the picture you show, has 4 objects, two at low redshift, two at higher redshift. The two low redshifts are pretty close. (difference is.027) which may be explainable by local motions. The two high redshift objects can just be background galaxies. This doesn't falsify the conventional expanding universe model.
For this to mean anything data from one of the survey instruments needs to be analyzed to see if overlaps like this happen more often than would be expected randomly (including lensing). Its not a difficult analysis, but someone has to take the time to do it. There is some data in public domain. An interested person an analyze and publish.
Yes, big bang can and in its original form has been falsified. The original version was just free expansion in the presence of matter and electromagnetic radiation. Measurements disagreed with that model at fit better a model where there was additional invisible matter (with some constraints on rest mass), and a "inflation" field which went away early in the universe's history Later measurements showed that there was also an "dark energy" field that is similar to the inflation field, but at a very much lower energy density.
So yes, the original model did fail, and new models were developed.
What is still quite solid is that at some point roughly 14 billion years ago, all matter was in a compact volume at high pressure and temperature. How it "got there" (if that question is even well defined, and details of the physics of the early universe are still under investigation.
For the books: just the amazon summary says that quasars are local objects. That contradicts observations of gravitational lensing of quasars by galaxies. Decades ago there was debate over whether quasars were local or not, but that has been settled. Since the book seems to be proposing a theory that disagrees with a large number of measurements, I don't see any point in reading the rest.
I think part of the problem is that people outside of the field don't realize the incredible wealth of data we now have on cosmology. This is very different from the case 50 years ago when there was very limited data and a lot of room for a wide range of theories.
Jansky was creating a new field - he was using a new technology (radio) to perform new measurements. That is very different from having new "ideas" without any new data in a well established field. In order to have new idea, you need to understand the field as it exists, or you won't know what measurements have already been done.
There may be very interesting new astrophysics data if, for example, someone finds a way to efficiently detect dark matter. (there are some ideas based on quantum entanglement, but so far they aren't very practical). Gravity waves have opened up a new window - but the detectors are extremely expensive and are the result of decades of work in the field. Advances in computation are making large scale synthetic aperture telescopes practical - and there are several projects planning to implement this.
If someone finds a new type of measurement to do for astrophysics / cosmology, there will be a LOT of interest.
I wish the idea of Einstein as an outsider had not somehow invaded popular thinking. He was a brilliant guy, and he came up with a new way to describe a set of existing observations and which also made predictions that were soon verified. He had a physics degree, just like many he had difficulty finding a teaching position. He was recognized soon after publishing a paper on special relativity.
videos are a really inconvenient way to present technical information. Are there papers?
Very careful statistics are needed to look for correlations between high and low redshift objects. Its easy for a survey to be biased by brighter objects being counted at the same redshift were dimmer objects are missed. Then gravitational lensing will provide real correlations that need to be subtracted out.
Gravitational lensing of distant quasars by closer galaxies, and of the CMB background by closer objects (from statistical surveys) is very strong evidence that redshift is distance correlated. This is separate from and supports data from supernova. Things like the LIGO in-spiral measurement add yet more independent confirmation.
Its difficult to imagine a model that fits the huge amount of existing data that doesn't have redshifts correlated with distance. If someone has such a model, they have to show that it is consistent with ALL the known data - and *they* have to do the legwork to show that. Its so unlikely that working scientists are not going to be able to get funding to study it. Funding is very limited so it gets spent in directions that are most likely to produce results. (how else would you decide where to spend it).
Dark energy was a very important and unexpected discovery - but I don't think it was one that could have been predicted until acceleration started to show up in high precision data. Einstein's equations included a term that could cause acceleration, but there was no reason to think it was non-zero in the modern universe until there was data.
Neutrino oscillations were an important discovery, but again no particular reason to expect them without data.
What major paradigm shifts are you thinking of in the last 50 years in well established fields and which of those came from outside of the established scientific community? In new fields, there is a lot of opportunity for new ideas. In old fields it can happen, but the invention of relativity is a pretty typical example: a brilliant person from *inside* of the scientific community finds a different way describe existing data, and makes new testable predictions.
Science is a very complex web of interacting theories and experiments. Any new theory has to not only explain a particular phenomena, but to not contradict a great many other experiments. This rules out a great many alternate theories. This isn't taking "sides", it is just trying to find theories that are consistent with experiments.
There is some "bias" against non-scientists, but that is because people outside of the field are unlikely to know all of the measurements that have been done. Scientists don't have infinite time, so they are not likely to be willing to do the leg-work of doing research for people who haven't already done a lot of that work themselves.
It is pretty rare for someone outside of a well established field to make a major contribution.
Scientists do try to find entirely new theories. I was at conference where one of the speakers mentioned how many theories had died the day that LIGO saw gravity waves from the neutron star collision - the measurement that gravity waves traveled at the same speed as electromagnetic radiation to very high precision, ruled out a range of alternative gravity theories.
In this case though, there are lots of effects that depend on the strength of magnetic fields in galaxies so they can't be very far from what is predicted by conventional astrophysics.
I think its more expensive than it is hard. I expect most of the standard fusion devices would work if scaled up - the trick is finding one that can be made at a reasonable size (with ITER maybe not qualifying as "reasonable").
Fusion isn't really mysterious. You need to keep the plasma above some temperature at a sufficiently high product of pressure and lifetime. This improves as the machine gets larger.
Different field configurations (tokomak, stellerator etc) can provide different scaling of storage time relative to size. At the time ITER was designed, Tokomak looked the best. I don't know if any new information has changed that.
ITER has been slow / expensive because it is a giant multi-national collaboration, IMHO the least efficient way to do a project. I bet Apple could have built the same thing for the cost of their ridiculous new headquarters.
People are looking at a lot of more exotic ideas, like the colliding ring machine (tri-alpha) with a general goal of increasing the ion temperature (needed for fusion) relative to the electron temperature (just causes energy loss) but so far they haven't looked that promissing.
Most of the standard plasma fusion machines can work if scaled to large enough sizes. Do stellerators scale better than tokomaks? Its a detailed technical question that probably depends on a variety of design constraints.
I assume ITER went with a Tokomak because it scaled to smaller sizes than any of the other configurations based on the technological constraints at the time. If the technology has changed, maybe there is a better optimum, but I haven't seen a good technical comparison .
What is the issue. (not disagreeing, I just don't know much about high field magnets). I assume all the fusion machines already use the strongest available magnets - is this group claiming a new significant magnet technology advance that post-dates the ITER design? Is it not practical for some reason?
Corporate culture varies a lot between companies. Harassment is very bad some places, almost non-existant in others. If it was low at your companies, then that is great, you were part of a culture that didn't allow it. That doesn't mean that it doesn't exist at other companies.
Assuming the article accurately represents how she was treated, this is completely absolutely off the curve not OK. I don't know how common this is, but there are enough reports from enough different people at different companies that I believe its pretty widespread.
I've found that workplaces that have a larger percentage of older workers tend to do a lot better. Maybe the older workers who act like adults at work serve as role models for younger workers. In my (second hand) experience even the defense industry is far better than high-tech.
I would not tolerate anything like this sort of behavior in my group. I'm paying people (generally quite well) to do really interesting, really difficult work. I need all of them, and the last thing I want is some immature idiot making it more difficult for someone else in my group to do their work.
Whenever someone wants to add something new to the school curriculum, they need to say what topics should be dropped to replace it. That might be fine- I expect many schools still teach cursive writing for example, but the tradeoff needs to be made
Personally I'd put economics ahead of computer science on things to be added to schools.
I'm happy to pay for content IF there is an easy, safe, reasonably anonymous way to do it. A micro-payment system would solve all of this. The problem is that the way things are now, there is no low-risk way for me to send a few cents to the owner of a page.
I use an ad-blocker because on some pages the ads are so intrusive that I can't read the content. I fell OK about it because the ads are so badly targeted that I can't remember EVER intentionally clicking on an ad. (ads that slide under your mouse so you accidentally click on them don't count). If I were shown ads for things I'm interested in, I'd be happy to look at them.
If the system is secure, I have no problem with mining as a way to collect micro-payments (other than the overall environmental disaster that is crypto-currency)
When cars and aircraft were first invented, someone with modest mechanical talent could modify or even build one in their garage. Now they are so sophisticated that its very difficult for a non-expert to make any useful improvements.
Going back further, when people used dug-out canoes and rafts, a little training would let someone build a boat. Later it became a job for experts.
This may just be what is expected for a mature engineering field.
BTW - people *can* do home-made modified cars, planes and boats, but its generally at a hobby level and the skills are not that closely related to what is needed for commercial systems. This is similar to learning program rasberry pi, or similar.
A site that allowed you to view their content with the agreement that you let them mine on your computer while you are doing so might not be a terrible way to go.
I agree that a significant part of this is a physics problem. It would be possible to test whether or not this is algorithmic by training a recognizer on a high percentage of dark skinned people and seeing what its performance was like on light skinned people.
A lot of modern cameras / cell phones have live face detection features. A photo setting that set exposure for faces would help this. People might not use it much though - if you have a dark skinned person in a scene, many people may still prefer the face to be under-exposed rather than the rest of the scene partially saturated.
It would be possible to test whether or not this is algorithmic by training a recognizer on a high percentage of dark skinned people and seeing what its performance was like on light skinned people.
They might want to destroy any technological civilization before it becomes a threat.
They might have something resembling religious reasons. (which seem to cause humans to engage in vast senseless projects - pyramids and sending missionaries to low-tech cultures in the Amazon) .
Maybe they find a race of predators like humans as horrifying as we would find a race of parasitic wasps.
Who knows what resources they need? 100,000 years ago humans lived near watering holes. They would have no idea why we value and fight over random bits of desert that don't have good water or game.
But yes - they are likely vastly superior in technology, so if does happen, they will win - which is why it is a threat.
You would have to look at the distribution of dust sizes in the interstellar medium. Gram sized objects may be quite rare.
A gram at 0.1C would be 10 tons of explosives which sounds bad - but maybe not so bad. If you use a fission rocket, you can build the structure of the rocket out of fuel and add a large shield. Imagine using Throium - you could have a large thick throium shield which you slowly consume to breed into fissionable material, then use in your reactor. Since you need fuel to decelerate you are slow by the time the fuel is gone.
These are probably slow acceleration rockets (0.001G or so) due to power dissipation limits. So a gossamer structure to support a think shield a kilometer ahead of the ship might not be too heavy. Occasionally it would get destroyed by a small rock - but the rock would evaporate and cause less damage to the ship. Then you rebuild the outer shield.
I do agree that there is no way to do this with human societies as they exist now. No easy way to know if alien intelligence would be anything similar. Maybe they are happy to spend 100 generations doing nothing but sitting and eating. (like cats....).
The expense is a real issue - but also difficult to scale. Can this be built by self-exponentiating automation? Or maybe there is some other drive - seems like something a planetary scale civilization could do in not many years. Maybe they have a drive to expand. Even with a doubling time of 10,000 years, it doesn't take long to colonize the galaxy.
I just don't know how to guess at motivations. Try explaining to a paleolithic human why you are posting on slashdot - and that's the same species.
I think you've dropped a few digits. Crossing the galaxy at light speed would take 100K years. but the universe is >10Billion years old, so you could do it 100 thousand times before the universe doubled in age. It only seems long on human time scales.
A slow ageing race could easily colonize a galaxy, maybe a local cluster
Europe colonized much of the world in 500 years. At that tech level, a round-the-world trip took on the order of a year, so 500 round trips. Even at 0.1C, a galaxy round trip is 2 million years. - to in a billion years (10% of the universe age) you could similarly colonize the galaxy.
I do have a rather good idea of how distant stars are, and of how improbable faster than light travel is - but you are taking a limited view of technology.
With technology we understand now you can get to about 0.1C, in maybe 100 years. (that is a power density that you can radiate with reasonable radiators, and energy densities compatible with fission reactors). So we are talking a few thousand year trips.
But is that so bad? Even humans have worked on single projects that lasted 100 years (like the NY 2nd avenue subway). Is a few thousand so out of line? Maybe they are longer lived that we are.
Maybe they have already exponentiated into most solar systems and are waiting. (robots, hibernation whatever). They could be "predators" who destroy any technological civilizations before they become an interstellar threat.
Maybe they do it for religious reasons. Or for something as incomprehensible to us as religion is to a cat. Maybe invasion is the wrong word, and they just want to build a hyperspace bypass (just kidding).
Likely - no. But I don't see how you can rule it out. Interstellar travel at a fraction of C is really not that difficult with technology we already understand (but of course don't yet have). Near C may be possible and we just don't know how yet. (making antimatter seems difficult but maybe there is a trick).
Why is it stupid? There are a lot of habitable planets. We have absolutely no idea of the probabilities of them developing life, developing intelligence, developing technology, deciding to invade. But if they do , we lose. (the guys on the ships win).
Its not likely but similar to asteroid impacts, its statistically probably more likely to kill you than terrorists are.
I would expect an authoritarian government to use all the tools at its disposal to run the country efficiently. Its not something I want to see happen in the US, but seems in line with Chinese policies and not particularly evil.
Slashdot Mirror
I don't see the falsifying data.
the picture you show, has 4 objects, two at low redshift, two at higher redshift. The two low redshifts are pretty close. (difference is .027) which may be explainable by local motions. The two high redshift objects can just be background galaxies. This doesn't falsify the conventional expanding universe model.
For this to mean anything data from one of the survey instruments needs to be analyzed to see if overlaps like this happen more often than would be expected randomly (including lensing). Its not a difficult analysis, but someone has to take the time to do it. There is some data in public domain. An interested person an analyze and publish.
Yes, big bang can and in its original form has been falsified. The original version was just free expansion in the presence of matter and electromagnetic radiation. Measurements disagreed with that model at fit better a model where there was additional invisible matter (with some constraints on rest mass), and a "inflation" field which went away early in the universe's history Later measurements showed that there was also an "dark energy" field that is similar to the inflation field, but at a very much lower energy density.
So yes, the original model did fail, and new models were developed.
What is still quite solid is that at some point roughly 14 billion years ago, all matter was in a compact volume at high pressure and temperature. How it "got there" (if that question is even well defined, and details of the physics of the early universe are still under investigation.
For the books: just the amazon summary says that quasars are local objects. That contradicts observations of gravitational lensing of quasars by galaxies. Decades ago there was debate over whether quasars were local or not, but that has been settled. Since the book seems to be proposing a theory that disagrees with a large number of measurements, I don't see any point in reading the rest.
I think part of the problem is that people outside of the field don't realize the incredible wealth of data we now have on cosmology. This is very different from the case 50 years ago when there was very limited data and a lot of room for a wide range of theories.
Jansky was creating a new field - he was using a new technology (radio) to perform new measurements. That is very different from having new "ideas" without any new data in a well established field. In order to have new idea, you need to understand the field as it exists, or you won't know what measurements have already been done.
There may be very interesting new astrophysics data if, for example, someone finds a way to efficiently detect dark matter. (there are some ideas based on quantum entanglement, but so far they aren't very practical). Gravity waves have opened up a new window - but the detectors are extremely expensive and are the result of decades of work in the field. Advances in computation are making large scale synthetic aperture telescopes practical - and there are several projects planning to implement this.
If someone finds a new type of measurement to do for astrophysics / cosmology, there will be a LOT of interest.
I wish the idea of Einstein as an outsider had not somehow invaded popular thinking. He was a brilliant guy, and he came up with a new way to describe a set of existing observations and which also made predictions that were soon verified. He had a physics degree, just like many he had difficulty finding a teaching position. He was recognized soon after publishing a paper on special relativity.
videos are a really inconvenient way to present technical information. Are there papers?
Very careful statistics are needed to look for correlations between high and low redshift objects. Its easy for a survey to be biased by brighter objects being counted at the same redshift were dimmer objects are missed. Then gravitational lensing will provide real correlations that need to be subtracted out.
Gravitational lensing of distant quasars by closer galaxies, and of the CMB background by closer objects (from statistical surveys) is very strong evidence that redshift is distance correlated. This is separate from and supports data from supernova. Things like the LIGO in-spiral measurement add yet more independent confirmation.
Its difficult to imagine a model that fits the huge amount of existing data that doesn't have redshifts correlated with distance. If someone has such a model, they have to show that it is consistent with ALL the known data - and *they* have to do the legwork to show that. Its so unlikely that working scientists are not going to be able to get funding to study it. Funding is very limited so it gets spent in directions that are most likely to produce results. (how else would you decide where to spend it).
Which discoveries are you thinking of?
Dark energy was a very important and unexpected discovery - but I don't think it was one that could have been predicted until acceleration started to show up in high precision data. Einstein's equations included a term that could cause acceleration, but there was no reason to think it was non-zero in the modern universe until there was data.
Neutrino oscillations were an important discovery, but again no particular reason to expect them without data.
What major paradigm shifts are you thinking of in the last 50 years in well established fields and which of those came from outside of the established scientific community? In new fields, there is a lot of opportunity for new ideas. In old fields it can happen, but the invention of relativity is a pretty typical example: a brilliant person from *inside* of the scientific community finds a different way describe existing data, and makes new testable predictions.
Science is a very complex web of interacting theories and experiments. Any new theory has to not only explain a particular phenomena, but to not contradict a great many other experiments. This rules out a great many alternate theories. This isn't taking "sides", it is just trying to find theories that are consistent with experiments.
There is some "bias" against non-scientists, but that is because people outside of the field are unlikely to know all of the measurements that have been done. Scientists don't have infinite time, so they are not likely to be willing to do the leg-work of doing research for people who haven't already done a lot of that work themselves.
It is pretty rare for someone outside of a well established field to make a major contribution.
Scientists do try to find entirely new theories. I was at conference where one of the speakers mentioned how many theories had died the day that LIGO saw gravity waves from the neutron star collision - the measurement that gravity waves traveled at the same speed as electromagnetic radiation to very high precision, ruled out a range of alternative gravity theories.
In this case though, there are lots of effects that depend on the strength of magnetic fields in galaxies so they can't be very far from what is predicted by conventional astrophysics.
I think its more expensive than it is hard. I expect most of the standard fusion devices would work if scaled up - the trick is finding one that can be made at a reasonable size (with ITER maybe not qualifying as "reasonable").
Fusion isn't really mysterious. You need to keep the plasma above some temperature at a sufficiently high product of pressure and lifetime. This improves as the machine gets larger.
Different field configurations (tokomak, stellerator etc) can provide different scaling of storage time relative to size. At the time ITER was designed, Tokomak looked the best. I don't know if any new information has changed that.
ITER has been slow / expensive because it is a giant multi-national collaboration, IMHO the least efficient way to do a project. I bet Apple could have built the same thing for the cost of their ridiculous new headquarters.
People are looking at a lot of more exotic ideas, like the colliding ring machine (tri-alpha) with a general goal of increasing the ion temperature (needed for fusion) relative to the electron temperature (just causes energy loss) but so far they haven't looked that promissing.
Most of the standard plasma fusion machines can work if scaled to large enough sizes. Do stellerators scale better than tokomaks? Its a detailed technical question that probably depends on a variety of design constraints.
I assume ITER went with a Tokomak because it scaled to smaller sizes than any of the other configurations based on the technological constraints at the time. If the technology has changed, maybe there is a better optimum, but I haven't seen a good technical comparison .
What is the issue. (not disagreeing, I just don't know much about high field magnets). I assume all the fusion machines already use the strongest available magnets - is this group claiming a new significant magnet technology advance that post-dates the ITER design? Is it not practical for some reason?
If they can use higher magnetic fields, that increases the pressure and decreases required volume of the reactor to get to breakeven.
That said, the picture the show looks really small even with high field magnets .
We'll see. There have been a lot of claims of practical fusion in the next few years. So far non have worked, but its not fundamentally impossible.
Corporate culture varies a lot between companies. Harassment is very bad some places, almost non-existant in others. If it was low at your companies, then that is great, you were part of a culture that didn't allow it. That doesn't mean that it doesn't exist at other companies.
Assuming the article accurately represents how she was treated, this is completely absolutely off the curve not OK. I don't know how common this is, but there are enough reports from enough different people at different companies that I believe its pretty widespread.
I've found that workplaces that have a larger percentage of older workers tend to do a lot better. Maybe the older workers who act like adults at work serve as role models for younger workers. In my (second hand) experience even the defense industry is far better than high-tech.
I would not tolerate anything like this sort of behavior in my group. I'm paying people (generally quite well) to do really interesting, really difficult work. I need all of them, and the last thing I want is some immature idiot making it more difficult for someone else in my group to do their work.
Whenever someone wants to add something new to the school curriculum, they need to say what topics should be dropped to replace it. That might be fine- I expect many schools still teach cursive writing for example, but the tradeoff needs to be made
Personally I'd put economics ahead of computer science on things to be added to schools.
I'm happy to pay for content IF there is an easy, safe, reasonably anonymous way to do it. A micro-payment system would solve all of this. The problem is that the way things are now, there is no low-risk way for me to send a few cents to the owner of a page.
I use an ad-blocker because on some pages the ads are so intrusive that I can't read the content. I fell OK about it because the ads are so badly targeted that I can't remember EVER intentionally clicking on an ad. (ads that slide under your mouse so you accidentally click on them don't count). If I were shown ads for things I'm interested in, I'd be happy to look at them.
If the system is secure, I have no problem with mining as a way to collect micro-payments (other than the overall environmental disaster that is crypto-currency)
When cars and aircraft were first invented, someone with modest mechanical talent could modify or even build one in their garage. Now they are so sophisticated that its very difficult for a non-expert to make any useful improvements.
Going back further, when people used dug-out canoes and rafts, a little training would let someone build a boat. Later it became a job for experts.
This may just be what is expected for a mature engineering field.
BTW - people *can* do home-made modified cars, planes and boats, but its generally at a hobby level and the skills are not that closely related to what is needed for commercial systems. This is similar to learning program rasberry pi, or similar.
A site that allowed you to view their content with the agreement that you let them mine on your computer while you are doing so might not be a terrible way to go.
I agree that a significant part of this is a physics problem. It would be possible to test whether or not this is algorithmic by training a recognizer on a high percentage of dark skinned people and seeing what its performance was like on light skinned people.
A lot of modern cameras / cell phones have live face detection features. A photo setting that set exposure for faces would help this. People might not use it much though - if you have a dark skinned person in a scene, many people may still prefer the face to be under-exposed rather than the rest of the scene partially saturated.
It would be possible to test whether or not this is algorithmic by training a recognizer on a high percentage of dark skinned people and seeing what its performance was like on light skinned people.
Lots of possible reasons:
They might want to destroy any technological civilization before it becomes a threat.
They might have something resembling religious reasons. (which seem to cause humans to engage in vast senseless projects - pyramids and sending missionaries to low-tech cultures in the Amazon) .
Maybe they find a race of predators like humans as horrifying as we would find a race of parasitic wasps.
Who knows what resources they need? 100,000 years ago humans lived near watering holes. They would have no idea why we value and fight over random bits of desert that don't have good water or game.
But yes - they are likely vastly superior in technology, so if does happen, they will win - which is why it is a threat.
You would have to look at the distribution of dust sizes in the interstellar medium. Gram sized objects may be quite rare.
A gram at 0.1C would be 10 tons of explosives which sounds bad - but maybe not so bad. If you use a fission rocket, you can build the structure of the rocket out of fuel and add a large shield. Imagine using Throium - you could have a large thick throium shield which you slowly consume to breed into fissionable material, then use in your reactor. Since you need fuel to decelerate you are slow by the time the fuel is gone.
These are probably slow acceleration rockets (0.001G or so) due to power dissipation limits. So a gossamer structure to support a think shield a kilometer ahead of the ship might not be too heavy. Occasionally it would get destroyed by a small rock - but the rock would evaporate and cause less damage to the ship. Then you rebuild the outer shield.
I do agree that there is no way to do this with human societies as they exist now. No easy way to know if alien intelligence would be anything similar. Maybe they are happy to spend 100 generations doing nothing but sitting and eating. (like cats....).
The expense is a real issue - but also difficult to scale. Can this be built by self-exponentiating automation? Or maybe there is some other drive - seems like something a planetary scale civilization could do in not many years. Maybe they have a drive to expand. Even with a doubling time of 10,000 years, it doesn't take long to colonize the galaxy.
I just don't know how to guess at motivations. Try explaining to a paleolithic human why you are posting on slashdot - and that's the same species.
I think you've dropped a few digits. Crossing the galaxy at light speed would take 100K years. but the universe is >10Billion years old, so you could do it 100 thousand times before the universe doubled in age. It only seems long on human time scales.
A slow ageing race could easily colonize a galaxy, maybe a local cluster
Europe colonized much of the world in 500 years. At that tech level, a round-the-world trip took on the order of a year, so 500 round trips. Even at 0.1C, a galaxy round trip is 2 million years. - to in a billion years (10% of the universe age) you could similarly colonize the galaxy.
I do have a rather good idea of how distant stars are, and of how improbable faster than light travel is - but you are taking a limited view of technology.
With technology we understand now you can get to about 0.1C, in maybe 100 years. (that is a power density that you can radiate with reasonable radiators, and energy densities compatible with fission reactors). So we are talking a few thousand year trips.
But is that so bad? Even humans have worked on single projects that lasted 100 years (like the NY 2nd avenue subway). Is a few thousand so out of line? Maybe they are longer lived that we are.
Maybe they have already exponentiated into most solar systems and are waiting. (robots, hibernation whatever). They could be "predators" who destroy any technological civilizations before they become an interstellar threat.
Maybe they do it for religious reasons. Or for something as incomprehensible to us as religion is to a cat. Maybe invasion is the wrong word, and they just want to build a hyperspace bypass (just kidding).
Likely - no. But I don't see how you can rule it out. Interstellar travel at a fraction of C is really not that difficult with technology we already understand (but of course don't yet have). Near C may be possible and we just don't know how yet. (making antimatter seems difficult but maybe there is a trick).
Why is it stupid? There are a lot of habitable planets. We have absolutely no idea of the probabilities of them developing life, developing intelligence, developing technology, deciding to invade. But if they do , we lose. (the guys on the ships win).
Its not likely but similar to asteroid impacts, its statistically probably more likely to kill you than terrorists are.
I would expect an authoritarian government to use all the tools at its disposal to run the country efficiently. Its not something I want to see happen in the US, but seems in line with Chinese policies and not particularly evil.