Is there life in the universe, and if so has it visited Earth?

[D H]

I keep finding the words, 'The basic scientific principle that everything is possible until proven not.', and I cannot help but consider it accurate.

Pearl S. Buck was not a scientist. You can find some very pithy statements about the impossible by politicians, philanthropists, writers, and scientists. You can even find mathematicians who recommend thinking of six impossible things before breakfast. You will not find something stating that "everything is possible until proven not" is a basic scientific principle.

 

[Hanfonius]

Pearl S. Buck was not a scientist. You can find some very pithy statements about the impossible by politicians, philanthropists, writers, and scientists. You can even find mathematicians who recommend thinking of six impossible things before breakfast. You will not find something stating that "everything is possible until proven not" is a basic scientific principle.

I had never heard of Pearl Buck - I guess this shows a local of formal education!

OK, so the offending words here are 'basic scientific principle'. If semantics can be bent slightly, and another phrase inserted to substitute three words, do you consider my assertions to be valid? Perhaps 'The enquiring mind will consider everything possible until proven not.'?

 

[vivesdn]

what would have been, not what is.
If 10 years ago (the cave was discovered on 2000) one crazy scientist would have said that 10m crystals were possible, I'm sure you would not assumed a probability of 1.

By the way, if the probability of an event is not zero, you cannot say that it was one just because it happenned.
I mean that the probability to get one specific side of a coin is 1/2. And when you got one of the possibilities, that event had still 1/2 of having occurred.

 

[CEL]

what would have been, not what is.
If 10 years ago (the cave was discovered on 2000) one crazy scientist would have said that 10m crystals were possible, I'm sure you would not assumed a probability of 1.

By the way, if the probability of an event is not zero, you cannot say that it was one just because it happenned.
I mean that the probability to get one specific side of a coin is 1/2. And when you got one of the possibilities, that event had still 1/2 of having occurred.

Wrong! The a priori probability of getting a tail when tossing a coin is 1/2. If you toss a coin and get a tail,the a posteriori probability of getting a tail in that trial is 1. It does not change the a priori probability for the next toss, that is still 1/2.
The probability of finding 10 m crystals in any cave on Earth is 1, since those crystals have been found. The probability of finding similar crystals in another place is nonzero. I cannot calculate what it is, since I am not a mineralogist.
The probability of life existing in the Universe is 1, since we know that life exists on Earth. The probability of life existing elsewhere is nonzero. Even not being an exobiologist, I would say that it is somewhat high.

 

[gareth]

Wrong! The a priori probability of getting a tail when tossing a coin is 1/2. If you toss a coin and get a tail,the a posteriori probability of getting a tail in that trial is 1. It does not change the a priori probability for the next toss, that is still 1/2.
The probability of finding 10 m crystals in any cave on Earth is 1, since those crystals have been found. The probability of finding similar crystals in another place is nonzero. I cannot calculate what it is, since I am not a mineralogist.
The probability of life existing in the Universe is 1, since we know that life exists on Earth. The probability of life existing elsewhere is nonzero. Even not being an exobiologist, I would say that it is somewhat high.

According to the findings of quantum physics, is there not a non-zero probability that everything will occur? It's just a matter of time, whether we're still around to witness the event or not is a different matter.

This has got me to thinking though, someone mentioned something a few posts back about imagining something that is not possible.

I find this hard. Our thinking and perception of things is built from our daily experiments (life), so this is all we can imagine. We live in a 4D world, how can we imagine something that is not possible if we have no experience of it. It's like trying to imagine living in a 10dimensional universe, you simply can't.

So how can we imagine something that is not possible? The thing must be built from our prior building blocks of knowledge (time, space, matter) anything we imagine will just be a certain arrangement of these elements which has a nonzero probabilty of happening.

So not only is everything possible, but things are possible that we can't even possibly comprehend.

 

[DaveC426913]

Dolphins, chimpanzees, and crows are all very smart, but do they qualify as "intelligent life"?

Dolphins and chimps are mammals, just like humans. I would categorize intelligence as a trait of the mammalian order. I would count that as a single instance of the rise of intelligence.

Birds, OTOH, are a second instance.

 

[DaveC426913]

I keep finding the words, 'The basic scientific principle that everything is possible until proven not.', and I cannot help but consider it accurate.

It is certainly commonplace these days, what with 'Power of Attraction' and other such woo-wooism rampant these days.

But it has nothing to do with science.

 

[Hanfonius]

I find this hard. Our thinking and perception of things is built from our daily experiments (life), so this is all we can imagine. We live in a 4D world, how can we imagine something that is not possible if we have no experience of it. It's like trying to imagine living in a 10dimensional universe, you simply can't.

So how can we imagine something that is not possible? The thing must be built from our prior building blocks of knowledge (time, space, matter) anything we imagine will just be a certain arrangement of these elements which has a nonzero probabilty of happening.

So not only is everything possible, but things are possible that we can't even possibly comprehend.

This is so thought provoking. Our building blocks of knowledge are growing rapidly each generation, and this must serve to increase our scope of imagination. This is where the science fiction writers dwell - but much of what they imagined has become reality. Perhaps just around the corner, we will discover anti-gravity, matter transfer, warp drive, free and clean energy, even perpetual motion.

Many of the young people entering into the sciences today will be fortunate enough to work within fields way beyond what we think of as impossible dreams.

 

[Ivan Seeking]

We have to be careful when we consider possibilities, as opposed to known violations of the conservation laws, causality, etc. For example, there is no reason to believe that a perpetual motion machine would ever work because we have well tested theories that tell us why they don't. But, might it be possible that some unknown effect or phenomenon could appear to be perpetual motion? Could something fool us for a time before we began to understand it? I don't see how this can be ruled out. But, we would still expect that energy is conserved over the entire system.

Unlike a perpetual motion machine, the existence of which would violate the known laws of physics, the WARP drive foks are trying to exploit known physics to discover loopholes, if you will, that might allow us to work around limits that were only assumed to be absolute. And while other complexities may arise that makes the idea WARP drive implausible or impossible, the idea itself is not one that assumes a magical solution from the netherworld, as does the notion of a perpetual motion machine.

 

[gareth]

We have to be careful when we consider possibilities, as opposed to known violations of the conservation laws, causality, etc. For example, there is no reason to believe that a perpetual motion machine would ever work because we have well tested theories that tell us why they don't. But, might it be possible that some unknown effect or phenomenon could appear to be perpetual motion? Could something fool us for a time before we began to understand it? I don't see how this can be ruled out. But, we would still expect that energy is conserved over the entire system.

Unlike a perpetual motion machine, the existence of which would violate the known laws of physics, the WARP drive foks are trying to exploit known physics to discover loopholes, if you will, that might allow us to work around limits that were only assumed to be absolute. And while other complexities may arise that makes the idea WARP drive implausible or impossible, the idea itself is not one that assumes a magical solution from the netherworld, as does the notion of a perpetual motion machine.

Yes, the conservation laws etc. are our (current) reality. Can we imagine a perpetual motion machine? (the one Lisa makes on the Simpsons usually springs to mind)

What I'm really asking is can we imagine breaking one of our conservation laws? A machine that spins faster and faster? Easy to imagine, but the science behind it is currently unimaginable. That's why we still fill our cars with dead fish.

 

[CEL]

According to the findings of quantum physics, is there not a non-zero probability that everything will occur? It's just a matter of time, whether we're still around to witness the event or not is a different matter.

I am not an expert in quantum physics. Where does it state that everything has non-zero probability of happening?
Anyway, even if something has a non-zero probability of occurring, this does not guarantee that it will occur sometime.
Remember that the Universe will not last forever. First it will cool down, then the black holes will evaporate and finally the protons will disintegrate. This will take around 10^{80} years. A very long time, but not infinite.

 

[Ivan Seeking]

Yes, the conservation laws etc. are our (current) reality. Can we imagine a perpetual motion machine? (the one Lisa makes on the Simpsons usually springs to mind)

What I'm really asking is can we imagine breaking one of our conservation laws? A machine that spins faster and faster? Easy to imagine, but the science behind it is currently unimaginable. That's why we still fill our cars with dead fish.

There are some funny things that happen at the quantum level [and in places like black holes] but these do not generally extrapolate to the normal, macroscopic world around us. As for some of the strange stuff that does in principle extrapolate from the quantum realm to the macroscopic, as is mentioned in the post above, the scales of time involved make it unlikely that such an event would ever be observed over the entire life of the universe. And even then, if some strange event did occur at large scale, it would only be once. So the short answer is no, we do not expect violations of the most basic principles - the conservation laws. Instead, we seek to expand our base of knowledge using what we already know, with reasonable certainty, to be true.

 

[WaveJumper]

I voted yes to the question whether intelligent has visited us, but there is something that boggles my mind. At least on 3 occasions I've seen fighter jets being scrambled to down said UFO's(belgian triangle comes to mind). What is with our military? Do we want a war we can never win? What if those said aliens used their super weapons and annihilated a part of the US or the whole of it? If they have enough energy to cross galaxies, it stands to reason that they might very well have capabilities to annihilate us. What gives us such tremendous courage to shoot missiles at something that could potentially destroy whole countries? I couldn't fire a missile at an UFO even if i had to go to jail upon landing. Do we have proof that what our fighter jets are trying to down, has done anything wrong or bad to us? What is the hostility for? IMO, we firing missiles at an UFO is like the tribesmen of the Amason throwing stones at helicopters. I would argue that if those were real highly technological space ships that we name UFOs, we are coming across as the laughing stock of the galaxy with the kind of weapons we are trying to use unsuccessfully on those rare encounters.

 

[Ivan Seeking]

By definition, the object is unidentified. The job of the AF is to protect the airspace of the respective country, and that's what they're doing. Also, often, it is only in retrospect that an encounter appears to be anomalous. In spite of the many conspiracy theories, the government probably doesn't understand the phenomenon any more than the rest of us.

I am also pretty sure that we've never downed an alien spacecraft , so if we are throwing stones, there appears to be no harm done.

 

[baywax]

By definition, the object is unidentified. The job of the AF is to protect the airspace of the respective country, and that's what they're doing. Also, often, it is only in retrospect that an encounter appears to be anomalous. In spite of the many conspiracy theories, the government probably doesn't understand the phenomenon any more than the rest of us.

I am also pretty sure that we've never downed an alien spacecraft , so if we are throwing stones, there appears to be no harm done.

A not so remote possibility is that these unidentified craft are man made and commandeered by the elite force of a scheming rogue nation with ambitions to control the entire human population.

If this is the case, these "ufos" are extremely vulnerable to projectile points (bullets) and so when you see gun laws prohibiting guns to most citizens, this is when the invasion is imminent. Canada has such laws and there are a slew of those floating tea saucers up here.

 

[Ivan Seeking]

A not so remote possibility is that these unidentified craft are man made and commandeered by the elite force of a scheming rogue nation with ambitions to control the entire human population.

I would debate that point in cases where the performance envelope of the intruder appears to be far beyond any human technology. We can't know the precise characterstics of the most advanced crafts, but we have a pretty good idea about the approximate limits of performance and technology. The Iran '76 event would be a good example - the first link in the UFO Napster. And being that this occurred over thirty years ago, we can have pretty good confidence that this was not a [earthly] technology from that time.

However, the AF responds because it is assumed that the UFO is a potential enemy craft, not aliens.

 

[Proton Soup]

I would debate that point in cases where the performance envelope of the intruder appears to be far beyond any human technology. We can't know the precise characterstics of the most advanced crafts, but we have a pretty good idea about the approximate limits of performance and technology. The Iran '76 event would be a good example - the first link in the UFO Napster. And being that this occurred over thirty years ago, we can have pretty good confidence that this was not a [earthly] technology from that time.

However, the AF responds because it is assumed that the UFO is a potential enemy craft, not aliens.

i just read the ufo00020.pdf, and everything about it screams 'unexplained electromagnetic phenomena'. maybe something like ball lightning. instrumentation/radio interference is repeatedly described as a function of proximity to the phenomenon. locals described noises like that of lightning.

 

[Chronos]

No compelling evidence [e.g., downed space craft] of alien visitation. Perhaps it is because interstellar travel is as prohibitively resource and time intensive as our own primitive science suggests. In that case, there may be billions of advanced civilizations in the universe that are just as stuck in their own neighborhood as us. That, to me, is the most logical explanation for Fermi's paradox.

 

[Ivan Seeking]

i just read the ufo00020.pdf, and everything about it screams 'unexplained electromagnetic phenomena'. maybe something like ball lightning. instrumentation/radio interference is repeatedly described as a function of proximity to the phenomenon. locals described noises like that of lightning.

Perhaps, and that is an explanation that I too have suggested, however it is not entirely consistent with the report.

 

[Ivan Seeking]

No compelling evidence [e.g., downed space craft] of alien visitation. Perhaps it is because interstellar travel is as prohibitively resource and time intensive as our own primitive science suggests. In that case, there may be billions of advanced civilizations in the universe that are just as stuck in their own neighborhood as us. That, to me, is the most logical explanation for Fermi's paradox.

Again, perhaps, but citing Fermi's paradox while denying the potential authenticity of alien spacecraft reports is a bit paradoxical in its own right.

 

[baywax]

No compelling evidence [e.g., downed space craft] of alien visitation. Perhaps it is because interstellar travel is as prohibitively resource and time intensive as our own primitive science suggests. In that case, there may be billions of advanced civilizations in the universe that are just as stuck in their own neighborhood as us. That, to me, is the most logical explanation for Fermi's paradox.

I'd say if they could get here they're here already and completely assimilated in a way that we can't see... like very advanced and efficient camouflage.

 

[CEL]

No compelling evidence [e.g., downed space craft] of alien visitation. Perhaps it is because interstellar travel is as prohibitively resource and time intensive as our own primitive science suggests. In that case, there may be billions of advanced civilizations in the universe that are just as stuck in their own neighborhood as us. That, to me, is the most logical explanation for Fermi's paradox.

It all depends of the longevity of technological civilizations. I believe that in the next century we will be able to find habitable planets in neighbor star systems.
If there is interest, colonizing expeditions could reach such planets in 10 to 20 years. With the head start in technology, such colonies could reach other star systems after one or two centuries and so on.
If our civilization lasts enough, in one million years we could colonize the Galaxy.
The fact that the Galaxy does not thrive with alien civilizations suggests that either we are alone or that civilizations don't last that much.

 

[DaveC426913]

The fact that the Galaxy does not thrive with alien civilizations suggests that either we are alone or that civilizations don't last that much.

The third possibility is that the galaxy is thriving but not in a way that's visible to us. The classic "quarantine" hypothesis.

 

[baywax]

I would debate that point in cases where the performance envelope of the intruder appears to be far beyond any human technology. We can't know the precise characterstics of the most advanced crafts, but we have a pretty good idea about the approximate limits of performance and technology. The Iran '76 event would be a good example - the first link in the UFO Napster. And being that this occurred over thirty years ago, we can have pretty good confidence that this was not a [earthly] technology from that time.

However, the AF responds because it is assumed that the UFO is a potential enemy craft, not aliens.

Yes, but completely isolated tribes in Brazil have no experience with a "performance envelope of (an) intruder (that) appears to be far beyond any (tribal) technology" when they see a helicopter buzzing them. I'd further this idea by saying 1. Developments since the first Foo Fighter (1933) may have gone beyond what we're used to... 2. Developments based on downed extraterrestrial vehicles may result in these "ufos".

 

[gareth]

The theories about the UFO phenomena been due due man made craft got me to thinking;

Science, and in turn technology is based on constantly buliding on other peoples work. Could there really be a research project (that would have to involve some pretty interesting stuff) be going on that is so big it has managed to engineer one of these crafts (if they are crafts of course)?

It would have to be very secret, and only known to a very select group of people. It seems unlikely that with all the mainstream science going on at the same time some of the ideas would have cropped up here and there.

Basically what I'm saying is, if we did build such objects, we got help.

 

[Ivan Seeking]

Developments based on downed extraterrestrial vehicles may result in these "ufos".

That gets into conspiracy theories, which are not appropriate for discussion here.

 

[baywax]

The fact that the Galaxy does not thrive with alien civilizations suggests that either we are alone or that civilizations don't last that much.

An historical and terrestrial example of a longer lasting civilization is Egypt which lasted 3000 years and they didn't make it to the moon but there are indications they were trading with South America. We could look at Egypt as part and parcel with the world civilization which has culminated in unmanned probes to Mars and golf on the moon.

 

[baywax]

That gets into conspiracy theories, which are not appropriate for discussion here.

Sorry... speculation acts as a magnet for loonies... (which are dollars in this patch of the woods!)

 

[baywax]

I have this urge to vote for Obama... must find polling station in Blaine...

 

[gareth]

I wonder will the US ever release their UFO reports like the MoD in the UK?

Maybe Obama will, who knows!

 

[Ivan Seeking]

We have probably thousands of U.S. Government files linked in the UFO Napster.

Files are released upon request through the Freedom of Information Act, but information still considered to be sensitive is blacked out. Note that information about the UFO is generally not blacked out; mostly just the names of individuals, the names of countries, etc.

Of course the tricky part is that you have to know a file exists before you can ask for it.

 

[Proton Soup]

That gets into conspiracy theories, which are not appropriate for discussion here.

good grief, it's no different than this religious belief of extraterrestrials zipping about the planet in crafts of pulsating light. Carl Sagan was bitten by this bug, too, despite no more evidence than wishful thinking.

 

[CEL]

An historical and terrestrial example of a longer lasting civilization is Egypt which lasted 3000 years and they didn't make it to the moon but there are indications they were trading with South America. We could look at Egypt as part and parcel with the world civilization which has culminated in unmanned probes to Mars and golf on the moon.

First of all, the Egyptian technology could hardly lead to self destruction. Our nuclear technology can.
Secondly, the presence of Egyptians in South America is speculative.
Third, for a civilization to spread through the Galaxy it will take millions of years. A tiny fraction of the life of the Galaxy, but a very long time for a civilization.

 

[baywax]

for a civilization to spread through the Galaxy it will take millions of years.

What makes you think that?

It only took a few minutes to "discover" fire and the wheel. It could take just as short a time to discover a way to "spread throughout the galaxy".

 

[CEL]

What makes you think that?

It only took a few minutes to "discover" fire and the wheel. It could take just as short a time to discover a way to "spread throughout the galaxy".

For all we know, and there are evidences of that, the speed of light is a limit. Since the Galaxy has a diameter of 100000 ly, it takes light that much time to cross the galaxy. An object with mass will take much longer.
And don't come with "warp drive" or something alike. We are talking about science, not sci-fi.

 

[baywax]

For all we know, and there are evidences of that, the speed of light is a limit. Since the Galaxy has a diameter of 100000 ly, it takes light that much time to cross the galaxy. An object with mass will take much longer.
And don't come with "warp drive" or something alike. We are talking about science, not sci-fi.

We are talking about unidentified flying objects that allegedly defy the capabilities of any conventional flying objects we know of. This would bring the use of wormholes, superposition and dimensional shifts into the realm of the possible "discoveries" a civilization could utilize.

 

[WaveJumper]

We are talking about unidentified flying objects that allegedly defy the capabilities of any conventional flying objects we know of. This would bring the use of wormholes, superposition and dimensional shifts

Being able to choose a particular state out of all possible states of a spaceship is a good idea for intergalactical travel, although i always thought it was the thing that we don't talk about on science forums that ultimately selects which future events will take place. Wouldn't that make us practically gods? Sounds too good to be true, but I'm not dismissing it as a means to an end, if we survive long enough, we might become something close to gods.

 

[DaveC426913]

We are talking about unidentified flying objects that allegedly defy the capabilities of any conventional flying objects we know of. This would bring the use of wormholes, superposition and dimensional shifts into the realm of the possible "discoveries" a civilization could utilize.

It's a bit of a jump, wouldn't you say, from merely
...maneuvering faster than 21st century human technology...
to
... spitting in the face of fundamental laws of the universe ...?

 

[Ivan Seeking]

Yes, no need to go off a cliff here. We can only speak to the alleged facts. If we can't readily explain an event, that doesn't justify unfounded speculation. Your vote in the poll was your chance to make a leap-of-faith statement.

 

[Ivan Seeking]

And don't come with "warp drive" or something alike. We are talking about science, not sci-fi.

To be fair, almost by definition, any technology had by a race of beings a million, or even a billion years more advanced than us, would be science fiction to us. And we do have some exotic ideas of our own.

https://www.physicsforums.com/showthread.php?t=204637
http://www.nasa.gov/centers/glenn/technology/warp/warp.html
http://www.ufoskeptic.org/JBIS.pdf

We just aren't in a position to speculate as to what idea if any might eventually be practical. We can only ask if all have been ruled out. If we find credible debate among experts, then clearly the case is not closed. Also, there is always the chance that somebody like Heim will come along and change the game.
https://www.physicsforums.com/showthread.php?t=106059

If you ask what technology we might possesses in a billion years, were "humans" to survive that long, you would also have to ask what species we would be, because we certainly wouldn't be remotely similar to modern humans.

 

[baywax]

It's a bit of a jump, wouldn't you say, from merely
...maneuvering faster than 21st century human technology...
to
... spitting in the face of fundamental laws of the universe ...?

For sure. My mistake. I'm not an MD or an astrophysicist but I know spitting is unsanitary and highly offensive. I'd never, in a million light years, spit on what you or anyone considered to be fundamental laws of any kind.

How can we explain objects "flying" at 1900 mph over Crawford, TX. And if we decide that they are extraterrestrial objects, how do we explain how they got to earth?

 

[gareth]

For sure. My mistake. I'm not an MD or an astrophysicist but I know spitting is unsanitary and highly offensive. I'd never, in a million light years, spit on what you or anyone considered to be fundamental laws of any kind.

How can we explain objects "flying" at 1900 mph over Crawford, TX. And if we decide that they are extraterrestrial objects, how do we explain how they got to earth?

I agree, there must be some mild spitting involved.

 

[CEL]

How can we explain objects "flying" at 1900 mph over Crawford, TX. And if we decide that they are extraterrestrial objects, how do we explain how they got to earth?

Any massive object moving in the atmosphere at such speed would cause an enormous sonic boom.
The fact that no such sound has been observed suggests that the "flying" object was massless. Probably an electromagnetic phenomenon.

 

[gareth]

Any massive object moving in the atmosphere at such speed would cause an enormous sonic boom.
The fact that no such sound has been observed suggests that the "flying" object was massless. Probably an electromagnetic phenomenon.

That's assuming the object is propelled by a known propulsion system.

 

[CEL]

That's assuming the object is propelled by a known propulsion system.

No, the sonic boom is caused by the movement of the object through the air. Even without propulsion an object moving that fast would cause the boom.

 

[gareth]

No, the sonic boom is caused by the movement of the object through the air. Even without propulsion an object moving that fast would cause the boom.

Ah yes, I did say known propulsion system.

The object is unidentified, therefore its mechanism for moving in space is unidentified.

Any attempt to guess this mechanism is purely speculative (quiet jet engine, warp drive, wormholes, extra dimensional travel...the list goes on).

You claim that the phenomena might be caused by electromagnetic effects, but I find this hard to visualise.

Shiny metallic discs darting around at Mach 3, showing up on radar and reported by several wintesses, that would be a pretty neat light trick.

 

[CEL]

Ah yes, I did say known propulsion system.

The object is unidentified, therefore its mechanism for moving in space is unidentified.

Any attempt to guess this mechanism is purely speculative (quiet jet engine, warp drive, wormholes, extra dimensional travel...the list goes on).

No matter what the propulsion system is. Any object moving through the air at Mach 3 will produce a sonic boom.

You claim that the phenomena might be caused by electromagnetic effects, but I find this hard to visualise.

Shiny metallic discs darting around at Mach 3, showing up on radar and reported by several wintesses, that would be a pretty neat light trick.

Electromagnetic phenomena can show on radar screens, since radar uses EM waves in detection and ranging (this is the meaning of the device: RAdio Detection And Ranging).
Visual witnesses are not reliable. Of course, if there are witnesses there should be made an investigation, but witnessing alone is not accepted in science and is accepted in a court only as additional evidence. If the police does a lousy job, no amount of witnessing will be accepted in court.

 

[gareth]

No matter what the propulsion system is. Any object moving through the air at Mach 3 will produce a sonic boom.

Again,

you are assuming the object is actually moving through the air and no other possiblity.

There might be some crazy physics going on which I am not going to speculate about (but I did mention briefly in my previous post).

I think military pilots reports are fairly reliable, but that's just my opinion.

 

[CEL]

Again,

you are assuming the object is actually moving through the air and no other possiblity.

There might be some crazy physics going on which I am not going to speculate about (but I did mention briefly in my previous post).

I don't believe in ghosts. If there was some crazy physics by which an object could move through the air without affecting it, it would be easier to make it invisible to radar.
With the well behaved physics we know it is possible to build stealth planes that are almost invisible to radar.

 

[gareth]

I don't believe in ghosts. If there was some crazy physics by which an object could move through the air without affecting it, it would be easier to make it invisible to radar.
With the well behaved physics we know it is possible to build stealth planes that are almost invisible to radar.

Define ghosts.

Who is trying to make it invisible to radar? There are a lot of UFO reports that show that these things aren't shy, and in some cases seem to go out of their way to be seen.

I guess all I'm saying is we don't know what they are, and for us to assume to know all the science behind the phenomena is just plain wrong.

Whether it being little green men, a modern artifact of the human mind, us from the future, us from the past, military toys, swamp gas, weather baloons, ball lightning or otherwise, we, the public, do not know what it is and should just keep an open mind about the science involved.