Listen to CheapGPT talk about wandering balloons

After learning general physics in college, it is easy to speculate and answer some questions that everyone is concerned about from the few words in the news. For example, what is the structure of this balloon? Why can it go up and down? How to control it and why does it lose control? How heavy is it? How much is it worth? In order to shoot it down, the US military F22, tanker and missiles are used together. Is this just a show of skill? Is there any simple way to shoot down a balloon?

Written by Ji Yang (Researcher at the Institute of Semiconductors, Chinese Academy of Sciences)

There are two hot topics these days: one is that the American company OpenAI developed the chatbot ChatGPT, and the other is that the United States used aircraft and missiles to shoot down China's out-of-control civilian balloons.

Because it involves both China and the United States, these two topics are very hot, but I haven't seen anyone using ChatGPT to seriously discuss stray balloons. According to Lubianshe's analysis, the reason is this: it is unethical to write articles using ChatGPT, and jumping the wall is not in line with public order and good customs; in addition, ChatGPT is a people-pleasing personality (Editor's note: See "Scientific Journals Ban ChatGPT from Being Listed as an Author of Papers, What Does ChatGPT Think?"), and he doesn't know what will happen after 2022. So, if you talk to him about stray balloons, you can only talk nonsense.

In the era of artificial intelligence, we must be innovative to ensure that our jobs are not taken away by AI. So let's use ChatGPT to talk about wandering balloons.

The basic idea is this. There is a saying in the United States: Chat is cheap, show me the balloon. This is foreign language, you don’t understand, let me explain: ChatGPT is CheapGPT, so let’s talk about balloons.

The full name of ChatGPT is Chat Generative Pre-trained Transformer, and the full name of CheapGPT is Cheap Gerneral Physics Teacher.

Without further ado, let's get down to business. As a CheapGPT, it's easy for me to speculate and answer some of the questions that everyone is concerned about from the few words in the news. For example, what is the structure of this balloon? Why can it go up and down? How to control it and why does it lose control? How heavy is it? How much is it worth? In order to shoot it down, the US military used F22, tankers and missiles together. Is this just a show of skill? Is there any simple way to shoot down a balloon?

The only information we can see is "the US claims that the balloon is about 60 meters (200 feet) high and has a long sensor underneath", and that the balloon can float to an altitude of 30,000 to 40,000 meters (so the US military could only stare blankly at first, and only started to show off their power when the balloon dropped to an altitude of 20,000 meters). Let's analyze it based on this information.

This balloon can float high in the sky, and the gas inside must be lighter than air. Heating is not realistic (because it needs to float for a long time), the density of methane is too small to be different from that of air, and hydrogen is easy to explode, so it can only be helium.

The amount of helium required should be divided by a factor of about 50. Therefore, it would cost about 300,000 or 400,000 yuan to fill such a large balloon with helium, which is not that outrageous. Of course, 400,000 yuan is not a small amount of money. This balloon is definitely not a cheap one sold for a few hundred or a few thousand yuan on Taobao. At the same time, we have also proved that the phrase "Chat is cheap, show me the balloon" is completely equivalent to the more common "Chat is cheap, show me the money".

This balloon can go up and down, can bend and stretch, because its volume can change at will, otherwise Comrade Archimedes would not be so easy to talk to. The specific control method should be: put a small balloon inside the big balloon, and the pressure in the two balloons is different. Pump some air from the big balloon into the small balloon, the pressure in the big balloon will be lower than the air pressure outside, the big balloon will be flattened a little, and the buoyancy will be insufficient, so the balloon will fall to a new equilibrium height. It is easy to pump air, but it is necessary to ensure that the air extraction pipeline and the connection part of the two balloons and the valve are well sealed (because helium is very expensive and is a non-renewable resource.), as well as the automatic control of the air pump, which should reflect the technical ability. There is news that the balloon has three layers. I guess it is for easier control (there may also be material considerations), or the protective net outside the big balloon is also counted as a layer (the protective net is to share the load of the balloon. If only one rope is used, it will strangle our balloon).

We can also estimate the size of the small balloon. The total weight of the balloon is constant (as we just calculated, it weighs about 10,000 cubic meters of air, which is about 10 tons). Since the balloon was once docked on the ground, the buoyancy of the small balloon itself is roughly the same level. Therefore, the size of the small balloon is about one-fifth of the large balloon, which is about 15 meters in diameter.

Let's estimate the thickness of the balloon skin. The surface area of ​​a large balloon is about 10,000 square meters, and the weight is 2 tons, so each square meter weighs about half a pound. The density of the balloon skin is not much different from that of water, so it cannot be more than 1 cm thick. Considering that we have three layers of skin, nitrogen, and payload, it is safe to guess that the thickness of this balloon skin should be less than 1 mm, and should be between 0.2 mm and 2 mm.

The thing under the balloon that is several dozen meters long is mainly a solar panel. This thing should not be very expensive, and the observation instrument should not be particularly valuable either, because the balloon is very close to the ground and moves very slowly, so it does not need the high-end optical lenses on satellites. The data should be directly transmitted to communication satellites or ground base stations, and these things are not valuable either. Someone posted an announcement from a certain scientific institute on the Internet, which clearly stated that the winning bid amount was 3.16 million. Although there are no details, it should be reliable: because this is research and development, not mass production. According to our analysis here, the cost alone should be one or two million.

Among the bits and pieces hanging under the balloon, there should be some big fans to help the balloon run. Just blow the wind behind it and it can run forward: why is it said that "if you go east, the western barbarians will complain, and if you go south, the northern barbarians will complain"? It's because this pillow wind is too terrible. Of course, because the balloon is too big and it runs too fast, its athletic ability is very average, and our control over it is also very limited. If we are unlucky and encounter a strong wind in the sky, we will become a wandering balloon. If we are unlucky enough to be shot down, our balloon can only "go away and never return."

Well, that's all about the properties of balloons. Now let's talk about how they were discovered, how they were shot down, and why it is so difficult to shoot down balloons from a purely technological perspective.

First of all, although the balloon is big, it doesn't have much material except for being full of gas. Therefore, it is not easy for radars and satellites to see it, because it has a weak reflection of radio waves and the satellite is too far from the ground. But, but, the human eye can see it. There is a big balloon with a diameter of 60 meters floating 30 kilometers above your head. The visual angle is about 2 milliradians, which is only slightly smaller than the sun and the moon (their visual angles are about 10 milliradians). It can be said to be the third largest object in the sky. Especially in the morning, the huge balloon reflects the morning sun, which is really like a shining red star. It is hard not to see it. No wonder Hollywood released a movie two years ago to call on everyone not to look up, because you can see it as soon as you look up.

Why is it so hard to hit a balloon? Why do we have to use F22, tankers and missiles? Because the air above 20,000 meters is very thin, and airplanes cannot fly. In addition, airplanes usually launch missiles forward and downward. Your balloon is now in the sky, and my airplane can only point its head upward, which is not easy to use. As the saying goes, "A swan flies high and can fly thousands of miles in one go. Even if you have a bow and arrow, what can you do with it?" If the foreign devils don't understand this sentence, let them ask ChatGPT themselves.

You may ask, isn't it enough to let a drone with a Browning rush over and shoot him a few times? What's the big deal? First of all, drones can't fly that high. In addition, even if the bullets make a few holes, the air will leak out too slowly: if the hole is 1 cm, the air in the balloon will not be completely leaked out in a day or two - a very simple arithmetic problem, leave it to ChatGPT to do. In addition, if your plane flies too close, it's okay if the balloon doesn't explode. If it really explodes, the fragments can easily be rolled into the plane engine. At that time, it is unclear whether it was the plane that hit the balloon or the balloon that hit the plane.

Recently, there is news that an unidentified flying object was found in the sea near Rizhao, Shandong, and the relevant departments are preparing to shoot it down. Well, if this is true, how can we shoot down the balloon? Of course, we can shoot it down with a missile, but this method is quite expensive; we can also poke it down with a bamboo pole, but this is a unique skill and will not be used easily until the critical moment.

I think the best way is to use a laser cannon, preferably an airborne one. Just send a plane over there, it doesn't need to fly very high, just go above the clouds, 10,000 meters is definitely enough. We just calculated that for a 60-meter balloon, at a distance of 30 kilometers, the viewing angle is 2 milliradians, which means a coin is placed at a distance of 5 meters. You don't even need Xu Haifeng, I can do it too. A 20-centimeter-diameter telescope and a 1-kilowatt laser (pulsed ones are better) can focus the light beam on the balloon to a size of 40 centimeters (this involves the relationship between the diffraction limit and the aperture of optical instruments, both of which are basic contents of optics in university physics). It will definitely make a big hole with one hit! As the saying goes, "In the midst of talking and laughing, masts and oars are reduced to ashes!"

Dear viewers and listeners, good morning, good afternoon, good evening. I have finished my story. Please tell me how this story went. If you know how to play ChatGPT, please go and try it out.

Tsk, what is ChatGPT? Is it really comparable to our CheapGPT?

This article is supported by the Science Popularization China Starry Sky Project

Produced by: China Association for Science and Technology Department of Science Popularization

Producer: China Science and Technology Press Co., Ltd., Beijing Zhongke Xinghe Culture Media Co., Ltd.

Produced by: Science Popularization China

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