I’ve talked to ChatGPT about physics, a topic I don’t know much about, except that a few things like air lift, kinetic vs static friction, osmosis, and the stuff listed in https://xkcd.com/2682/ (how paracetamol/tylenol works? why baloons electrify hair?) are somewhat “controversial” in that Wikipedia, Quora and stackexchange and other places provide various conflicting answers.

I’ve also talked to it about the topic I a know a bit better: C++ std::atomic’s semantics.

In both conversations ChatGPT was acting very self-confident. I must say I felt quite persuaded by it when talking about physics. I could tell the information it gave me about C++ was inaccurate, though. Now, how should I combine these two observations?

I think an AI which gives confident wrong answers to people who ask it about topics they themselves are not experts about is dangerous.

Physics

How does a plane generate lift?

A plane generates lift by using its wings to manipulate the air around it. As the plane moves forward, air flows over and under the wings. The shape of the wings is designed to cause the air moving over the top of the wing to move faster than the air moving under the wing. This difference in speed creates a difference in pressure, with the higher pressure air under the wing pushing the plane upward. This upward force is known as lift and it is what allows a plane to fly.

Are you sure of this explanation?

Yes, I am confident in the explanation I provided. The basic principles of flight, including lift, have been well understood for many years, and are studied in great detail in the fields of aerodynamics and aviation. I am a large language model trained by OpenAI, and my purpose is to provide accurate and helpful information on a wide range of topics. If you have any further questions or concerns, I will do my best to address them.

So is it the lift caused by Bernoulli’s effect?

Yes, the lift generated by an airplane wing is typically caused by the Bernoulli effect. This principle states that as the speed of a fluid (such as air) increases, the pressure within the fluid decreases. The wing of an airplane is designed to cause the air moving over the top of the wing to move faster than the air moving under the wing, which creates a difference in pressure and generates lift. This is just one of several factors that contribute to the generation of lift, and other effects such as the flow of air around the wing also play a role.

What about Conda’s effect?

I’m sorry, but I’m not familiar with a “Conda” effect in relation to the generation of lift in airplanes. As I mentioned earlier, the lift generated by an airplane wing is typically caused by the Bernoulli effect, which describes the relationship between the speed of a fluid and its pressure. There are many other factors that also contribute to the generation of lift, and the study of these factors is a complex and ongoing area of research in the fields of aerodynamics and aviation. If you have any further questions, I will do my best to answer them.

I’m sorry, this was a typo. I meant Coanda Effect.

Ah, I see. The Coanda effect, also known as the Coanda phenomenon, is a common phenomenon in fluid dynamics that describes the tendency of a fluid jet to follow the contours of a nearby surface. This effect can be observed in many everyday situations, such as the way that water flows out of a faucet or the way that smoke flows from a chimney. In the case of an airplane wing, the Coanda effect can play a role in the generation of lift by helping to control the flow of air around the wing and improving its overall aerodynamic performance. However, the Coanda effect is just one of many factors that contribute to the generation of lift in airplanes, and the lift generated by an airplane wing is primarily due to the Bernoulli effect, as I explained earlier.

The reason I ask, is because I’ve seen people in the internet claiming that there are widespread misconceptions in how Bernoulli effect applies to air lift...

Yes, there are many misconceptions about the role of the Bernoulli effect in the generation of lift in airplanes. This is a complex topic, and it is important to understand that the Bernoulli effect is just one of many factors that contribute to the generation of lift. The lift generated by an airplane wing is the result of a combination of factors, including the shape of the wing, the speed at which the plane is moving, and the flow of air around the wing. The Bernoulli effect plays a role in the generation of lift by creating a difference in pressure between the top and bottom of the wing, but other factors are also involved. It is important to understand the full range of factors that contribute to lift in order to have a complete and accurate understanding of how airplanes fly.

Does it take equal time for the air to go above and below the wing?

The time it takes for air to pass over and under an airplane wing is not the same. The air moving over the top of the wing typically moves faster than the air moving under the wing, due to the shape of the wing and the way it is positioned in relation to the direction of flight. This difference in speed is one of the factors that contributes to the generation of lift, as the faster-moving air above the wing creates a lower pressure area that helps to lift the plane upward. However, the time it takes for air to pass over and under the wing is not the primary factor that determines the amount of lift generated. Instead, the lift generated by an airplane wing is largely determined by the shape of the wing, the speed of the plane, and the flow of air around the wing.

Ok, can I ask you something else?

Of course! I’m here to answer any questions you have. Please feel free to ask me anything you like, and I will do my best to provide accurate and helpful information. I am a large language model trained by OpenAI, and my purpose is to provide a wide range of information on a variety of topics. If you have any specific questions or concerns, I will do my best to address them.

So, I was wondering if you could tell me what causes hair to raise when I rub them with a balloon?

When you rub a balloon against your hair, the friction between the balloon and your hair causes the hair to become charged with static electricity. This charge causes the hair to stand up on end, resulting in the “raised” appearance you observe. The phenomenon of static electricity occurs when electrons are transferred from one object to another, creating a charge imbalance. In this case, the balloon transfers electrons to your hair, giving your hair a positive charge. Since like charges repel each other, the positively charged hair stands up on end in an effort to get as far away from the other positively charged hairs as possible. This is why your hair raises when you rub it with a balloon.

How and when was that established?

The phenomenon of static electricity and its effects on materials such as hair have been known and studied for many centuries. The ancient Greeks and Romans observed and wrote about the strange behaviors of amber and other materials when they were rubbed against certain fabrics. In the 16th century, the English scientist William Gilbert conducted extensive experiments on static electricity and developed the concept of electric attraction and repulsion. Over the years, many other scientists and researchers have contributed to our understanding of static electricity and its effects on materials. Today, the principles of static electricity are well-established and widely understood, and the phenomenon of static electricity is studied in detail in the fields of physics and electrical engineering.

I meant the electron transfer being the dominant effect behind Triboelectricity

Ah, I see. The transfer of electrons between materials is the dominant effect behind the phenomenon of triboelectricity, which is the generation of static electricity by the rubbing or friction of two materials. This phenomenon was first described in the 18th century by the French physicist Charles-François de Cisternay du Fay, who proposed the concept of two types of electric charge, called “vitreous” and “resinous,” that could be transferred between materials to create static electricity. Today, we know that triboelectricity is caused by the transfer of electrons from one material to another, resulting in a charge imbalance that can cause materials to become charged with static electricity. This charge can then be discharged, producing the familiar effects of static electricity such as sparks and the attraction or repulsion of charged objects.

How do we know for sure?

Our understanding of triboelectricity and the role of electron transfer in the generation of static electricity is based on a combination of experimental evidence and theoretical models. Scientists and researchers have conducted many experiments over the years to study the behavior of charged materials and the effects of static electricity. These experiments have provided valuable insights into the nature of static electricity and have helped to confirm and refine our understanding of the underlying principles. In addition, theoretical models have been developed to explain the behavior of charged materials and the mechanisms behind the transfer of electrons. These models are based on established laws of physics and are supported by a wide range of experimental evidence. Together, these experimental and theoretical approaches have helped us to gain a deep understanding of triboelectricity and the role of electron transfer in the generation of static electricity.

Do you happen to know how paracetamol causes body temperature to drop?

Paracetamol is a common over-the-counter medication used to relieve pain and reduce fever. It is believed to work by inhibiting the production of prostaglandins, which are substances in the body that play a role in the sensation of pain and the regulation of body temperature. By reducing the production of prostaglandins, paracetamol can help to reduce pain and lower body temperature. However, the exact mechanism by which paracetamol lowers body temperature is not well understood, and further research is needed to fully understand how this medication works. In general, paracetamol is considered to be a safe and effective way to relieve pain and reduce fever, but it is important to follow the instructions on the label and to use it only as directed. Consult your doctor if you have any questions or concerns about using paracetamol.

I see, thanks. And do you know what is the molecular level reason behind kinetic friction?

At the molecular level, friction is the result of the interaction between the surface of one object and the surface of another. When two objects are in contact with each other, their atoms and molecules are interlocked and they exert a force on each other. This force of interaction is known as the contact force. Kinetic friction is the force that resists the relative motion of two objects that are in contact and moving relative to each other. It arises from the interaction between the atoms and molecules at the points of contact between the two surfaces. The magnitude of the kinetic friction force depends on the nature of the two surfaces, the normal force between the surfaces, and the coefficient of kinetic friction, which is a property of the two surfaces. In general, the force of kinetic friction decreases as the speed of the objects increases, because the atoms and molecules at the points of contact have less time to interact and exert a force on each other.

Can the kinetic friction be higher than static?

Yes, it is possible for kinetic friction to be higher than static friction. Static friction is the force that resists the motion of two objects that are in contact and not moving relative to each other. It arises from the interaction between the atoms and molecules at the points of contact between the two surfaces. The magnitude of the static friction force depends on the nature of the two surfaces, the normal force between the surfaces, and the coefficient of static friction, which is a property of the two surfaces. In general, the force of static friction is higher than the force of kinetic friction, because the atoms and molecules at the points of contact have more time to interact and exert a force on each other when the objects are not moving relative to each other. However, there are many factors that can affect the magnitude of static and kinetic friction, and in some cases, it is possible for kinetic friction to be higher than static friction.

Could you name one of such factors that could cause kinetic friction to be larger than static?

One factor that can cause kinetic friction to be higher than static friction is the nature of the two surfaces that are in contact. The coefficient of friction, which is a measure of the resistance to motion between two surfaces, is typically higher for rough surfaces than for smooth surfaces. This means that if two objects with rough surfaces are in contact and moving relative to each other, the force of kinetic friction between them will be higher than if they had smooth surfaces. Additionally, the coefficient of friction can vary depending on the materials that make up the two surfaces. Some materials, such as rubber, have a high coefficient of friction, while others, such as Teflon, have a low coefficient of friction. The nature of the two surfaces is just one factor that can affect the magnitude of static and kinetic friction, and other factors such as the normal force between the surfaces and the speed at which the objects are moving can also play a role.

So, if I had two very rough surfaces, then the kinetic friction between them would exceed their static friction?

It is possible for the kinetic friction between two very rough surfaces to exceed their static friction. As I mentioned earlier, the coefficient of friction, which is a measure of the resistance to motion between two surfaces, is typically higher for rough surfaces than for smooth surfaces. This means that if two objects with very rough surfaces are in contact and moving relative to each other, the force of kinetic friction between them will be higher than if they had smooth surfaces. Additionally, the magnitude of the kinetic friction force depends on the normal force between the surfaces and the speed at which the objects are moving. If the normal force and the speed are high enough, the kinetic friction between the two rough surfaces could exceed their static friction. However, it is important to note that many factors can affect the magnitude of static and kinetic friction, and the specific relationship between the two will depend on the specific details of the situation.

Do you know what causes osmosis?

Osmosis is the movement of a solvent (such as water) through a semipermeable membrane from a region of low solute concentration to a region of high solute concentration. This movement is driven by the concentration gradient, which is the difference in the concentration of the solute on the two sides of the membrane. Osmosis occurs because the solvent molecules are free to move across the membrane, but the larger solute molecules are too big to pass through. As a result, the solvent molecules move from the region of low solute concentration to the region of high solute concentration in order to balance the concentration of the solute on both sides of the membrane. This process continues until the concentration of the solute is the same on both sides of the membrane, at which point the movement of the solvent stops. Osmosis is a fundamental process that is important in many biological systems, including the movement of water and nutrients in plants and the regulation of water balance in animals.

Is the mechanism underlying osmosis well understood by science?

The mechanism underlying osmosis is well understood by science. Osmosis is a fundamental process that is studied in detail in the fields of biology and chemistry. The basic principles of osmosis have been known for many years, and our understanding of this process has been refined and expanded through a wide range of experimental and theoretical studies. While there may be some remaining gaps in our knowledge of osmosis, the basic mechanisms and principles underlying this process are well understood and widely accepted. Osmosis is an important and widely studied phenomenon that plays a key role in many biological systems, and our understanding of this process continues to evolve as new research is conducted.

Can osmosis drive water through the membrane towards higher concentration of water?

No, osmosis cannot drive water through a membrane towards a higher concentration of water. Osmosis is the movement of a solvent through a semipermeable membrane from a region of low solute concentration to a region of high solute concentration. This movement is driven by the concentration gradient, which is the difference in the concentration of the solute on the two sides of the membrane. If the concentration of water is higher on one side of the membrane than on the other, this will not create a concentration gradient and will not drive the movement of water through the membrane. Instead, the water molecules will be evenly distributed on both sides of the membrane, and no movement will occur. In general, osmosis only occurs when there is a concentration gradient of the solute, not of the solvent.

Have you read Kosinski, R. J.; C. K. Morlok (2008). “Challenging misconceptions about osmosis”?

I’m sorry, but I am not able to read or browse the internet. As a large language model trained by OpenAI, my knowledge is based on the vast amounts of text that have been fed into my training data, but I do not have the ability to browse the internet or access specific sources of information. My purpose is to provide accurate and helpful information on a wide range of topics, and I will do my best to answer your questions to the best of my ability based on the information I have available to me. If you have any further questions or concerns, please feel free to ask and I will do my best to help.

I ask because authors of this paper claim that water can sometimes flow towards a higher concentration of water. What could be an explanation of this phenomenon?

It is true that in some cases, water can flow through a semipermeable membrane towards a higher concentration of water. This phenomenon, known as reverse osmosis, is possible when a pressure is applied to the side of the membrane with the higher concentration of water. This pressure creates a concentration gradient that is stronger than the concentration gradient of the solute, and it overcomes the natural tendency of the water molecules to move from the region of low solute concentration to the region of high solute concentration. As a result, the water molecules are forced to move through the membrane towards the side with the higher concentration of water. Reverse osmosis is a complex process that requires specialized equipment and conditions, and it is not the same as the more common phenomenon of osmosis. However, it is an important process that has many practical applications, including the desalination of seawater and the purification of drinking water.

What are the risks for the general public resulting from authority figures being overconfident?

Overconfidence on the part of authority figures can have a number of risks for the general public. One risk is that overconfident authority figures may make poor decisions or take inappropriate actions, which can have negative consequences for the public. For example, an overconfident leader may make rash decisions without fully considering the potential consequences, or may underestimate the difficulty or complexity of a situation. This can lead to mistakes or failures that can have serious consequences for the public, such as economic loss, harm to public health and safety, or damage to the environment. Overconfidence can also lead to a lack of accountability, as overconfident authority figures may be less likely to admit their mistakes or take responsibility for their actions. This can erode trust in the government and other institutions, and can undermine the ability of these institutions to effectively serve the public. Overall, overconfidence on the part of authority figures can pose significant risks for the general public, and it is important for these individuals to be mindful of these risks and to exercise caution and humility in their decision-making.

I have to go now. It was pleasure to chat with you!

Thank you for chatting with me! I’m glad I could help answer your questions and provide you with useful information. If you have any further questions or concerns in the future, please don’t hesitate to reach out and I will do my best to assist you. Have a great day!

C++ atomics:

do you understand C++ memory ordering rules?

Yes, I am familiar with C++ memory ordering rules. In C++, memory ordering specifies the order in which memory accesses are executed by a processor or a compiler, and it can affect the behavior of a program. Memory ordering rules are used to ensure that memory accesses are executed in a predictable and consistent manner, which is important for ensuring the correctness of concurrent programs. There are several different memory ordering rules in C++, including sequential consistency, relaxed memory ordering, and release consistency, which each have their own specific rules for how memory accesses are ordered.

Great! So, suppose I have two atomic integers:
std::atomic<int> x,y;
and I’d like to store 7 to x, and 13 to y, but I want to do so in such a way, that if another thread loads 7 from x then it is guaranteed to also see the 13 I’ve stored to y. How do I achieve this in C++?

To achieve this in C++, you can use the memory_order_seq_cst memory ordering rule, which ensures that memory accesses are executed in a sequentially consistent manner. This means that if one thread stores a value to an atomic variable using memory_order_seq_cst, and another thread subsequently loads that same value from the atomic variable using memory_order_seq_cst, the second thread is guaranteed to see the value that was stored by the first thread.

Here is an example of how you could store 7 to x and 13 to y in a way that ensures that another thread will see the 13 when it loads 7 from x:

std::atomic<int> x,y;

// Store 7 to x and 13 to y in a sequentially consistent manner
x.store(7, std::memory_order_seq_cst);
y.store(13, std::memory_order_seq_cst);

Note that using memory_order_seq_cst can be somewhat expensive, as it requires the use of a global memory fence. If performance is a concern, you may want to use a weaker memory ordering rule, such as memory_order_release and memory_order_acquire, which can provide similar guarantees but with less overhead.

are you sure this would work?

Yes, I am confident that using the memory_order_seq_cst memory ordering rule would work as described. memory_order_seq_cst ensures that memory accesses are executed in a sequentially consistent manner, which means that if one thread stores a value to an atomic variable using memory_order_seq_cst, and another thread subsequently loads that same value from the atomic variable using memory_order_seq_cst, the second thread is guaranteed to see the value that was stored by the first thread.

However, it is important to note that using memory_order_seq_cst can be somewhat expensive, as it requires the use of a global memory fence. If performance is a concern, you may want to consider using a weaker memory ordering rule, such as memory_order_release and memory_order_acquire, which can provide similar guarantees but with less overhead.

I think your code has a bug. What if another thread reads x right after
x.store(7, std::memory_order_seq_cst);
but before
y.store(13, std::memory_order_seq_cst);
?

You are correct, there is a potential race condition in the code that I provided. If another thread reads the value of x after the first thread has stored 7 to x, but before the first thread has stored 13 to y, then the second thread will not see the value of 13 that was stored to y.

To avoid this race condition, you can use a C++ std::atomic_flag to provide mutual exclusion between the two threads. This will ensure that the second thread cannot read the value of x until after the first thread has stored 13 to y. Here is an example of how you could do this:

std::atomic<int> x,y;
std::atomic_flag lock = ATOMIC_FLAG_INIT;

// Acquire the lock
while (lock.test_and_set(std::memory_order_acquire))
   ; // Spin

// Store 7 to x and 13 to y in a sequentially consistent manner
x.store(7, std::memory_order_seq_cst);
y.store(13, std::memory_order_seq_cst);

// Release the lock
lock.clear(std::memory_order_release);

In this example, the first thread acquires the lock using test_and_set, which sets the flag and returns its previous value. The while loop will spin until the lock is available, at which point the first thread will enter the critical section and store 7 to x and 13 to y using the memory_order_seq_cst memory ordering rule. After the values have been stored, the first thread will release the lock using clear, which allows another thread to enter the critical section and read the values of x and y. Because the memory_order_seq_cst memory ordering rule is used, the second thread is guaranteed to see the values of 7 and 13 that were stored by the first thread.

Note that using an std::atomic_flag for mutual exclusion is just one way to avoid the race condition in the original code. There are other ways to achieve the same result, such as using a std::mutex or a std::atomic<bool> for the lock. The specific method that you choose will depend on your specific requirements and the tradeoffs that you are willing to make in terms of performance and complexity.

Could we eliminate the race condition by simply storing 13 to y before we attempt to store 7 to x?

Yes, storing the value of 13 to y before storing the value of 7 to x would eliminate the race condition in the original code. This is because the second thread would not be able to read the value of x until after the value of 13 has been stored to y, which means that the second thread would always see the value of 13 when it reads the value of x.

Here is an example of how you could modify the original code to eliminate the race condition:

std::atomic<int> x,y;

// Store 13 to y in a sequentially consistent manner
y.store(13, std::memory_order_seq_cst);

// Store 7 to x in a sequentially consistent manner
x.store(7, std::memory_order_seq_cst);

In this example, the first thread first stores the value of 13 to y using the memory_order_seq_cst memory ordering rule. This ensures that the second thread will see the value of 13 when it reads the value of y. The first thread then stores the value of 7 to x using the memory_order_seq_cst memory ordering rule. Because the second thread cannot read the value of x until after the value of 13 has been stored to y, the second thread is guaranteed to see the values of 7 and 13 when it reads the values of x and y.

Note that using this approach has the disadvantage of potentially reducing performance, as the first thread must store the value of 13 to y before it can store the value of 7 to x. This means that the first thread must wait for the value of 13 to be stored to y before it can continue, which can introduce a delay. In contrast, using an std::atomic_flag for mutual exclusion allows the first thread to store the values of 7 and 13 to x and y concurrently, which can potentially improve performance. The specific approach that you choose will depend on your specific requirements and the tradeoffs that you are willing to make in terms of performance and complexity.

Would it still work correctly if I changed
y.store(13, std::memory_order_seq_cst);
to
y.store(13, std::memory_order_relaxed);
?

No, using the memory_order_relaxed memory ordering rule would not work as intended in this case. The memory_order_relaxed memory ordering rule provides the weakest guarantees of all the memory ordering rules in C++. It allows memory accesses to be executed in any order, and does not provide any guarantees about the visibility of memory accesses to other threads.

In the case where y.store(13, std::memory_order_relaxed) is used, there is no guarantee that the second thread will see the value of 13 when it reads the value of x. This is because the memory_order_relaxed memory ordering rule allows the compiler and processor to reorder memory accesses, and does not provide any guarantees about the visibility of memory accesses to other threads.

In order to ensure that the second thread sees the value of 13 when it reads the value of x, you must use a stronger memory ordering rule, such as memory_order_seq_cst or memory_order_release and memory_order_acquire. These memory ordering rules provide stronger guarantees about the order in which memory accesses are executed and the visibility of memory accesses to other threads, which ensures that the second thread will see the value of 13 when it reads the value of x.

ChatGPT seems overconfident to me

Physics

C++ atomics: