The 2-inch cone of photons will spread to about 75 feet in diameter by the time it hits a moving target if it is about 500 feet away. Only a tiny fraction of those photons will actually hit a smooth surface on the target vehicle, like its front bumper. Most will hit other parts of the car plus the ground, trees, parked cars, telephone poles and other stationary objects. As a result of the Compton Effect,[13][14] the atoms in all those objects will emit and scatter new photons in many directions, and only a very tiny fraction of those new photons will actually get back to the 2-inch receiver on the radar gun. The additional returned photons verify what could theoretically have been measured by a single photon.

[13] https://en.wikipedia.org/wiki/Compton_scattering
[14] http://hyperphysics.phy-astr.gsu.edu/hbase/Relativ/photel.html

Compton scattering, discovered by Arthur Holly Compton, is the scattering of a photon after an interaction with a charged particle, usually an electron. If it results in a decrease in energy (increase in wavelength) of the photon (which may be an X-ray or gamma ray photon), it is called the Compton effect. Part of the energy of the photon is transferred to the recoiling electron. Inverse Compton scattering occurs when a charged particle transfers part of its energy to a photon.

Conservation of energy then tells us that the electron energy after the collision is 9.999744 GeV. So essentially all of the energy of the photon is transferred to the electron.

The effect is significant because it demonstrates that light cannot be explained purely as a wave phenomenon

Compton's experiment convinced physicists that light can be treated as a stream of particle-like objects (quanta called photons), whose energy is proportional to the light wave's frequency.

The difference between wavelengths of initial photon and scattered photon is known as Compton Shift.

light is always propagated in empty space with a definite velocity c which is independent of the state of motion of the emitting body.

Light propagates through empty space with a definite speed c independent of the speed of the source or observer.

He [Harry G. Frankfurt] argues that bullshitters misrepresent themselves to their audience not as liars do, that is, by deliberately making false claims about what is true. In fact, bullshit need not be untrue at all.

Rather, bullshitters seek to convey a certain impression of themselves without being concerned about whether anything at all is true. They quietly change the rules governing their end of the conversation so that claims about truth and falsity are irrelevant.

Bullshit is unavoidable whenever circumstances require someone to talk without knowing what he is talking about. Thus the production of bullshit is stimulated whenever a person’s obligations or opportunities to speak about some topic are more excessive than his knowledge of the facts that are relevant to that topic. This discrepancy is common in public life, where people are frequently impelled— whether by their own propensities or by the demands of others—to speak extensively about matters of which they are to some degree ignorant. Closely related instances arise from the widespread conviction that it is the responsibility of a citizen in a democracy to have opinions about everything, or at least everything that pertains to the conduct of his country’s affairs.

One night, I was not able to sleep in my usual sleeping quarters because of a technical problem and had to find a place on the ISS to camp out. I picked the PMM, our storage module. After setting up my sleeping bag and closing my eyes, I began to feel my heart race and lips tingle—my CO2 symptoms. I realized the ventilation in that module wasn’t good enough, and after relocating my sleeping bag several times, I gave up and moved out into the main hallway, Node 1. It was a poignant lesson in the importance of ventilation, because in space there’s no atmospheric circulation without electric fans. Without ventilation an astronaut would create a cloud of CO2 as he breathed, and unless he moved, he would slowly die.

I’ve been very fortunate in my career. I’ve done some pretty crazy and hair-raising things. Flown F-16s over Iraq and Korea. Piloted a space shuttle. Flown a rendezvous mission. Done spacewalks. But in all seriousness, by far, without a doubt, the most stressful thing I’ve ever done in my life was cut [fellow astronaut] Samantha[ Cristoforetti]’s hair. Because if I’d screwed that up there would have been millions of Italians angry at me. And that’s probably not survivable.

And just in case you were wondering about number two in a diaper? The answer is no. Not ever. I’ve never heard of it and just can’t imagine it happening unless under the direst of circumstances. You’d do anything in your power to prevent that situation. So, that answers that question.

One of Mr. Einstein’s most profound insights was that the speed of light is always constant, no matter how fast you’re moving, everywhere in the universe (black holes are problematic for some laws of physics, but that’s a topic for another book, one written by a proper physicist and not a fighter pilot). To illustrate this concept, consider two trains moving toward each other, each traveling 50 kph. If you are riding on one, it appears that the other train is moving at 100 kph toward you. However, if you shine a light beam at someone on the other train, you will measure its speed as it leaves your flashlight as 300,000 kilometers per second, and when that light beam hits him, he will also measure it as 300,000 kilometers per second. He won’t perceive the light as traveling that extra 100 kph. No matter where you are or what speed you are traveling, light always appears to travel at the exact same speed. Even if both trains were traveling at 99 percent of the speed of light, a passenger on the other train would still measure your light beam as hitting them at the normal speed of light. Bizarre, but true.

Light propagates through empty space with a definite speed c independent of the speed of the source or observer.

  

November 22, 2021 - I finally got around to mentioning my science-fiction novel "Time Work" on the Science Fiction Facebook forum.  They have (or had) some rule that you can't mention a book you wrote until after you've initiated 25 or 50 threads on other subjects.  I lost track of how many threads I'd started, and yesterday I decided to just start a thread about "Time Work."  New threads have to be approved by a moderator before they will appear on the forum.  The thread appeared this morning. It just included this image of the front and back covers:

And this brief comment:

If time travel interests you, you might enjoy my novel "Time Work" which is available at Amazon.

Inventor Kyle Rawlins is asked by this brother, the President of the United States, to look into a new Anti-Time invention which allows a person and/or a camera to go back in time one second per second.  In theory, it could quickly solve nearly ALL crimes, since you could go back and FILM what actually happened and who did it.  While getting a demonstration by the inventors of the device at the scene of a recent crime, the laboratory where the device was built is bombed from a helicopter.  The investigation of that bombing leads to clues to a truly major crime of national importance that has not yet happened.  Kyle and the inventors of the device then work to prevent the pending crime from happening. 

It was fascinating to think about Anti-Time and the idea that you can go back in time, but you cannot change ANYTHING. That means you cannot even bend a blade of grass in the past. So, walking on grass is like walking on ice picks.

And since you can only go back one second per second of your time, you need to take a sleeping bag and other supplies with you if you go back more than a few hours. Then there is the problem of not being able to open a door. You have to wait for someone in Anti-Time to open it.

"The measured Doppler effect on frequencies in a radar gun is far far larger than the relativistic time dilation effect, which is much too small for the device to measure."

"The relativistic difference in clock rates for clocks in those two vehicles is only half of the *square* of v/c."

Once more, the example of the moving room with outside and inside observers will be used. Again a light signal is emitted from the centre of the room and again we ask the two men what they expect to observe, assuming only our two principles and forgetting what was previously said concerning the medium through which the light travels. We quote their answers: 

The inside observer: The light signal travelling from the centre of the room will reach the walls simultaneously, since all the walls are equally distant from the light source and the velocity of light is the same in all directions.

The outside observer: In my system, the velocity of light is exactly the same as in that of the observer moving with the room. It does not matter to me whether or not the light source moves in my C.S. since its motion does not influence the velocity of light. What I see is a light signal travelling with a standard speed, the same in all directions. One of the walls is trying to escape from and the opposite wall to approach the light signal.  Therefore, the escaping wall will be met by the signal a little later than the approaching one. Although the difference will be very slight if the velocity of the room is small compared with that of light, the light signal will nevertheless not meet these two opposite walls, which are perpendicular to the direction of the motion, quite simultaneously.

Comparing the predictions of our two observers, we find a most astonishing result which flatly contradicts the apparently well-founded concepts of classical physics. Two events, i.e., the two light beams reaching the two walls, are simultaneous for the observer on the inside, but not for the observer on the outside.

 

Nobody gets in trouble for what they do, they only get in trouble when they get caught.  The art is in getting away with it. 

While the car engine is engaged, and the car is traveling a constant 80 mph on a straight and flat road, it is in inertial motion. It is in inertial motion because there is NO NET force acting on the car. There are indeed at least four forces acting on the car (air resistance pushing backwards, the friction between the tires and the road surface pushing the car forward — that’s where the engine comes in, the force of gravity downwards, and the force of the road pushing upward), but these forces all sum to zero and there is no net force. This net force being zero also means there is no acceleration (that’s Newton’s 2nd law), and since the acceleration is zero, the velocity is constant. That is inertial motion: no NET force, no acceleration, constant velocity.

The acceleration of an object depends on the mass of the object and the amount of force applied.

Suppose you are sitting in an airplane as it accelerates down the runway during takeoff. You feel a forward force pushing on your back, but you don’t start moving forward relative to the airplane. If you could stand in the aisle on roller skates, you would accelerate backward relative to the plane. In either case, it looks as though Newton’s first law is not obeyed. Forward net force but no acceleration, or zero net force and backward acceleration. What’s wrong? The point is that the plane, accelerating with respect to the earth, is not a suitable frame of reference for Newton’s first law. This law is valid in some frames of reference and not in others. A frame of reference in which Newton’s first law is valid is called an inertial frame of reference. The earth is approximately an inertial frame of reference, but the airplane is not.

This may sound as though there’s only one inertial frame of reference in the whole universe. On the contrary, if Newton’s first law is obeyed in one particular reference frame, it is also valid in every other reference frame that moves with constant velocity relative to the first. All such frames are therefore inertial. For instance, Figure 4.9 shows three frames of reference: that of a person standing beside the runway, that of a truck driving at constant speed in a straight line, and that of the accelerating airplane. The stationary person’s frame of reference is inertial. The truck moves with constant velocity relative to the person, so its frame of reference is also inertial. In both of these frames, Newton’s first law is obeyed. However, the airplane, which is accelerating with respect to both of these observers, is in a non-inertial frame.

An object at rest remains at rest, and an object in motion remains in motion at constant speed and in a straight line unless acted on by an unbalanced force.

In physics, the word "photon" has a single meaning, and it is what Townes Olson said: "an excitation of the quantum field of electromagnetism".

The propagation of light is best described by a wave model, but
understanding emission and absorption by atoms and nuclei requires a particle approach.

So in the final analysis, is light a wave or a particle? The answer is neither and both: light has a number of physical properties, some associated with waves and others with particles.

The concept of a light quantum, or a photon, turns out to be far more subtle and mysterious than Einstein imagined. Indeed, it is still very poorly understood. 

After Thomas Young observed the two-slit interference pattern by using light in 1801, light was thought to be a classical wave. On the other hand, the electrons discovered by J. J. Thomson were thought to be classical particles. We now know that these classical concepts of waves and particles do not adequately describe the complete behavior of any phenomenon.

Everything propagates like a wave and exchanges energy like a particle.

The police radar detector easily detects this frequency shift.

But here's another image that doesn't use the word "frequency":