I'm trying to win an argument that it is impossible to be visited by aliens. During my argument, I changed that to routinely visited by aliens. As this is totally nonsense, how do I win the argument when my opponent constantly says, "you don't know what aliens are made out of or what they are like. Maybe they are made out of something we've never seen on Earth!".

So, I say... Lets take the closest star,Centauri, and aliens started the journey towards earth. Brought their own oxygen to burn fuel or had some sort of nuclear alien fusion to get here without oxygen. Even if their bodies were made out of stainless steel, they would burn up traveling at the speed of light. So, unless they were made of something tougher than the hardest metal on earth, and still amazingly breathed thru metal lungs, they could never make it at 186,000 mi/sec for 4.3 years.

I break it down more, that humans can withstand G forces at around 2100 mph and so. By the time a breathing alien reasonably flesh-like got to earth, we would be visited by his 3rd generation b/c it couldn't withstand the G-forces necessary to get here. Unable to crunch the numbers...

How do you explain to such earthlings that it's mathmatically impossible or what logic would you use?

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I'm not sure you'll be able to win that argument, because I don't think it is impossible if you are allowed to use an arbitrary unknown energy source. To travel between stars in a few decades does not require any significant acceleration, if you can sustain it the whole time. The formula there, for approximately unrelativistic speeds, is that the acceleration needed to go a certain distance in a certain time is of order the distance divided by the square of the desired time (you can see that just from the units of acceleration.) If the distance is 10 LY, let's say, that's about 10 to the 17 m. If you wanted to get there in 30 years, let's say, that is about 10 to the 9 seconds. The required acceleration is then of order 0.1 m/s^2, which is only 1% of what we would call 1 "g". The hard part would be to maintain that acceleration for decades. Or, you could increase the acceleration and shorten the trip, though to get it less than a few years (in the traveler's reference frame) requires relativistic speeds and that requires a lot of energy. The aliens would need to very efficiently convert a significant fraction of the mass of their ship into energy, and we currently know of no way to do this. Is it theoretically impossible? I don't think so. But it can't be easy, or our solar system would be lousy with alien visitors.

In other words, I think the argument proceeds in the opposite direction that you are pushing: It's not that we know aliens aren't here because it's so difficult, we know (or suspect) it's so difficult because aliens aren't here. Of course, if someone thinks aliens are here, that argument won't convince, but then, probably they are not very conducive to listening to reason anyway!

The tree of alien life!

Paleontologist Peter Ward wants to trash the tree of life — at least the time-honored tree that we all learned about in biology class.

In his latest book, “Life as We Do Not Know It,” Ward notes that scientists are already fiddling with genetic code to create what you could arguably call alien organisms, and he proposes a grander tree — or a forest of trees — for those aliens as well as viruses, non-DNA life and silicon-carbon extraterrestrials.

"This sets the house up for admitting all these aliens," said Ward, a University of Washington professor who delves into issues surrounding ancient life as well as future life.



From the Cosmic Log, aliens are already on Earth. We just need to add viruses, the RNA world, synthetic organisms, and life elsewhere to the tree of life.

"Exobiology". I suppose it could be debated as to whether or not there really is such a field at present, but I think they are starting to crank out PhD theses and the like, so it seems to be crossing from sci fi to sci even now.

You have to accelerate then be able to slow down at the end of the journey. So if you assume a magic thruster that runs as long as it is supplied with power, you have to accelerate halfway, then turn around and use the rest of the trip to decelerate or you'll pass by your target.

Anyway, there's no physical impossibility in the statement, "We're being visited by aliens." It's just highly unlikely that they'd go unnoticed with all the telescopes and astronomers (amateur and professional) looking up all the time. Then don't forget SETI and radio telescopes. Then don't forget North American Strategic Air Command.

Of course, "radar invisibility" is always a comeback for that. It's hard to beat someone in an argument when imagination is all you need to defeat logic.

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Aliens visited me. They took me for a ride on their spaceship. It was fun. Then we went into the Bermuda Triangle, and I got to drink wine with Elvis.

o/` Cthulhu and Godzilla were doing the Hula Hula o/` - Tom Smith's "Bermuda Triangle".

I think it's interesting, the idea of exobiology and such. I would say that we wouldn't have much a use for it unless there were extraterrestrials, but I suppose if we make our own "aliens", then that's a different issue...

I wonder if we could create life that could live in Venus or Mars. That would be interesting.

It would be very tough to win an arguement that aliens (if they exist) can't visit us, when it's impossible to articulate what type of form they may have, what sort of substances they are made of, what requirements they may have for existing, (they may have different nutritional needs then us. They may not breath oxygen as we do. They may not breath at all.) What kind of technology they have available.

For example, what if a thousand of them can condense themselves to fit into a space of one cubic meter? but their ship is ten times the size of the International Space Station, and they have an antimatter annialition propulsion technology?

The G forces is a minor problem, even for us at our level of knowledge.
G forces only occur during acceleration. Once the desired speed is achieved, they can coast for years, or even decades without slowing down significantly.

The arguement that aliens can't come here is a loser. But now if you were to argue the point that aliens haven't come here, then there is no way you can lose. Because the opponent has to prove absolutley that aliens have been here, and/or are here now. Which is quite impossible short of having a newsclip of their ship landing on the front lawn of the White House, and shaking hands, paws, tenticles or whatever with the President.

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Thanks for turning down the volume. Now I can hear the voices in my head again.

You can not win your argument with the notion that light speed travel is imposable for bio genic beings. ( is that what you said, ? ) That may well be so. But that is not resson enough to prohibat alien visatation. As has been shown. A craft useing excelaration force of 1g, could quiet easly do the excelarate to halfway, and deselarate into orbit. all in about 12 years. The fact that we only live into our 80's is not an issue for a alien life form that lives for 3 hundred or so.... All I am trying to tell you is to be open to difering ideas. Just becouse you and I can not yet do some thing that does not make it imposable. Just Highly unlikly,.
To diswade the avid alien nut, I try to explain the size of the Universe and the time line since man has roamed the Earth for not yet one million years. This Solar system of ours is just four and a half bilion years in a galaxy that would seem to be about therteen point eight billion years old. The chance of us being alone in the universe is nill. But the time and distance between life forms might well prohibat us ever making contact.

Ah Ha, I didn't know this. You and Astromark nailed my question. Yes I was basing my whole argument on G-forces alone. So we accelerate only to the point when we can lift off the throttle. Puke from motion sickness, then relax.

So, I'm wrong. GEEEZ! I hate being wrong when arguing with Imaginarians.

How many mph does it take to obtain 1G? How much time and speed would it take earthlings at our present technology to visit a planet orbiting Centauri?

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Other species would of the same possibilities that we have.
And there is nothing in the laws of physics that keeps us
from travelling to other stars. It's the engineering that's a real pain.

The best we could do with foreseeable technology would be
a few percent of light-speed and then coast for the rest of the way.
It would take decades, and that's just one way.
We'll probably send robots one day though.

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Gravity is change in velocity, not velocity itself. You can express it in Miles Per Hour Per Second. IIRC, 1G is equal to approximately 20 mph/sec. Meaning, every second you add 20 mph to your velocity. Deceleration is the same as acceleration to a physicist, you are merely accelerating in a different direction. The same is true for any change in direction, even making a turn. It's all acceleration because the same math applies.

The fastest way to get from point A to point B in space is to use a thruster you can operate constantly and accelerate towards your target for halfway, then accelerate in the opposite direction for the rest of the trip.

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Actually to get to 0.1 c you only need to accelerate at one gee for around six months; it might be a little less - I can't find the exact figures at the moment.
If you can build a motor which can accelerate at 1 gee for an hour you would be doing quite well; accelerating for six months solid would be a remarkable acheivement. Imagine how much fuel and propellant that would require.

One way that such prolonged feats of acceleration might be to remove the fuel from the spacecraft, and propel it by beamed energy of some sort; high powered lasers, or even better, tiny particles of mass (a particle beam) would work to transfer momentum to a suitably lightweight vessel.

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One g for one year gets you near to light speed, so a reasonable time for a journey with hypothetical drive which would provide this acceleration is light travel time plus the best part of two years, eg six years from Alpha Centauri.

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For one thing, an alien´s "g" would be necessarilly different than other´s. If they were fragile critters from low gravity worlds, they would take longer to reach any given speed, for they could only withstand their own little g. In other words 1) take care when putting two alien species in the same spaceship; 2) Don´t mess with a high-gravity civilization: they can get here faster than you can get there.

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Don't forget relativity. Well before you get to lightspeed, you'll need to increase your thrust in order maintain 1 G of acceleration. The force you need to go faster will increase exponentially as you pass 77% of lightspeed.

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But you wouldn't notice that, because time runs faster?

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No, not in general.

If you were carrying all your propellant, you would need to
reduce your thrust as the mass of propellant decreased.

If your propellant magically appeared in your fuel tank just
at the moment you needed it, moving at the same speed as your
ship, you would not need to change your thrust at all to
maintain constant acceleration forever.

If you were propelled by light pressure from a laser beam
back in the solar system you are leaving, the power of the
laser beam would need to increase as your speed increased,
in order to maintain constant acceleration-- even if the
beam didn't spread out beyond the edges of your lightsail
at great distances.

Relativistic effects don't affect how you perceive yourself,
only how you perceive others, and how others perceive you.
It doesn't matter how fast you are moving relative to someone
else, you can always accelerate at 1 g with the same thrust,
in any direction. But if you are moving at nearly c relative
to me, I will perceive that your 1 g forward acceleration
doesn't increase your speed relative to me by much. To you,
the trip will be made shorter because the Universe appears
to shrink significantly in the direction you are traveling.

-- Jeff, in Minneapolis

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"I find astronomy very interesting, but I wouldn't if I thought we
were just going to sit here and look." -- "Van Rijn"

"The other planets? Well, they just happen to be there, but the
point of rockets is to explore them!" -- Kai Yeves

I think you're wrong about this. You're thinking of relative time. The amount of energy needed to move an object increases as velocity does. It's the very reason why lightspeed is unattainable by anything with mass. While weight reduction from fuel use will be linear, the increase in required energy for acceleration with be exponential. When you reach the threshold of lightspeed, to actually go any faster would require infinite energy, so lightspeed is unattainable through any means known to science.

This has been tested.

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I think Jeff and Faultline are both right, it's a question of reference frame. If you could maintain a 1G acceleration in your own frame, it wouldn't require any changes to the engineering of your ship, you'd just have to do it without running out of fuel (a major challenge!). From the perspective of the people back on Earth, you would not be accelerating this fast once you became relativistic, they would see all your increase of momentum going into increased relativistic mass rather than velocity.

The frame of the rocket is weird, because it is an accelerating reference frame. A 1 g acceleration would mean that objects moving with you would fall back by 9.8 m/s for every second that you accelerate. Bute note, if you notice alpha Centauri approaching you at c minus 9.8 m/s at some point in this process, if you would not see it approaching at c a second later. The 9.8 m/s would only apply to objects at rest with respect to you, the velocity addition formula would still have alpha Cen approaching at just a little faster than c minus 9.8 m/s. So it would be hard to accelerate the approach of alpha Cen as you become relativistic. No matter, what you would instead see is a shortening of the distance to alpha Cen, not quite the same thing as alpha Cen moving toward you! Back on Earth, people would not see alpha Cen approaching you at faster than the speed of light, but they would see time slowing down for you. At the end of the day, you could go very far in a short amount of time if you could really maintain 1 g. The energy challenges are another matter, I'll have to think about that, but it's clear that you'd have to convert most of the rest mass of your ship into energy to make it work.

I think I got it right, but apparently we are talking about
different things, so we may both be right:

I was referring to all relativistic effects, not just the time
dilation effect. They come as a package. You have to take all
of them if you take any.

The amount of energy needed to accelerate a mass relative to
an observer not participating in the acceleration increases
with relative speed, yes.

If you want to maintain a constant acceleration of 1 g, so
that the force you feel aboard your spacecraft is a constant
1 g, then you must decrease the thrust as your fuel is used
up, or maintain constant thrust if the fuel magically appears
in your fuel tank at the moment it is needed.

That's what I said:
When you maintain a constant acceleration of 1 g, your speed
relative to me asymptotically approaches c. But to you, the
effect is to seemingly increase your speed without limit,
because the Universe appears to become shorter and shorter in
the direction you are moving.

If you were to try to maintain a constant 1 g acceleration
relative to me, your thrust would have to increase as you say,
but you would experience exponentially-increasing acceleration,
until you are crushed, your spacecraft crumples, and you use up
all the fuel in the Universe, and you still didn't reach c
relative to me.

-- Jeff, in Minneapolis

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"I find astronomy very interesting, but I wouldn't if I thought we
were just going to sit here and look." -- "Van Rijn"

"The other planets? Well, they just happen to be there, but the
point of rockets is to explore them!" -- Kai Yeves

That's a monumental understatement.

Just to put real spacecraft such as the Space Shuttle into orbit
requires that more than 80% of the gross liftoff weight is fuel.

-- Jeff, in Minneapolis

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http://www.FreeMars.org/jeff/

"I find astronomy very interesting, but I wouldn't if I thought we
were just going to sit here and look." -- "Van Rijn"

"The other planets? Well, they just happen to be there, but the
point of rockets is to explore them!" -- Kai Yeves

what would happen if a alien species could take the energy that is transferred to the mass of the ship when approaching the speed of light, as i understand it, and transfers this energy to the engines or the propulsion of the ship, which of course uses this energy and therefore the mass of the ship does not actually increase but stays the same. all they would have to do is have the ability to keep up with the transfer of the energy from the speed of light to the propulsion system.

therefore an alien has learned how to transfer the energy at the speed of light from increasing its ships mass and transfer this enrgy to the propulsion system. therefore keeping the mass of the ship constant. the implications!!......

just thinking!!

That is a perpetual motion notion.

Energy is measured relative to something. The kinetic energy
of the ship increases relative to an outside observer because
the chemical energy in the fuel is converted to motion of the
ship and the exhaust. The resulting kinetic energy relative
to the observer is the energy of the motion. Extracting that
energy would slow the ship relative to the observer.

-- Jeff, in Minneapolis

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http://www.FreeMars.org/jeff/

"I find astronomy very interesting, but I wouldn't if I thought we
were just going to sit here and look." -- "Van Rijn"

"The other planets? Well, they just happen to be there, but the
point of rockets is to explore them!" -- Kai Yeves

but what if instead of chemical energy you used electromagnetic energy as your propulsion? the increase in mass means also that there is an increase in electromagnetic energy. therefore you conduct or direct the electromagnetic energy gained to your propulsion system is based on a N(north pole) to N repulsion system. not only that if could adjust the distance too each pole you would increase the repulsion between the two poles.

Not worrying about the actual technology that could do this, one can look at the maximal theoretical efficiency of interstellar travel: you could draw on your rest mass until your ship was essentially converted into a light beam of the same total energy. This would arrive nearly instantaneously at any destination in the universe. But you can't do this because you also need to conserve momentum. So the best you can do is have half your energy go into a light beam in the opposite direction. So there's the ultimate efficiency right there, not worrying about how you do it. You convert half the rest mass of your ship into light going one way, and half going the other. Then you go with the half going the desired way (as light energy, of course) until you get to your destination and reconstitute the energy of your ship back into rest mass (and you). There you are, no problem with energy or momentum, but you only have half a ship left. In your own rest frame, you might not experience anything all that bizarre, if you do this all gradually enough to keep the g forces down.

Somehow this hasn't made it into the discussion, but from this quote is appears that you believe that friction would be an issue. It wouldn't. There's no atmosphere in space to make it heat up. Now, if you plungued into the earth's atmosphere without decelerating first, that would be a different story.

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If aliens space faring civilizations are able to warp space so to speak, then who knows

Yep! Warping space-time is the way to go.
The minimum one percent scenario supposes 10000 space traveling species that maybe tens of thousands of years ahead of us.
But don't forget that oxygen is a very poisonous gas. And the fact that we have evolved with mitochondria in our cells to cope with it doesn't mean that other species have. All biological entities here are very specific to there enviroment. So it is reasonable to expect other species to have similar limitations.

Okay guys some of this is getting quite silly. And here is by far the silliest of them all.
Why you say?
Come folks think. If you could make propellant magically appear in your fuel tank, then you don't need a space ship to begin with. You could just make yourself magicly appear where ever you wanted to.

Here is another one almost as bad.

No you wouldn't. Even with the propellant's mass decreasing, you would still need to maintain your thrust to maintain your acceleration.
Because even though the mass of the fuel is decreasing, the mass of the ship is increasing as your velocity increases.
Shortly after achieving 3/4 of light speed, you will need to dramaticly increase your thrust to match your dramaticly increasing mass of the ship.

At 90% of light speed, the ship's mass will have increased to the point of it becoming impossible to produce enough thrust shipboard to continue acceleration.

This is as bad as the propellant magicly appearing.
If an alien species had this kind of technology, again they would have no need for a ship. They could simply have Scotty beam them to where ever
in the universe they wanted to go.

Come on guys we are getting even more wild then science fiction here.
Now your going to phase yourself between matter and energy. Where does all this end.

That is how it would seem to the traveller, but the actual passage of time would still occur. That 4.35 year journey to Alpha Centauri would still take no less then 4.35 years. By the time you got back, nearly 9 years, plus the amount of time spent at Alpha Centauri would still have elapsed.

I still think RocknReel would be farther ahead by making the opposition prove that aliens either are or have been here.

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Thanks for turning down the volume. Now I can hear the voices in my head again.

THANK YOU! I was trying to explain this earlier to Jeff Root but he insisted that acceleration was relative and that the accelerating starship could maintain a constant thrust with a constant acceleration all the way to light speed.

I just wanted to see if anyone else lept in and confirmed my layman's explanation of relativity. I didn't want to seem like a jerk.

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