Bonham
11-03-2009, 08:46 PM
Absence of evidence is not evidence. In the absence of evidence, belief should be suspended, until such time as evidence is presented.

Then why did you say that the conclusion that we are special is a reasonable one to draw? There's no remotely convincing evidence for that either.


The speculations of scientists who, observing spectral lines of H2O wildly extrapolate this to mean "planet capable of supporting life", shows merely how desperately they need to believe something to support their world view.

Same thing could be said about religious commentators who are sceptical of the likelihood of life elsewhere.


The problem with this is that if (the more optimistic) scientists are right and there are numerous life-bearing planets around the universe, then the odds of us being the advanced one and the others being less-advanced are astronomical.

But if the more pessimistic scientists/non-scientists are right and there is only one life-bearing planet around the universe, then the odds against this being the one with life would also be astronomical (if we didn't already know there was life here). So I don't see what this argument acheives and it looks like a similar instance of lottery-winner fallacy to those often found in improbability of congenial conditions type arguments for God.


Odds are about half of the others are more advanced than us.

Another fallacy (principle of indifference). We could be anywhere on the spectrum and it would actually be surprising if we were especially close to the middle rather than some distance from it in one direction or other.

From a scientific viewpoint we just don't know whether there is life elsewhere and we are not close to knowing either way. My own speculative view on this is that the existence of life elsewhere is a virtual certainty and intelligent life elsewhere very likely. But it may well be that intelligent and technologically capable life is sparse and I certainly don't expect evidence of it to be found any century soon.

As for very simple life I would not be greatly surprised if that was discovered on other bodies in our solar system. Arguments of the form "environments of type X are needed for life, X only exists on earth, hence there is no other life in the solar system" have been running for cover in recent decades as life forms have been found on earth in environments not of type X. Also there is a tendency for our knowledge of potentially life-supporting environment types in the solar system to expand over time (for a while it's thought there's no X on Mars, then it turns out there might be, etc)

Ian Murray
11-03-2009, 08:53 PM
Perhaps faster than light travel will be cracked but it does seem to present fundamental problems with the space time continuum. If you believe in relativity which has been shown to be pretty good as an abstraction of reality.

For those who came in late, the fundamental problems arise from Einstein's special theory of relativity, which applies to objects travelling at speeds approaching lightspeed -

An object accelerating to reach the speed of light gains infinite kinetic energy, i.e. would require infinite power to reach lightspeed or fixed power over an infinite period of time. It follows that no physical object can reach lightspeed.

At velocities close to lightspeed, objects progressively gain momentum and length, while time slows.

So endeth my layman's lesson. I'm confident Rincewind can correct the errors athematically.

Desmond
12-03-2009, 08:41 AM
Stop whinging. There is nothing in the Bible against left-handedness; some left-handers were noted for their battle prowess for the good guys. But in ancient kingdoms of the middle east, a king's sitting someone at his right hand was declaring that person an equal.But where are they sitting? I mean Jesus's corporeal form is meant to have risen up of the ground and floated away to somewhere. Did it leave orbit? Sitting on a cloud somewhere?

ER
12-03-2009, 07:20 PM
... Did it leave orbit? ...
Nop and that maybe was a divine message against careless fuel consumption! :owned:
Although I agree that the lack of it might have caused the event being less spectacular! :P

Rincewind
12-03-2009, 11:10 PM
At velocities close to lightspeed, objects progressively gain momentum and length, while time slows.

I'm a layman too when it comes to relativity but by understanding that lengths decrease in the direction of travel. So if anything they lose length, a phenomenon known as Lorentz contraction.

To return to more familiar territory for me... Lorentz also gave his name to a well known delta convergent sequence, the Lorentzian...

epsilon / pi(epsilon^2 + x^2)

which converges to delta(x) in the limit of epsilon approaching 0+. Some will also know it as a Cauchy distribution.

Capablanca-Fan
13-03-2009, 08:36 AM
For those who came in late, the fundamental problems arise from Einstein's special theory of relativity, which applies to objects travelling at speeds approaching lightspeed —

An object accelerating to reach the speed of light gains infinite kinetic energy, i.e. would require infinite power to reach lightspeed or fixed power over an infinite period of time. It follows that no physical object can reach lightspeed.

At velocities close to lightspeed, objects progressively gain momentum and length, while time slows.
As RW said, there is a length contraction, but right on the other counts. The amount is the Lorenz factor (γ), which is related to the fraction of the speed of light β (v / c): γ = 1/√(1-β²). It's not that much at half the speed of light (1.155), but at 90% of c it's over twice, 99% over 7 times, 99.9% over 20 times.

But a major problem for interstellar travel occurs well before relativistic effects are significant:

For a spacecraft to acquire the tenth of the speed of light, which would mean 40 years to reach the nearest star outside our solar system, it would need to acquire kinetic energy. This given accurately enough by the non-relativistic formula of ½mv². For a very small unmanned spacecraft of 10 kg, this is:

½ x 10 kg x (3 x 10^7 m/s)²
= 4.5 x 10^15 J

The largest hydro-electric power station in the world at present, Itaipu, is jointly run by Brazil and Paraguay and has an output of 12.6 million kilowatts. Total energy generated by the 18 turbines in four days is exactly equal to the kinetic energy of the above-mentioned 10 kg spacecraft moving with a speed of c/10.

For a manned spacecraft weighing several tonnes, the energy requirements would exceed the world’s annual electricity consumption. For the city-sized spacecrafts in Independence Day, the energy requirements would be even more staggering. And when the spacecraft slowed again, it would need to use up almost this amount of energy in braking. If the spacecraft had to accelerate to c/10, slow down and start up many times, it is hard to imagine how enough fuel could be carried.

It would probably be impossible without some sort of antimatter drive. If perfect annihilation—complete conversion of matter to energy (E = mc²)—were possible, 1 tonne of antimatter could annihilate 1 tonne of ordinary matter to produce:

2000 kg x (3 x 10^8 m/s)²
= 1.8 x 10^20 J.

And this is the absolute maximum amount of energy which could be produced even in principle from a given mass of fuel. A real spacecraft would be nowhere near as efficient.

Another problem is the collision with particles in space. The kinetic energy of a particle with a mass of a tenth of a gram travelling at a tenth of the speed of light, calculated from the spacecraft’s reference frame, is:

½mv²
= ½ x 10^–4 kg x (3 x 10^7 m/s)²
= 4.5 x 10^10 J.

In a chemistry lexicon (Roempp Lexikon), the combustion energy of TNT is given as:

4,520 kJ/kg
= 4.52 x 10^9 J/tonne

Therefore 4.5 x 10^10 J is equivalent to:
(4.5 x 10^10)/(4.52 x 10^9)
= 9.95 tons of TNT.
Therefore the impact energy of one of those 0.1 g objects would be the equivalent of an explosion of about 10 tons of TNT.

Garrett
13-03-2009, 11:22 AM
yes - A great answer to the 'well why aren't they here?' question.

The cost for interstellar exploration would be astronomical, so why send a spacecraft off the examine a planet orbiting a G type star when it is off on a 'spur' of the galactic arm. Would make much more sense to send probes off to more populated areas in the habitable zone.

cheers
Garrett.

Ian Murray
14-03-2009, 11:54 PM
...But a major problem for interstellar travel occurs well before relativistic effects are significant:

For a spacecraft to acquire the tenth of the speed of light, which would mean 40 years to reach the nearest star outside our solar system, it would need to acquire kinetic energy. This given accurately enough by the non-relativistic formula of ½mv². For a very small unmanned spacecraft of 10 kg, this is:

½ x 10 kg x (3 x 10^7 m/s)²
= 4.5 x 10^15 J

For a manned spacecraft weighing several tonnes, the energy requirements would exceed the world’s annual electricity consumption. For the city-sized spacecrafts in Independence Day, the energy requirements would be even more staggering. And when the spacecraft slowed again, it would need to use up almost this amount of energy in braking. If the spacecraft had to accelerate to c/10, slow down and start up many times, it is hard to imagine how enough fuel could be carried.

It would probably be impossible without some sort of antimatter drive. If perfect annihilation—complete conversion of matter to energy (E = mc²)—were possible, 1 tonne of antimatter could annihilate 1 tonne of ordinary matter to produce:

2000 kg x (3 x 10^8 m/s)²
= 1.8 x 10^20 J.

And this is the absolute maximum amount of energy which could be produced even in principle from a given mass of fuel. A real spacecraft would be nowhere near as efficient.

What once were pipe dreams are now on the drawing board and under test. A spacecraft powered by the Mini-Mag Orion propulsion system could reach a speed of c/10 (http://thefutureofthings.com/news/1006/mini-mag-orion-will-reach-for-the-stars.html), while anti-matter systems as an alternative to nuclear-powered craft are under laboratory examination (http://thefutureofthings.com/articles/33/new-antimatter-engine-design.html) And the photon laser has been bench-tested - www.associatedcontent.com/article/394385/photon_propulsion_system_could_revolutionize.html? cat=15


Another problem is the collision with particles in space. The kinetic energy of a particle with a mass of a tenth of a gram travelling at a tenth of the speed of light, calculated from the spacecraft’s reference frame, is:....
Therefore the impact energy of one of those 0.1 g objects would be the equivalent of an explosion of about 10 tons of TNT.

Strikes by cosmic dust particles travelling at such speeds were a concern when planning the manned lunar missions, but the threat proved to be negligible. Of greater concern is the risk to manned missions of increased radiation during solar flares.

Rincewind
15-03-2009, 12:24 AM
such speeds were a concern when planning the manned lunar missions, but the threat proved to be negligible. Of greater concern is the risk to manned missions of increased radiation during solar flares.

Was that due to the particles not being as destructive as planned or just due to their absence?

In Jono's working he is assuming the particles are stationary and just appear to be moving at c/10 because we are talking about things relative to the spaceship's frame of reference.

In comparison with the manned lunar missions the spaceship only got up to around c/30000 (around 10 km / s or so) which is substantially smaller than the speeds Jono was working with.

Ian Murray
15-03-2009, 11:30 PM
Was that due to the particles not being as destructive as planned or just due to their absence?

In Jono's working he is assuming the particles are stationary and just appear to be moving at c/10 because we are talking about things relative to the spaceship's frame of reference.

In comparison with the manned lunar missions the spaceship only got up to around c/30000 (around 10 km / s or so) which is substantially smaller than the speeds Jono was working with.
As far as I can ascertain (biblio below) the near-earth dust density is 2x10-21g/cm3 at velocities of up to 12 km/sec, depending on how deep into earth's gravity well. The risk of impact with a spacecraft is low and acceptable, with manageable puncture or abrasion damage.

Outside the solar system the density of interstellar matter is far lower than in the best laboratory vacuum, the total mass contained between stars is about 5% of the mass of the universe. Interstellar matter is mostly gaseous, but about 1% is interstellar grains or dust. The grains are not distributed uniformly in space but are found in clumpy clouds.

The impact risk is thus low, but still undesirable at c/10! Presumably the astronavigation calculations would include avoiding dust clouds. In the event of impact with a stray micrometeor, would the particle simply punch straight through the craft, leaving entry and exit holes a few microns wide (cf bullet holes)? I can't find an answer to that.

http://articles.adsabs.harvard.edu/cgi-bin/nph-iarticle_query?1964IrAJ....6..260O&defaultprint=YES&filetype=.pdf
http://www.answers.com/topic/interstellar-medium-2

Capablanca-Fan
16-03-2009, 12:37 AM
What once were pipe dreams are now on the drawing board and under test.
Sure, but they can't escape the fundamental laws of physics like E=½mv². This is enough of a problem even before relativistic effects add to it.


A spacecraft powered by the Mini-Mag Orion propulsion system could reach a speed of c/10 (http://thefutureofthings.com/news/10...he-stars.html), while anti-matter systems as an alternative to nuclear-powered craft are under laboratory examination (http://thefutureofthings.com/article...ne-design.html)
My calculations of the energy required still stand. Note that we have only made particle amounts of antimatter so far, far from the tons required.


As far as I can ascertain (biblio below) the near-earth dust density is 2x10-21g/cm3 at velocities of up to 12 km/sec, depending on how deep into earth's gravity well. The risk of impact with a spacecraft is low and acceptable, with manageable puncture or abrasion damage.
But there are a lot of cm³ in the 4 ly path of a craft to the nearest star.


The impact risk is thus low, but still undesirable at c/10! Presumably the astronavigation calculations would include avoiding dust clouds. In the event of impact with a stray micrometeor, would the particle simply punch straight through the craft, leaving entry and exit holes a few microns wide (cf bullet holes)? I can't find an answer to that.
At that speed, enormous amounts of energy would be dissipated in the structure. They would do considerable damage if they hit a human. Even subatomic particles passing through matter cause ionization and lattice defects.