MigL

As I was the one who made( what I thought was ) lighthearted comment about rednecks and anal probing, I feel I should respond, Would an alien civilization that possesses technology to travel the stars, and that doesn't want to be detected, not have some sort of visual stealth technology, or at least, radar stealth technology, like we already have ? Maybe we should then stick to more probable terrestrial phenomena. And I know you're feeling a little 'ganged-up' on, and maybe getting a little irritated,but I think you missed the point of Dimreepr's post. There are similarly many unexplained phenomena which some people attribute to ghosts. that these phenomena actually involve ghosts is equally unlikely. Or are you suggesting we should also investigate ghosts, as they remain unexplained ? With respect to US military ( DARPA ) secrets, in the 1980s the military began investigating stealth technology that eventually resulted in the L-M F-117/F-22/F-35, and the N-G B-2/YF-23/B21. These involved demonstrator projects, and since stealth tech was in its infancy, it involved crude, almost non-flyable shapes that were optimized for as much stealth as they could get. The L-M Have Blue demonstrator had a diamond shaped planform, with all angles optimizwd for least reflection, and would have been unflyable if not for computer-controlled fly-by-wire. The N-G Tacit Blue demonstrator had an inverted bathtub shape to the fuselage, but normal wings/control surfaces, as N-G was interested in the flying wing/blended body approach to their B-2 design. Both are now declassified, and you can google pics of both. I wonder how either of those would have looked to a crop-duster pilot who happened to spot one ? And would the military have admitted what it was ? Th

That only applies to drunk young men and desperate and dateless older ones who frequent those types of establishments, John. And yes, I've fit both descriptions a few times and many years ago 😄 .

I'm sure he'd be a lot more agreeable as to the value and purpose of Philosophy if he had the opportunity to chat with our own Eise.

No doubt. But in order to become an advanced civilization, they undoubtedly would have learned to prioritize their needs above their wants. Cost is not only a monetary issue; for all we know aliens don't use currency. But there are 'costs' in terms of resources, energy, and time that are not so easily discounted.

Not just one. There are many possibilities much more likely than getting hit by a meteor ( Ha Ha😄 ) Seriously. Propose as many as you like. Or the one you think will work best, or fits best with the data from UAP sightings. We can go through the benefits/problems involved with any method you propose, and hopefully we'll all learn something in the process.

Siince you involved me also, I had to read it too. The conclusion I came too is that lack of viable data does not give me reason to attribute an event to highly unlikely causes. I don't need a meteor to hit me on the head to reveal their existence, but if a rock hit me on the head, I would first look at the window above my head, or if INow is lurking nearby and throwing rocks at me. Those are way higher on the list of possible causes. Very well. Propose your method, because so far we have self-replicating probes, Alcubierre drive ships, solar sails, millions of VN nanoprobes, etc. All have problems. Suggest your method of choice, and we'll see if it is viable. Also include an effort/benefit analysis, as no one ( not even aliens ) would send a probe that returns nothing. We don't even go to the Moon anymore because of effort/cost; I'm sure an undertaking requiring effort/cost many orders of magnitude more has to provide some return. ( no one is going to send a probe into a Black Hole )

One problem I have with the central singularity. What happens when you apply Heisenberg's Uncertainty Principle to the singular event ( whether spatial or temporal singularity )? An exact location would mean indeterminate, even infinite, momentum, while an exact time would mean indeterminate, even infinite, energy. How would a particle, localized in such a way, remain trapped within the Event Horizon ? Now make that argument for all particles ingested by the BH and you have a BH which cannot exist. IOW, the singularity renders the theory inconsistent; either a singularity cannot exist, or Black Holes cannot exist. Yet we have photographic evidence of Black Holes, so where does that leave us ? I would be interested in a link to this article also. I'm interested in the proposed method ( pressure or force ) used to resist gravitational collapse at this radius.

I like indulging nice guys, Moon, so I'll start us off. Consider a constant acceleration ship, say 1g, for the confort of the occupants. "From the planetary frame of reference, the ship's speed will appear to be limited by the speed of light — it can approach the speed of light, but never reach it. If a ship is using 1 g constant acceleration, it will appear to get near the speed of light in about a year, and have traveled about half a light year in distance. For the middle of the journey the ship's speed will be roughly the speed of light, and it will slow down again to zero over a year at the end of the journey. As a rule of thumb, for a constant acceleration at 1 g (Earth gravity), the journey time, as measured on Earth, will be the distance in light years to the destination, plus 1 year. This rule of thumb will give answers that are slightly shorter than the exact calculated answer, but reasonably accurate." From Space travel under constant acceleration - Wikipedia We can then make other quick estimates to travel time "From the frame of reference of those on the ship the acceleration will not change as the journey goes on. Instead the planetary reference frame will look more and more relativistic. This means that for voyagers on the ship the journey will appear to be much shorter than what planetary observers see. At a constant acceleration of 1 g, a rocket could travel the diameter of our galaxy in about 12 years ship time, and about 113,000 years planetary time. If the last half of the trip involves deceleration at 1 g, the trip would take about 24 years. If the trip is merely to the nearest star, with deceleration the last half of the way, it would take 3.6 years." Now you might say"That's not too bad.". Only 113 000years pass on their home world to send a ship 100 000 light years. And a relatively short time to send it to a nearby star. Even doubling that time for two-way journey seems reasonable. Now comes the hard part. ( and I'm not going to attempt to quickly find/perform the calculation; I'll leave it to better, more fastidious, minds than mine ) How much Hydrogen do you need to carry, or collect along the way, in order to sustain a fusion reaction capable of sustaining a constant 1g acceleration/deceleration ?

Correct. We know of no force which can resist gravity once Neutron degeneray is exceeded in a neutron star, This is according to GR and QFT. Both of which have specific areas of applicability. When outside those areas they 'fai' by throwing up infinities; like at the center/future of a BH. IOW, points of infinite density are non-sensical predictions of badly applied models/theories. Also keep in mind that the central singularity, while being the event where geodesics end ( akin to latitude/longitude at the Earth's poles ), is not a location in space, but an event in time, and an infalling observer would be 'running into other stuff' at the end of time, not at the center. X-posted with others

You're taking that a bit too far. Aliens who are just like us, would require those things, but life, any kind of life, has some basic universal needs. It would need an energy/food source and to reproduce; that is all. Further, any life that emerged through an evolutionary process, would tend to optimize conditions to satisfy those needs. Their motivations, and decision making, would be based accordingly, and I don't expect that to change, even for a civilization that has been around for billions of years. But you are right. There is a slim possibility it could be ET aliens. Or time travelers, ghosts, fairies and leprechauns. But when that trivial possibility is many orders of magnitude less likely than a 'hubcap thrown in the air', it's probably OK to discount it. As to the technological obstacles to alien visitation, the Fermi Paradox/Drake Equation would have us inundated with alien civilizations, most of which should be much older than our relatively young one. Yet none have made definitive contact. You would think at least one would have, even if others are just playing hide-and-seek with us. Do you think maybe that means technological obstacles to interstellar travel are not easily dismissed ? Or maybe they're too busy with concerns about energy/food sources and reproduction, to send Von Neumann probes to other star systems to gather information which they may never recover.

The 'end of life' scenario of a Black Hole is complicated, as it is based on semi-classical/quantum assumptions by S Hawking and later D Page. Calculations suggest a Black Hole ( Schwarzschild ) to be a net emitter of radiation at the current CMB temperature, it would be about the mass of the moon. From this point, the BH's temperature will increase dramatically, and its size would shrink from millimeter size until radiation is being released explosively. The mass is no longer able to contain the radiation, as it did when the BH was much larger. The actual 'shedding' of the Event Horizon would happen at microscopic scales approaching Planck, but this would happen almost instantly, as temperature ( and output mass energy ) increase exponentially. The Wiki entry on Hawking radiation Hawking radiation - Wikipedia more specifically, the section on Black Hole evaporation has a good explanation with simple-to-follow math

Energy and mass are equivalent properties of a system. IOW, a Black Hole can radiate away massless but energetic photons and lose mass. When the remaining mass is no longer able to support an Event Horizon, and it can be quite a large mass, it explodes back into normal space-time, with a gamma ray burst. There is a problem with this scenario, and it's at the forefront of research. A certain property of Quantum Mechanics dictates that information must be preserved. Black Holes, in effect, swallow information and randomize it by re-emitting it as non-specific Hawking radiation and a final gamma ray burst. So we know we are missing vital knowledge about the process. This is likely because S Hawking's theory was a 'crude' combining of GR and QM; a self-consistent Quantum Gravity model is needed. ( and ther are questions as to whether that is even possible )

The most basic purpose of life, any life on any planet, is to reproduce. I can see generational starships spreading a race through an area of our galaxy, or even probes that deliver embryonic life to other star systems, but what is the purpose of your Von Neumann probes ? They can't gather and return information to the sender, as that would take twice as long as the journey to get here. So why would any advanced civilization undertake such a project that may return information outdated by millennia, or not return any at all. For any civilization to advance to a level of interstellar travel, they would need to use concepts like effort/benefit analysis, otherwise they would have made stupid decisions, and not advanced to such a level. And sorry, but sending probes that don't return information, or return it 10 000 years out of date, seems like a stupid undertaking to me. The second part of your post reminds me of the time travel problem ... "Time travel is impossible because no one, from a future where they have time travel, has ever been seen." For all you know, your UAPs might be from the future, instead of from other star systems; how would you differentiate between the two ? And why do you consider one choice more likely than the other ?

I didn't want to get in on this, simply because serious discussion lends 'credibility' to the UFO are aliens argument. There are many things that are inexplicable, and the vast majority are not even related to UAPs. And just as with the 'alien visitation' believers, there is an even larger group of people who are sure they know the reason for this larger set of unexplainable phenomena. You yourself, Moon, would call these people religious fanatics, and you'd be the last person to point out a need for scientific research to investigate God. The fact that something is currently inexplicable does not grant freedom to 'make up' a cause. And as with religion, this is my opinion. Given the physical limitations on travel between star systems, I really cannot understand the reasoning ( and expenditure of resources ) why aliens would visit us, play cat and mouse games, and anally probe a few hicks in the Southern US 😄 ( sorry, I had to throw that in ).

You're preaching to the choir. I suggest you fly to Moscow and tell Vlad to stop targeting the reactor in Zaporizhzhia, and the containment in Chernobyl with missiles, shells and bombs. Oh wait ... I forgot, some people don't follow the rules. Remember what Batman said "My parents taught me a different lesson ... dying for no reason at all. They showed me that the world only makes sense when you force it to."

Attraction is a mental phenomenon. Birth control pills are a hormonal modifier. A little knowledge dispels many rumors.

Viruses are kept around to study and develop vaccines and outbreak mitigation methods. Even if you get rid of all smallpox virus, there is no reason why a member of that strain couldn't mutate into something even more virulent than smallpox. Hope for the best, but be ready for the worst; IOW be prepared.

No feelings were hurt, and no need for apologies. I was in a 'mood' that day, for other reasons. Sometimes I get into a funk thinking I've outlived my usefulness in this forum, but I never feel bad about things said on an on-line forum. You guys aren't real, just imaginary anyway, right ?

The fact that you ignore my points make me feel you were just wasting time before also. Of course it is; it's in the thread title -why did Truman use the atomic bomb on Japan- The pChemical plant where I work makes and purifies liquid Phosphine. On a regular basis we may have up to 60 000 lbs of Phosphine at 700 psi, on site. That is considered a weapon of mass destruction, even by the FBI, who have been here to investigate our site after 9/11. What we consider weapons of mass destruction would have first been used in WW1, in the form of Chlorine and Phosgene gas attacks. It might also be relevant that certain battles of WW1, and even the Crimean war, regularly had 100 000 casualties; if not from munitions then from infections of wounds afterwards. even earlier when city states in Europe were besieged, flaming catapults may have killed half their inhabitants ( or plague-ridden rats, most of them ). In that historical context, would that have been considered use of WMDs? Or how about when Ghengis Kahn raided central Asian cities, killed most, enslaved the rest, and burned the city to the ground ? Does that make arrows and fire WMDs? If the taking of lives is immoral, Taking them to save economy and culture are also. I, and I'm sure many others ( even MSC ) don't consider taking the life of someone who is threatening the life of others, immoral. Fear is never a justification; an imminent threat is. There is a difference, and its usuaslly called self defense. Have I addressed all your points, or are you still wasting your time.

Aw, come on. Don't tell me you can't tell the difference between Eichmann saying "It was my job to put those Jews to death because we hate their kind.", and a cop saying "It was my job to shoot that person because he was about to kill another person.". President H Truman was trying to save American lives. You don't think that's a President's job ?

I think we can all agree that killing is immoral. I don't follow the reasoning where killing a few is more moral than killing many. And if so, how many ? And I find it strange that you think someone like President H Truman shouldn't value 100 000 American lives more than 100 000 enemy combatants. That is his job; to defend people he cares about. Oh, and I got 'pissy' like this because MSC commented about my morality, or lack thereof, not to simply be provocative.

This thread has devolved into an argument about 'morality', and 'mine is better than yours'. I don't need to justify my morality to anyone on a science forum; people dying are people dying, and and my morality says if you can save those you care about, you do what you need, up to and including nuclear weapons. Nuclear weapons are simply a better more efficient weapon for killing. So were knives and swords to people with sticks; did anyone complain about the morality of using them ? So were bows and arrows to people using knives; who complained about the morality of their use ? The same for guns, tanks and bomber planes.; why is it all of a sudden about 'morality' ? And why is it more moral to kill someone( or many ) with guns, or bombs, but not nuclear weapons, @MSC

Black Holes have entropy, and therefore, temperature, This temperature is inversely proportional to its size. A solar mass Black Hole has a temperature 60 Billionths of a degree K. All other Black Holes are even colder. That means almost all Black Holes larger than a solar mass are net absorbers of mass/energy ( the CMB is at 2.7O K ) I would think that this Black Hole involved in the collision is a relatively 'new' Black Hole that hasn't been very 'active' ( injesting mass/energy ). Maybe Mordred can shed some light on this; I believe it's in his 'back yard'. As Black Holes evaporate they get smaller and hotter, and radiate copious amounts of energetic radiation ( possibly encoding information ? ) before they lose their Event Horizon and explode back into normal space-time. This can only happen far in the future when the universe has cooled enough for stellar Black Holes to be net emitters of radiation, or, if primordial microscopic Black Holes ( formed in the high energy densities shortly after the Big Bang ) are reaching the end of their lives, None have ever been detected. My thinking has aklways been that no paticle can be constrained to a point, because that would imply ( By the Heisenberg Uncertainty Principle ) that its momentum ( and speed ) could be infinite, and it could escape the Black Hole. So I, and most people don't believe a central singularity is possible; it simply means our theory ( GR ) is not applicable at these energies and scales. I suppose this depends on your definition of 'theory' and 'hypothesis', but the theory does make some testable predictions.

Mordred is much more qualified to answer, but there is a difference between vacuum energy , and vacuum expectation value. My ( limited ) understanding is that while the concept of the VEV is a property of the vacuum which in Quantum field theory ( QED, QCD, Higgs ) governs virtual particles and condensation of fundamental masses, vacuum energy ( zero point or false zero ) is a property of the universe, and encompasses contributions made by virtual particles. The one place where the two 'meet up' is in regards to spontaneous symmetry breaking. Physicists are not like chemists ( no offence meant ). We are much more anal, and hate plugging numbers ( constants, fundamental or otherwise ) into equations. These numbers have to have a 'reason', otherwise we ask "Why that number ?", or have to invoke the observation selection effect ( anthropic principle ). So we try to derive these such numbers from 'first principles'. The usual method for vacuum energy is treating each point in space as a harmonic oscillator, summing over all such points and renormalizing the resultant infinity, usually with a suitable cut off, or ( as Sabine mentions ) that energy is a gauge condition where only differences are measurable. I believe there has been some research into using vacuum energy as 'effective mass' of the vacuum, or a field strength that 'resists' global curvature ( in GR ), to derive G from first principles ( like I said, we are anal 😄 ).

And a more, shall we say, controversial ( as always ) interpretation of vacuum energy