>It predicted Mars more accurately than Copernicus did. The Earth centred universe fell more for socio-political reasons than scientific ones. It was long dead in the public mind before Kepler sorted Mars out.

Yes, but as you point out, the Ptolemaic model did not predict accurately the position of Mars. Neither did Copernicus, but that's beside the point. Kepler did, using elliptical orbits.

As for the earth-centered model being long dead in the minds of the public -- hardly. The "public" wasn't privy to such speculations. Those who were fought like dog for the most part against the heliocentric model. Ask Galileo, if you don't believe me. ;-)

In fact, to agree partly with you, the church hierarchy know they had to admit eventually that the heliocentric model was correct. They needed time, and Galileo at first agreed not to publish his telescopic observations that seemed to confirm a sun-centered model. He didn't keep his promise, and got into a lot of trouble for it.

Still, the baseline argument here stands. Scientific theories fail when they develop anomalies. (See Kuhn's _Structure of Scientific Revolutions_.)

As for the experimentation, oy, I hardly know where to start. The hypotheses are pretty complicated and numerous, and I have 4th graders arriving any minute now.

Try looking at the wikipedia article on interstellar travel for a list of the difficulties. They are numerous. It ought to provide sources that will lead you on a protracted trip through many articles in many physics journals.

It all comes down to e = 1/2MV(squared). It takes a lot of energy to to get to high velocities. Can't remember who, but one physicist calculated that it would take the entire energy output of human civilization on Earth to travel to even a close star like Alpha Centauri at only 4 ly away. And there surely isn't intelligent life that near to us by a factor of at least 10 or we would have detected at least the possibility of it (no systems with detectable planets that proximate to us).

Anyway, this really is my last post. In a way, I'm ruining things. It's fun to speculate, and here I am throwing cold water on the fun.

To answer the original question: It's a sign of the times that the question assumes that the aliens are harmful. We're back to the fifties red scare again. In less paranoid times, we have assumed that the aliens wanted nothing else but to help us or observe our odd, primitive ways. Our assumptions about aliens tells us more about ourselves and our frightful loneliness as a species than it does about the existence or non-existence of aliens.

But that's just my 2 cents. Frankly, I hope I'm wrong. It would be comforting to know that we aren't alone in the Great Void of the cosmos.

Stargazer

Edited by nerdboy52 on 04/15/2010 07:41:36 MDT.

"As for the other speculations, "folding space" sounds so fancy and scientific, but it merely refers to Einstein's notion that gravity is simply the bending of spacetime around a massive object: the more mass, the more bending, the more gravity.
Thus, when physicists speculate about "folding space," they are talking about folding very tiny sections of spacetime. In fact, in a sense you are folding the spacetime around you as you sit in front of the computer as your body applies its gravity to the surrounding space."

Excuse me, but when scientists talk about folding space they are seriously considering it as a means of interstellar travel. Imagine a piece of paper. You put a dot on either end. the theory is that the fastest, most direct course between points A and B is NOT a straight line. The fastest most direct route is if you are able to fold the paper over on to itself and bring the two dots together than THAT is the fastest, most direct route. Using that same example, but applying it to space, then one could travel instantaneously between worlds in two different parts of the universe. That is what JPL/NASA scientists have been working on for the last 10 or 12 years to solve the problem of intergalactic travel.

Another option is teleportation. Last year they have been successful in teleporting an atom. There is a long way to go yet, but scientists today, as we speak are working on it as a means of ultra-fast transportation in this world and across the galaxy. Again, I refer you to Harvard trained physicist Dr. Michio Kaku as one source. He also appears on a cable show called "The Universe."

Edited by socalpacker on 04/15/2010 15:57:01 MDT.

Beam me up Scotty?

Now to make things more complicated is a new hypothesis mentioned in Science Magazine that our universe is actually within a wormhole between 2 other universes. Supposedly unifies gravity, electromagnetism, & nuclear forces if memory serves. Would this have any bearing on faster than light travel?

The proponents of this hypothesis are at the dead end of a rabbit hole, and are going nowhere - faster than light, but still in the dark.

Here is one of my first proofs that they are here.

The three hares symbol has been around for a long time. Study it closely. Three hares. Each has two ears. Three times two equals six. However, count the ears - only three. Our reality is really illusion. These are the kind of mind tricks that space aliens play with humans. They know us better than we know us.


http://www.chrischapmanphotography.co.uk/hares/index.html


Three Hares Project

Oh, the aliens have been here for some time. People have seen them, at least in Europe, and recorded their impressions. Clearly however there have been visits from more than one species.
.

.
Cheers

Wikipedia has a very interesting article on the Fermi paradox.

Can't wait to see the look on Stagazer's face when he gets abducted and probed.

I for one welcome our insect overlords...

As for FTL... Alcubierre?

I know, I know- that's cheating. The exotic matter needed is prohibitively expensive, energy-wise. (On the order of what Thomas said for some of the other projects he mentioned.)

I await my photo of Rog standing on his doorstep as a lukewarm North Sea laps at his toes, screaming "Global warming is a plot by greedy scientists!"

Let's see YOUR data that faster than light travel IS possible, Rog. Fair is fair... :o)

I will admit that I keep my mind open an this one, though. Newtonian physics was the bomb, until Einstein. Who's to say that some future model won't be JUST A LITTLE BIT BETTER, just as relativity was just a little bit better than Newtonian physics? A Grand Unified Theory?Then, maybe we'll find a loophole.

But, yeah, under current models FTL is a non-starter.

The Fermi paradox has problems. It assumes that ancient cultures don't go extinct at a significant rate. What if the lifespan of intelligent races is very finite? Then we'd have to hope that one was nearby at the moment, and we haven't been looking very long.

Still, it's a fair question.

I read a decent story once that adressed Ben's concerns about broadcasting into space. The Earth was eventually destroyed when Von Neumann machines from an alien race dropped a slug of neutronium and a slug of antineutronium into the Earth. They orbited the core until drag slowed them down and they met in the center. (The antineutronium was so massive that relatively little mass was lost to interaction with the Earth, but it gave off LOTS of radiation.) Boom. No Earth.

But the sequel was even better. It centered around a group of humans out searching the local region in relativistic spacecraft looking for the perpetrators. Eventually they found them, but they had protected themselves well. The planet-killers had uploaded themselves into computers and were no longer material, but they had engineered a sentient race that still lived in their home solar system, and that was INNOCENT. And to boot, the innocent race thought that the planet-killers were their gods. To wreak vengeance upon the planet-killers meant annihilating this innocent race, too.

Quite a moral quagmire...

But, of course, the humans just destroyed the planet, anyway, and to hell with the innocents.

Edited by acrosome on 04/16/2010 20:31:52 MDT.

Faster than light is easy. You just start at a speed faster than light. No problem with reaching it. You are there already. The focus becomes all about having really, really good reliable brakes.

Not really practical, though, George. We aren't travelling faster than light. Ergo, we can't travel faster than light.

I want to know how to get to Sigma Draconis in my lifetime.

And on THAT subject, FTL might be a bust, but relativistic spacecraft aren't. (I can't tell you how bummed I was when I found out that the math for ramscoops didn't jive.)

Edited by acrosome on 04/16/2010 20:36:07 MDT.

http://www.youtube.com/watch?v=tSk51Lp-vHU

So assuming these aliens have the technology to travel to earth, imagine how light their packs must be back home. We are talking some featherweight shelters and some awesome looking sporks, no?

I don't think they carry gear. When they get to camp, they just have their stuff beamed down to them.

I fear we may be stuck with being smart chimps lost in space for a bit longer. However every year physics just seems to get weirder, so nothing would suprise me. Maybe contact will be telepathic, maybe from another universe/dimension altogether. To say it's just not going to happen because of x and y just seems a little premature to me.

Indeed some people are predicting government disclosure this year and 2012 isn't far off :). But I will say no more on this, as it makes some people pretty crazy :o.

Hi Dean

> We aren't travelling faster than light. Ergo, we can't travel faster than light.
Unfortunately, while I can understand what you are saying, I can't see any logical foundation for it.

Anyhow, one solution to the whole problem revolves around the concept of velocity and 'travelling'. Once you break away from the concept of 'velocity' it gets interesting. What does this mean? 'Velocity' usually means that you go through each point between A and B. Fair enough.

But what if you can find some way of moving from A to B without going through all those intervening points? Then the concepts of velocity and relativity cease to be relevant. There are no known laws of physics which prohibit doing this. How does one do this?

"Any technology sufficiently advanced ..."

Cheers

With the recent research into the idea of a holographic universe more and more our concepts of what connotes "reality" are being challenged. This talk here of "working with what is real" doesn't take into account the reality we live in everyday... our insubstantiality on an atomic level, for instance. Just because we can't see it doesn't mean it doesn't exist. The very act of refusing to open our minds to the improbable limits our ability to see beyond our conventions of "what is". We know so much less than we can even imagine.

To answer the original question: It's a sign of the times that the question assumes that the aliens are harmful.

Carl Sagan mused that if any civilization had managed to pull itself together enough to overcome war and bridge the enormous gaps between the stars then they must already have learned how to coexist in peace. A war faring civilization could never keep from tearing itself apart over such distances.

Edited by butuki on 04/17/2010 02:17:57 MDT.

@Roger-

"Unfortunately, while I can understand what you are saying, I can't see any logical foundation for it."

Wow. Then you're really not grasping the physics. You are an engineer, right? Or, more likely, you missed my point about 'under current models'.

My point ws that a particle that is sub-luminal can't cross that lightspeed barrier, so unless we are already travelling faster than light- which we are not- we can't travel faster than light.

Show me a superluminal particle. There are others looking for them, after all.

Anyway, as I said, I'm keeping my mind open too, and waiting for a mature GUT. There may be a loophole in it.

And, actually, we already know several loopholes. The PROBLEM is that they all require effectively infinite energy...

@Miguel-

Godwin in 5... 4... 3... 2... 1...

I don't buy Sagan's hypothesis (He was quite an idealist.) I see no reason why a hostile civilization couldn't be technologically advanced. It just has to be one of their priorities. Imagine if the Nazi's- a very technophile regime- had taken over the world. Don't you think that the human race would have landed on the moon a decade earlier, and have outposts on Mars today?

A more interesting idea is that as technology advances perhaps the natural tendency is for civilizations to get too big for their britches, so to speak, and accidentally kill themselves off. The hullabaloo surrounding the Large Hadron Collider comes to mind. Or, what happens when Al-Qaeda or some other wingnut group gets their hands on a relativistic rock? When near-luminal velocities are achievable no planet is safe.

Edited by acrosome on 04/17/2010 09:49:18 MDT.

I don't buy Sagan's hypothesis (He was quite an idealist.)

It's just as easy to say, "Well, I don't buy your hypothesis." To me Sagan made a lot of sense. I think he had a rare ability to visualize just how big the universe really is.

I happen to like idealists. Realists are the ones who take a fun thread and turn it into a debate, without seeming to get the point of the fun in the first place. (something I've been guilty of numerous times!)

But I think we have nothing to fear... Franco's fleet of Moments will more than match the prowess of those twirling saucers...

Hi Dean

> Wow. Then you're really not grasping the physics. You are an engineer, right?
> Or, more likely, you missed my point about 'under current models'.
:-)
Actually, I am a consultant research scientist with BSc, MSc and PhD in Physics. You can safely assume that I am reasonably familiar with the current state of play in most relevant areas.

> particle that is sub-luminal can't cross that lightspeed barrier
What Relativity actually says is that you cannot accelerate a particle up to the speed of light without infinite energy. It says nothing about speeds 'above' that of light, nor does it say anything about other means of getting from A to B.

Cheers