I'll try to explain why, and float my ideas past you.
One concept that hominids have speculated upon over the years is the concept of time travel. Can one "go back in time"? Or forward?
There is one way to approach this question, which, for me, casts a serious doubt on the possibility.
In the case of travel back through time, if it were possible, would we not be flooded with time travelers now? Shouldn't we be getting the accumulation of all people attempting it for potentially millions of years?
It's possible they have to follow some rules where they aren't allowed to interfere, but surely, some rogue person with bad intentions might get his/her self some time travelling technology. I suppose people in that person's future could try to stop it - but that'd create a paradox - the concept gets convoluted.
It's possible Earth is wiped out by some black hole before we figure that technology out, I suppose.
Overall, it's an interesting way to address the question - a Reductio ad Absurdum - pushing the proposed concept to its extremes and looking at what we'd expect to see if it were true.
Before continuing on, I feel the somber need to clarify some terms and concepts about propulsion.
The way I'll define it, there's three stages of propulsion.
Stage 1 - Newtonian Drives
Would it surprise you to know that the technology we used to send rovers to Mars is basically the same technology we've been using since we sat on a log in water and paddled ourselves along using a stick, tens of thousands of years ago?
We're still using the same exact principle - Newton's 3rd Law of Motion
Law III: To every action there is always an equal and opposite reaction: or the forces of two bodies on each other are always equal and are directed in opposite directions.Basically, we take a chunk of mass and hurl it behind us. We push off of it and we, ourselves, and thrown forward. We've been doing this same thing for thousands of years, from boats, to airplanes, to rockets.
Part of the problem is that, once outside of Earth's atmosphere - you have to carry all your fuel with you. Well, "Ram Scoops" and "Solar Sails" might be able to overcome some of that - but typically at many inconvenient costs.
Added to that problem is that a portion of the fuel you have to carry is used to merely overcome the inertia of the fuel you're carrying with you.
Let's say you're on a boat, and you're using cannon balls to propel yourself forward. For the sake of a point, I'm pulling some numbers out my ass here - but if you want 10 cannon balls worth of thrust, you'll need to carry 2 or 3 more to make up for the mass of the first 10. It begins to get absurd. If you want 10000 cannon balls worth of thrust, you may need to carry an additional 50000.
What we typically do when it comes to space travel is "shooting" the probes in a carefully calculated path, sling-shotting it around planets. Outside of orientation thrusters, our probes/satellites don't actually have any propulsion at all. They're launched using rockets and the rockets are then discarded.
It kind of gets the job done - but has severe limitations. At best, we can only bound from planet to planet, using them as "stepping stones"
Stage 2 - Non-Newtonian Drives
Once upon a time, when we wanted to light a room at night, we used candles or torches, or filled a hollow human skull with kerosene and lit it, or something. We'd set something on fire and ta-da! Light!
Thousands of years later, we figured out a new type of technology. We'd send electricity through it, and it produces light. We call them "light bulbs". They're drastically more safe and efficient than torches. If we had a solar collector, we could have light pretty much forever. Imagine how many candles it would take to do the same thing.
Instead of merely hurling mass behind us, the second stage Non-Newtonian Drives would generate a force in the direction of our choice, and require only electricity for input. Alternatively, we could call them "electric drives".
With solar collectors, or fusion reactors, etc, combined with electric drives, shuttling people back and forth between Earth and Mars would be considerably easier. We could accomplish higher speeds, we wouldn't need to worry so much about orbital positions or windows of opportunity - you just point the craft at the planet and punch it! Very little mass of the vehicle would need to be dedicated to energy storage (depending on the electric consumption of the drive, of course).
It would be revolutionary... might even make getting our butts to Alpha Centauri feasible... sort of. Maybe with multi-generational ships or cryogenics, we could do it. Although, plowing through the Ort cloud at 10% the speed of light might not be advisable.
Unfortunately, as of yet, we have no indications in physics that anything like this is possible.
Stage 3 - Faster Than Light (FTL) Drives
FTL drives are a broader category. It's basically anything that allows us to circumvent the speed of light limitation - whether that's warp drives (spacial compression), space folding, hyperspace, etc.
... none of which appear to be possible at the moment.
These drives would allow us to go from planet to planet, or solar system to solar system in human-tolerable periods of time. They may require significant energy requirements, but generally, they'd be what breaks us out of this solar system and into the depths of deep space.
To clarify for a moment my position on extraterrestrial life:
- From what I understand, extraterrestrial life is probably not just possible, but the universe is likely teeming with it.
- I don't, however, believe we've been visited by any here on Earth.
Part of the problem is hoaxes - there's so many of them, and typically the evidence is badly photoshopped photos, blurry video, testimony, etc. The whole question about alien visitation isn't all that different from considering the question of the existence of a god - the epistemology and standards of evidence of it. I see the same evidentiary failings with alien claims as I do with God claims.
So in short, I'm basically an skeptic in regards to alien visitation.
If it's shown that we are, then you may as well stop reading now, because the rest of my argument sort of depends on that being true. We'll consider that a hypothetical assumption from here on out.
Aliens and FTL - Reductio ad Adsurdem
Now that I'm done with a thousand pages of background context, here is the meat of my argument.
What if we figured out Non-Newtonian or FTL drives?
I'll tell you what we'd do. Probes!
We already have a lengthy list of extrasolar planets that we could explore. We as a civilization would likely have a renewed interest in space travel, and we could build a bunch of probes to go out cataloging planets. From radio transmissions to lights on the dark side of a planet (assuming we can't detect these until we're close), etc, it would be fairly straight forward to detect civilizations. Assuming we don't also have faster-than-light communication, we'd have the probes return to Earth to recharge/maintain/report, and then we'd send them our their way again.
We could then mount human expeditions to those planets.
It would be cool.
So why aren't alien civilizations already doing it to us?
One point to consider is that not all civilizations out there would be at the same technological level. Some civilizations may not exist for another billion years. Some may have be a billion years into their technological ages.
If Stage 2 and 3 propulsion were possible, we should expect that many civilizations out there would have mastered it by now.
Where are the probes? Where are the visits? (This is where the hypothetical assumption enters the equation)
We should be visited by all sorts of different civilizations. Surely one of them would have discovered us by now. Maybe they have, and they are just being quiet about it. Although, as many Sci-Fi movies base their storylines on, many of those alien races could be aggressive or unconcerned. We humans weren't that concerned when European explorers visited the new world. Why couldn't that happen between us an alien visitors? One of them may follow a "prime directive" not to interfere or reveal themselves - but all of them?
This is the reduction of the absurdity of the notion. What we'd expect is at least one visible visitor race. In fact, we should be visited by many.
Instead, what do we have? Blurry video? Drunk UFO pilots? Testimony? Why aren't any landing in Washington DC and trying to have a chat? Why aren't there any probes in orbit sending their version of our Voyager greeting?
It just doesn't jive.
Of course this isn't a disproof
There are lots of reasons why this could be.
- Maybe they just haven't found us yet
- Maybe they aren't as numerous as we thought (or none at all)
- Maybe it's inevitable that any space-faring race is going to buy into the non-interference notion
I don't know - but I'm pessimistic. Something's not right.
Alright, I'll back away from the conspiracy theory-esque thinking now.