In a study published this week in the journal Science, scientists try to evaluate comet collisions with the Earth and whether they are the cause of mass extinctions
Scientists have debated how many of the mass extinctions in Earth's history were caused by comets or asteroids crashing into the ground. Most agree that an asteroid crash 65 million years ago ended the age of the dinosaurs, but there is still uncertainty as to whether other extinctions were also caused by the same cause.
In fact, astronomers know that the inner solar system was protected at least to some degree by Jupiter and Saturn whose gravitational fields can cause comets to be ejected into interstellar space or sometimes cause them to crash into them. The point was reinforced recently when on July 20th a huge spot was discovered on the surface of Jupiter, apparently evidence of a comet impact.
There are about 3,200 long-period comets known to scientists. The length of their orbit around the sun may range from 200 years to millions of years. Among the best known were Hale-Bopp, who was visible to the naked eye for most of 1996 and 1997, and who was one of the brightest comets of the 20th century.
Scientists also believe that almost all long-cycle comets that reach the inner solar system and cross Earth's orbit originate in the Oort cloud, remnants of the nebula from which the solar system was formed 4.5 billion years ago. The cloud starts at a distance of 150 billion km from the sun (a thousand times the distance of the earth from the sun) and stretches up to a distance of about 3 light years. The Oort Cloud may contain billions of comets, most of them so small and distant that they will never be observed.
The orbit of long-period comets may change due to the gravitational pull of a neighboring star (one of the Sun's neighbors in the galaxy) when it passes near the Solar System, and it was thought until now that these encounters may only affect the outer bodies in the Oort cloud.
It was also believed that the internal bodies of the Oort cloud could reach orbits that cross the orbits of the Earth only in the case of an extremely close passage of a star, which causes a shower of comets on the inner solar system, but it turns out that even without an encounter with stars, long-cycle comets from the interior of the Oort cloud can slip beyond the boundary of the protection of the solar system that Jupiter and Saturn place, and move towards the Earth.
In the new study, University of Washington researchers Nathan Cave and Thomas Quinn used computer models to simulate the evolution of the comet cloud in the Solar System over 1.2 billion years. They found that even outside the meteor shower period, the inner Oort cloud is a major source of long cycle comets that eventually cross the Earth's orbit.
By estimating that the inner Oort cloud is the only source of long-period comets, they were able to estimate the highest possible number of comets in the inner Oort cloud. The actual number is unknown, but using the maximum possible number, they determined that no more than 2-3 comets could have hit Earth during what is believed to be the most powerful comet shower in the last half billion years."
"For the past 25 years, the inner Oort cloud has been considered an unobservable region in the solar system and is full of mystery, and which can launch eruptions of bodies that sometimes exterminate life on Earth," said Kevin. "We have shown that the comets that have already been discovered can be used to estimate the altitude limit to the number of entities in this database.
Three major collision events occurred almost simultaneously. The scientists suggest that the small extinction event that happened 40 million years ago was caused by a comet shower. Cave and Quinn's research shows that if the relatively small extinction event was caused by a comet shower, then it was the most massive comet shower since the fossil record began.
"This tells us that most of the powerful comet showers caused minor extinctions and the other showers were less dangerous, so the likelihood that comets are the cause of extinctions decreases."
He commented that the study estimates the area surrounding the solar system has not changed over the course of 500 million years
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Well, point:
I think you are the one who is wrong but I have explained this issue many times (you can see in the links I sent Yoram Tomer and in Yoram Tomer's own words).
The words of Yoram Tomer and my words are well reasoned, while your words are only an unreasoned "final conclusion".
You did not rule out any reasoning from the reasons that came up and without doing so your conclusion simply does not follow from the facts.
I repeat:
1. A theory is a collection of axioms - agree or disagree? If not - explain what a theory is in your opinion.
2. The collection of axioms describing reality must include a description of the natural numbers (because of quantum theory). agree or not? If not - please explain how the natural numbers can be dispensed with.
3. Gadel's incompleteness theorem says that a consistent theory that includes a description of the natural is incomplete. agree or not? If not - tell us where Godel was wrong.
4. An incomplete theory is a theory that has legal claims of the theory that cannot be proven or disproved through logical developments based on the axioms of the theory. Here I will not give you an option of disagreement because this is the definition that Godel was talking about, so there is no room for him to innovate here.
5. It basically says it all. No physical theory will be complete. The only escape from this matter is the collection of considerations that I pointed out at the end of my response to Yoram Tomer. These are considerations that I brought up (me and not you) in the discussion with Adi, but these considerations only point to a certain possibility and do not prove that this is reality (even mathematically). They are simply based on something in the proof technique of an increasing theorem that leaves an opening for the possibility that it may or may not be true - all the axioms to be added to the theory is an infinite series of axioms, each of which asserts that the set of axioms preceding it is consistent. This is a consideration that deals exactly with the group of non-conclusive claims that his son grew up with, but there is no certainty that these are all possible non-conclusive claims.
Michael, first of all thanks for the interesting and pessimistic article by Hawking (who changed his mind)...
But I think he's wrong about a few things there:
*It's a shame that he changed his mind (certainly out of desperation after decades of effort), yes a theory will be found that will include gravity and quantum mechanics. (You need to stop with string theory, that's not where the solution will come from).
*After this model is found then it will be possible to start asking where Godel's incompleteness theorems come into the picture, (and not at the moment we don't have one model). And I still stand by my claim that Godel's theorems are not generally related to physics but to mathematics.
*For some reason he states that every theorem that cannot be proven in this physical model means predicting the future. How did he get there? In the mathematical models that Godel talks about, you can build any theorem you want, not just the first derivative of time (where everything can be proven).
point:
Regarding the relevance of Gadel's incompleteness theorem to physics - the great and the good disagree with you.
This includes, among others, Hawking:
as written Wikipedia
And here:
http://www.damtp.cam.ac.uk/strings02/dirac/hawking/
I didn't understand what you said about black holes.
No inaccuracies were found in the theory of relativity and the way in which all the scenarios (including the one you brought up) avoid infinity is by preventing (one way or another) the creation of zero distances.
Although it is true that every theory has a limited warranty, but that is not what we are discussing.
Regarding the "explanation of the framework" - I do not accept the things.
What do you think should constitute a framework and what is the theory?
Why, in your opinion, do some of the axioms (and a court of law won't help - a theory is a collection of axioms) deserve to be included in the theory and some are not?
Regarding the "disclaimer" from physics that depends on frames of reference, the expectation is that physics will explain the frame and not depend on it, and adding axioms shows that it is not a theory of everything (that explains everything) that we are looking for.
Yoram, really incompleteness theorems are not related to physics in general.
Michael regarding the important claim of black holes, the existence of tiny black holes is directly related to the physics of elementary forces and elementary particles. And if we do not know (and in fact we determine this only for reasons of convenience) the true model, then we should not complicate a scenario of black holes that were created only under the assumptions of that physics which is agreed to be an incorrect or insufficiently accurate model.
For example, one of the interesting results of string theory is the explanation that a black hole is a highly compressed structure of strings.
Yoram Tomer:
If you read the comments on these links you will see that I am fully aware of the matter.
This does not belong in my response to the point.
https://www.hayadan.org.il/insight-into-evolution-of-first-flowers-1306097/#comment-226040
https://www.hayadan.org.il/how-we-know-that-we-know-0803092/#comment-186286
https://www.hayadan.org.il/univese-on-tshirt-006081/#comment-57223
https://www.hayadan.org.il/univese-on-tshirt-006081/#comment-57223
incidentally:
I must point out that it is not entirely clear that the problem is real and not purely formal.
To understand my intention in this matter, read the discussion between me and Eddie starting with this response:
https://www.hayadan.org.il/impossible-conclusions-2306091/#comment-227233
to Michael Rothschild,
According to Gadel's incompleteness theorem, jumping axiom does not help to fully solve the model. As long as the number of axioms is finite there will always remain unsolved problems.
If we apply this statement to physical models, we will never be able to find a perfect model. It is possible that the search for a physical theory to explain the universe is futile. As Gedel based his theorem on the axiom of the natural numbers, so we can base the physical model on the axiom of the fact of our existence. Any model that tries to expand the study of existence by adding axioms will encounter unsolved problems.
Yoram
point:
I do not understand your last reservation.
A theory is a collection of axioms from which the rest is supposed to be derived.
If you say that the theory depends on the existence of certain things - all you have to do is add their existence as one of the theory's axioms.
The axiom you add in this way will not be worse than others.
point:
as you please.
Before I wrote my words I spoke with Professor Emeritus Gideon Alexander from Tel Aviv University and he shares my opinion.
Do you think elementary particles are black holes? As we know - if their radius is smaller than the Schwarzschild radius of their mass + energy - they must be black holes.
And another problem regarding all the physical theories that exist today (including the string theories), which are all theories that depend on the framework (the space-time/universe), while we would expect a theory that explains everything, that would not depend on any framework (that is, it would contain within itself what other theories see as a framework) , therefore it is hard for me to believe that string theory is really "correct".
Michael, I'm talking about the standard model where the particles have no volume, what you see in collisions is the volume of their effects (gravity, electric, strong, weak).
If the particles had volume (in some dimension), then what "matter/energy" would that particle be full of (and what does that mean)?
It seems to me that because the things do not really exist, then no such "material" will be discovered, although this is not binding.
Hello to Michael Rothschild.
Thank you for your quick, thorough and accurate answer. I actually received confirmation from you on what I understood you had achieved. This confirms my finding that there is no dimensionless entity.
I read and ponder a lot on the obviously philosophical questions of: "there is", "nothing", "void", "infinity", "before the big bang", "did space and dimensions exist 'before'", "was the energy of the big bang a being There is no end - it seems delusional", "Does the universe expand endlessly…….????". All of these are disturbing questions mainly for those who did not study physics, but studied mathematics with a modern analysis approach and especially with the question of divisor numbers versus a sequence and the fact that there are groups whose measure is 0 and whose strength is "a" and how all this relates to existence and reality.
And again, thank you from the bottom of my heart, and I would be happy to continue the dialogue between us. It is also possible by email ytomer@bezeqint.net Yoram
Yoram Tomer:
None of the theories speak of zero dimensionality. no one!
Strings are at least one-dimensional, but string theory also talks about two-, three-, and more-dimensional membranes (sheet sections).
Nor does traditional quantum theory speak of point particles.
We talk about zero-dimensional points only as a model that is an excellent approximation in many calculations, but the very possibility of causing particles to collide shows that these are entities with volume.
For some of them (fermions) this stems from Pauli's principle of prohibition and for others for other reasons.
Note (also a point) that if the particles were truly zero-dimensional - they would be black holes!
Yoram, you raise a correct and problematic point,
On the other hand, if the particles had a volume other than 0, it was necessary to describe what filled that volume, and then it was no longer elementary particles. Therefore, there are actually no particles, and there are only their effects (force field, mass, etc.).
Questions about the essence of existence, particles and strings.
After reading and sitting and reading about the "perceptual revolution" of string theory against particle theory, I am still stuck in the concepts, and I have a feeling that the scientists are wearing wrong images about physical essences. what's the matter?
First, according to my understanding, physics begins with existence and not in an infinite void. Every physical entity must have dimensions. According to my understanding, there cannot be a dimensionless "there".
String theory challenges the "particle" concept and asserts that particles have "zero dimensions" and strings have one dimension (length) moving in a four or multidimensional world ("open" string, "closed" string, "vibration" occur in multidimensional space. I tried to imagine the This discovery, and how it differs from the particle approach. The conclusion I reached, that the presentation of particles as "zero dimensional" entities is a mistaken concept. Zero dimensions means "nothing" any particle, no matter how small. It has dimensions. Naively, in the aspect of four-dimensional beings a particle It is a tiny "ball" that is "created" in the dimension of time and if it does not have 4 dimensions, it is outside the realm of existence. According to our perception of reality, everything that "exists" has at least three dimensions of space and the dimension of time. In the absence of one of the dimensions, the entity does not exist .
In summary: whether we stick to string theory or remain in the realm of particle theory, we are discussing four-dimensional entities - or more.
Maybe the text I wrote indicates that I am a physics teacher, but I would like to hear a reference to this topic.
Hugin,
Your exchange of names fails to hide the obvious fact that you simply need professional help.
The frequent comparisons you make to Nazis, your strange preoccupation with secretions and excretions ("no one can see the other, that 'you' especially shit on the truths"), the ugly language you use ("You will be recorded as a scumbag") do not indicate mental stability.
Unfortunately, the kind of professional help you need is not available on this site.
Please go to the right place as soon as possible, because it is obvious that your condition is deteriorating.
Indeed it seems so, because in the deleted response it's a good thing (it doesn't really respect her) she speaks in female language and once again made comparisons between anyone who doesn't think like her and the Nazis.
It seems to me that Lost is an impersonator.
to lose Hugin, maybe enough?
Lost:
Yes.
It seems to you.
Did it seem to me that we heard an alarm wail? Maybe the sound of backs being rubbed by the scales and excesses of idle thought or maybe the wail of a dragon that turned into a dragonfly that turned into a bubble that burst to the winds .. what was it exactly? Longing? Nostalgia?
Do you need to sign a certain "statement"? Just say and we will settle.
By the way, white blood:
The interpretation of the analogy in Avod's response as well as the interpretation of other mental phenomena in his recent responses is that he cannot overcome his "fairness".
If you've read comments in the past, you've probably noticed the garbage that's been sown here from the pen of Hugin/Quantus/Q/H and other names of high and low.
white blood:
In relation to the diversion of asteroids - I think the subject is pretty well exhausted in this article
and in the discussion that followed.
I don't know if this answers all your questions but I suggest you read it and then ask what's left.
I will only point out that in the gravitational shift method a weak force works and therefore it must be activated for a long time.
This is actually true for other diversion methods where you don't want to apply too much force because you are afraid that the brittleness of the asteroid will lead to its disintegration if a strong force is applied to it.
Regarding a barrage of asteroids - I tend to assume that such a barrage (if it deserves its name) consists of asteroids moving in close proximity to each other, so it is likely that they will all hit the same "target".
Lost:
Maybe I'm really dumb, but I didn't understand the meaning of this analogy you made between an asteroid and the Jewish people / gypsies, etc.
If you mean to say that in the eyes of the US, the Japanese were a danger, or in the eyes of Hitler, the Jews, Gypsies, Slavs, etc. were a danger - there is no connection at all;
The Nazis believed that the Nordic (Aryan) race was the supposedly superior one, and only it had the right to exist - this was their opinion only.
Japan attacked the USA at Pearl Harbor and thus opened a front. God forbid I do not justify the reaction, but this is a war between 2 countries, what does this have to do with all of humanity?! Again, here too the Japanese were an enemy of the USA, only theirs.
An asteroid is a lifetime hazard on Earth; Both for the Jews and for the Nazis and for the Muslims and the Christians and the seculars and all of humanity. I doubt anyone would disagree with that.
Michael:
In what way can the rocket exert gravity on the asteroid? It is probably thousands of times smaller than him(?)
And what is the factor that will change the distinction in an asteroid, between days and years?
And a third question: If a "barrage" of comets moves in our direction, is the probability that they will hit two planets, for example both Earth and Mars, high?
It turns out that the Hugins don't die but just change names
So you got it white blood?
Apparently Hiroshima, Nagasaki and the Jewish and Gypsy people were also types of disturbing bodies on the ground 70 years ago and in the degree of "crispness" corresponding to the performance of the act proposed by the on-duty explainer or the tasteless and odorless imitator who replied
Go in comment 6 and.. popss.. fade away. popsss..
Ha..haha nonsense in tomato juice.Gournish!Doesn't count.
They didn't mean to, it was just self-defense. Advance preparation, planning...
So you got the idea, white blood? Red blood, blue blood, purple blood.. what does it matter anymore.
white blood:
All kinds of alternatives are being examined, which include crushing the asteroid with atomic bombs and deviating it from its orbit in various ways, including, among other things, pushing it using engines and gravitational drag by a missile that will cruise near it and exert a (minor) gravitational force on it for a long time.
What is the preferred method is difficult to know when there is no information about the structure of the asteroid (and especially about its brittleness) and the success of the defensive operation depends to a large extent on the time of its discovery.
If you discover it years before - it is quite certain that you can be saved.
If it is discovered the day before the injury - there is almost no chance.
White blood, it is unpleasant to admit a mistake, but questions like these you should direct to the Russians, they are experts in telekinesis :)
I was always scared by the idea of a comet colliding with the Earth.
In your opinion, if a situation occurs where an asteroid/comet moves in our direction, we will have enough time to prepare for it and act accordingly? And if so, what can be done about it? Will it be possible to destroy it or divert it from its course?
Agnus:
None of the conclusions could be reached based on the statistics you offer (and therefore they were not reached before running the model).
If you think otherwise, you are welcome to write an article describing an orderly logical process in which you draw the conclusions drawn by the research from the data you offered.
This article will be accepted without any problem in any respected scientific journal such as Nature or Science
The model includes the evolution of the Oort and from it predicts the amount of comets. We don't know how many comets were in our area in the past.
I did not understand what was the advantage of the computerized model that could not be done with a simple statistical calculation of the amount of asteroids observed by us to date.
We should also mention the comet Shoemaker-Levy that crashed into Jupiter and received tremendous ratings.