Every object in a state of uniform motion will remain in that state of motion unless an external force acts on it.

An inertial frame of reference in classical physics and special relativity possesses the property that in this frame of reference a body with ZERO NET FORCE acting upon it does not accelerate; that is, such a body is at rest or moving at a constant velocity.

a property of matter by which it continues in its existing state of rest or uniform motion in a straight line, unless that state is changed by an external force

Me:  It takes FORCE to move a truck.

Him:  It takes net force to change a truck's speed, but it takes zero net force for a truck to remain in uniform motion.  This is grade school physics.

Me:  It takes MORE FORCE to move a truck faster.

Him:  It takes no net force at all for a truck to move at any speed.  A truck will continue to move at its current speed, regardless of that speed, as long as zero net force is applied to it.  You're just getting confused because you are (amazingly) unacquainted with the basics of high school physics.  When objects encounter other objects, such as air, they exert mutual forces on each other.  The force provided by an engine through the drive shaft and wheels is equal and opposite to the forces exerted by other objects.  Net force is required to change the speed of an object, but not to maintain any speed.  The physics inside a sealed container depends only on the net force applied, i.e., the acceleration.

Me:  Friction does not negate the force.  Friction just determines how much force must be applied for the truck to reach a given speed.

Him:  Friction is a force, just like other forces.  The total net force on a uniformly moving object is zero.  It doesn't matter what combination of individual forces are applied, as long as they add up to zero.

The first postulate asserts that all the laws of physics are the same in all reference frames moving with constant velocity relative to each other. This postulate is a sweeping generalization of the principle of Galilean relativity, which refers only to the laws of mechanics. From an experimental point of view, Einstein’s principle of relativity means that any kind of experiment—mechanical, thermal, optical, or electrical—performed in a laboratory at rest must give the same result when performed in a laboratory moving at a constant speed past the first one. Hence, no preferred inertial reference frame exists, and it is impossible to detect absolute motion.

And also the situation where one of the astronauts was jogging in the rotating part of their space ship.


  
Those centrifuges were producing artificial gravity.  There's nothing "fictitious" about artificial gravity!  The absence of a centripetal force to offset the centrifugal force doesn't make the centrifugal force "fictitious" as the textbook says.  I did a Google search for the term "inertial systems" and found a Wikipedia page titled "Inertial Frame of Reference" and it uses the term "fictitious force" 22 times!  And they even have an web page article titled "Fictitious Force."  

Then I remembered the anthrax attacks of 2001.  So, we're supposed to believe that microbiologists use a "fictional force" when they use centrifuges to separate anthrax spores from growth and nutrient debris?  Really?

Groan!  The situation is worse than I thought!  And that makes me think that the paper I had begun writing about "Radar Gun Relativity Experiments" is more important than a paper about "Inertial and Non-Inertial Systems," and I really really need to find some way to get experiments done with a Type-1 radar gun.

November 15, 2019 - Another groan!, but also a Wow!  My subconscious awoke me again this morning with a new realization.  This time it woke me at 3:30 a.m., but I managed to get some sleep after my conscious mind finished thinking things through.  Suddenly I feel I need to write another new paper, before I write the new paper about my radar gun experiments.  The new new paper will probably be titled "Inertial and Non-Inertial Systems."

I recall reading a college textbook that stated that there are two types of systems, inertial systems and accelerating systems, in which Relativity experiments can be performed.  I remember arguing with someone that the train in Einstein's thought experiments was neither an inertial system nor an accelerating system.  It wasn't "inertial" because it was moving under power, an engine was pulling the car in which the experiments were being performed, and it wasn't "accelerating" because the engine was pulling the train at a constant speed.

The arguments I got from the mathematicians on the sci.physics.relativity discussion forum was that a train that is under power and is moving at a constant speed is "inertial."  And they believe that Einstein's FIRST Postulate says that all experiments work the same way in all inertial systems.  They specifically argue that the length of a second cannot be different in one inertial system versus another because that would violate Einstein's First Postulate: "the same laws of electrodynamics and optics will be valid for all frames of reference for which the equations of mechanics hold good."  

It wouldn't, of course.  A variable length of a second will produce different results in different "inertial systems" and "frames of reference," but no law of electrodynamics and optics would be broken, and all equations of mechanics would still hold good.   1+1=2 is just as valid as 1+3=4.

What I woke up thinking about this morning was gravity.  Suppose you have a true inertial system in a space ship coasting through space at 100,000 mph and a second system which mathematicians consider to also be "inertial," a train moving across a desert at a constant speed of 60 mph.  Virtually every experiment performed in those two "inertial" systems will produce different results.  The simplest experiment to perform to confirm that is dropping a ball to the floor from a height of 6 feet.  In the space ship, when you release the ball, the ball will remain where it is.  It will NOT fall.  There is no gravity to pull it downward.   On the train, the ball will fall to the floor.  The ball is affected by a significantly different amount of gravity on the train.  The results of those two experiments couldn't be more different, yet according to mathematicians they are both performed in an "inertial system" and cannot produce different results without violating Einstein's FIRST Postulate.

As I now see it, an "inertial system" can only exist in space, and there are several  different "non-inertial systems" in which us Earthlings can perform experiments, including an "accelerating system," which all will produce different results. 

I just need to find the time to write it all down in the form of a scientific paper.    

November 14, 2019 - Groan!  At about 4:30 this morning, my subconscious mind woke up my conscious mind to ask a question:  If radar guns emit waves that look like this:



what would happen if you tried to measure the speed of the whirling blades of a floor fan through the wire grid that surrounds the moving parts of the fan?


 
It's not a problem with photons.  Photons are extremely small, they travel at the speed of light to a blade, and before the blade can change position, atoms in the fan blade almost instantly emit NEW photons back to the gun.  The difference in the oscillation rates of the photon's energy fields sent-versus-received determine the speed of the blade.  Since even different parts of the tips of the blades move a different speeds, the gun measures the fastest speed.  Photons that hit the metal wire grid measure the grid to be stationary.

How would that work with waves?  First you have the problem of the wire grid.  If microwaves were like the waves shown above (or like water waves), the waves are going to break into a kazillion tiny waves like the double slit experiment with hundreds of slits.  The double slit experiment:

Set radar to Receive Only mode and scan for interference at operation site.

The Range Control is actually the receiver sensitivity setting. Long range, most sensitive, may make the radar susceptible to local interference. 

Type-1 radar guns do just one measurement.  They emit photons to the target and receive photons back from the target.  The gun then measures the difference in the oscillation frequencies of the emitted and received photons and computes the speed of the target.  Type-1 radar guns are considered to be “stationary only” guns, evidently because they produce controversial results when moving.

Type-2M radar guns do two measurements: (1) They measure the speed of a target and (2) they measure the speed of the gun.  They were designed and built to be used while moving.  When traveling at 60 miles per hour toward an approaching target that is traveling at 70 miles per hour, the gun will show a “patrol speed” of 60 mph and a “target speed” of 70 mph.

Type-2S radar guns also do those same two measurements.  However, Type-2S radar guns are intended to be used only while stationary.  When traveling at 60 miles per hour toward an approaching target that is traveling at 70 miles per hour, the gun will show a “relative” speed of 130 mph.  The gun has no ability to show two speeds.  If you use such a gun while moving, you need to logically figure out for yourself what speed the gun is displaying.   

Type-1 radars seem to be relatively few in number.  I was able to tentatively identify only one Type-1 radar gun, the fairly popular Stalker II SDR manufactured by Applied Concepts, Inc., in Richardson, Texas.  However, there could be others.  The Stalker II SDR’s list price is $1,600.

  

“I want to emphasize that light comes in this form—particles. It is very important to know that light behaves like particles, especially for those of you who have gone to school, where you were probably told something about light behaving like waves. I’m telling you the way it does behave—like particles."

[A tuning fork] "vibrates which means the speeds of the tines are constantly changing at the frequency of the fork in a sinusoidal fashion. In addition, the max magnitude of the vibration depend on how hard the fork is struck.

"7.4 Fan Interference
Fan interference is the most common form of interference that you
are likely to experience. It is caused when the radar measures the
speed of the vehicle blower fan. Changing the fan speed causes a
proportional change in the display speed. To correct this, relocate the
radar gun so it does not display spurious speeds or turn off the fan
motor."

3. Perform the internal test sequence by pressing the TEST button.
The unit should display 60 mph.  You will also hear an audio tone
if the volume is turned up because a 60 mph signal is being sent
through the circuitry to perform the unit's internal check.  On
release of the TEST button, 8.8.8. should be displayed to verify
display operation.

4.  Perform system check with certified tuning fork by striking the
fork until is rings then place it about 2 inches in front of the lens.
Pull the trigger and the unit will read the speed inscribed on the
fork.

The beam width of a TS3 is 12 degrees, so it sees MUCH MORE to the side than you look at when you point it.

I suddenly realized the primary difference between the Type-2M and the Type-2S radar guns.  It's obvious!

Type-2M radar guns perform TWO measurements and SHOW THEM BOTH.  The guns have ways to display "Patrol Speed" AND "Target Speed."  There's a video here about a Type-2M radar gun: https://www.youtube.com/watch?v=XlnYO_G_IxA

Type-2S radar guns also perform TWO measurements but, since the guns are intended to be used "stationary only," they just show ONE speed, which SHOULD BE the target speed.  If you use such a gun WHILE MOVING, you have to FIGURE OUT LOGICALLY for yourself what speed it is displaying.

Also, the fact that the Type-2S gun doesn't need all the hardware and
software required to show two speeds means it can be made for less cost.  That is undoubtedly one reason you can buy a Type-2S for around $100.

I'm thinking of buying one for a science experiment, but I'm wondering how it works while moving.

Have you ever used it in a moving vehicle, pointing it out at the ground or at highway signs ahead? The operator's manual says that it will show "the speed of the vehicle you are in." I'm wondering if it shows the speed of the vehicle you are in, or if it shows the speed of the gun.

So, what I would need to do is first point it out at the ground ahead and then lift it to point it at about a 30 degree angle toward empty sky. If it still shows the speed of the vehicle, it isn't showing the speed of the vehicle, it is actually showing the speed of the gun. I'd buy the gun if it shows the speed of the gun when pointed at the sky ahead. I wouldn't need it if it shows no speed when pointing at the sky ahead

I've used it in a vehicle clocking the speed of on coming traffic. From what I've experienced it wouldn't read anything if pointed at the sky as the radar waves would have nothing to bounce back from.

 

What a coincidence. I bought the Velocity myself a little while ago, just before the last time you ran away.

I have done a few experiments myself.

I was going to wait until I made a Youtube video but I thought it may be all for naught since you disappeared.  But a quick summary so far:

The Velocity records the highest speed seen while the trigger is held down.

When used as intended, stationary, it records speeds as expected.  When a car appearing to do about 50 is approaching, the stationary gun does display 50.

When used from a moving car: (not used as intended):

No other traffic around:

The gun displays my speed. This is as expected as the reflections from the road, trees, parked cars etc. is Doppler shifted to my road speed in the frame of the gun (which is moving at my road speed).

Oncoming traffic:
Oncoming traffic is displayed as moving at a high speed. If I am going 45 on a road with a speed limit of 45, oncoming traffic results in speeds around 90 or so.

Following traffic:

The gun almost always displays my road speed.  This is because the reflection from cars in front of me is that of the speed difference and that is always lower than the ground speed reflection, unless a real speeder passes me (hasn't happened yet).

Careful aim when passing a slow box truck sometimes displays a low speed.  This has happened twice, and only when (apparently) the ground reflection isn't strong enough.

Inside a moving box truck:

Not quite, but I did bring it onto a commuter rail train. (Fortunately at the end of the line so I moved into an empty car so passengers wouldn't be worried about this guy with a radar gun walking around).  The cars are metal with windows, including windows in doors between cars but enough metal for this purpose.

Front of car aiming to rear of train: No reading.
Rear of car aiming to front: No reading.
Aiming at ground out window: A speed consistent with the apparent speed of train. (also changed the angle to see cosine effect in action).

Summary: 100% consistent with what is expected from SR and Einstein's predictions, allowing for the fact the gun displays the highest speed, not necessarily the current speed. 

Click HERE to go to my notes about scientific topics discussed on this web site.

 

In case you do not recognize it, that is the Earth in the sky in the background, and the picture was supposedly taken on the moon.  Obviously, it is a fake, but I couldn't find any originals for it when I did a Google search.  Hundreds of pictures were taken by astronauts while they were on the moon, but I have only a couple hundred in my collection.  I do not have any shots that match the rocks in the foreground, nor the mountains in the background as seen from that angle.   The Earth would not appear that bright or that large when photographed from the moon's surface. The shot of the Earth by itself was evidently taken from orbit around the moon.  The part of the Earth that is in shadow indicates the sun is directly overhead when viewed from the moon, while the shadows of the rocks in the foreground show the sun is at an angle off to the left.  Oh yes, and there are no dogs on the moon.

I was able to find this actual shot taken of the Earth as seen from the surface of the moon:



A few days later, my sister sent me this image:



Researching it, I think it was taken in India.  It's totally real, of course, but it must have taken a lot of planning to capture the moon from the right angle and the right distance to make it appear like the moon is setting inside the dish of a radio telescope.   The version my sister sent me had a headline on it that said "NASA caught taking down the moon for repairs."

October 27, 2019 - While eating breakfast yesterday morning, I finished reading another book on my Kindle.  The book was "How We Got To Now: Six Innovations That Made the Modern World " by Steven Johnson.

The book is similar to Fifty Inventions that Shaped the Modern Economy, which I finished reading on October 9, except that this book is more about how one invention or discovery enables other inventions and discoveries to happen.  The "six innovations" are listed as Glass, Cold, Sound, Clean, Time and Light, but they might be better described as Making Glass, Refrigeration, Recording Sound, Bathing and Sewage Disposal, Measuring Time, and Creating Light.

I only highlighted and saved 6 pages of notes, but that isn't because the book had little worth quoting, it is because the ideas described in the book generally cannot be stated in a few words because they are about how one idea leads to another and another.  Human use of glass, for example, began as a gem or ornament, with the first sample of it being found in King Tut's tomb.  It was a piece of glass created by some unknown event which occurred about 26 million years ago in or over the Libyan desert.  It was some kind of event (probably a meteor strike) that caused temperatures on the ground to rise to well over 1,000 degrees, which resulted in melting many square miles of sand, which in turn created acres of glass globules.  Millions of years later, someone picked up a scarab beetle-shaped globule and fastened it in the center of a pendant worn by King Tut:

  

Later, of course, glass was put to many other uses, from windows to fiber optics.  The book also describes how the printing press resulted in producing books at much lower prices, which resulted in a lot of people realizing they were farsighted, which caused a demand for reading glasses, which later led to microscopes.

Refrigeration began in the mid-1800s when a man named Frederick Tudor thought it would be a profitable idea to ship blocks of ice cut from a frozen lake in wintry New England to islands in the Caribbean, so people there could have something cold to help them ward off the oppressive heat. Tudor knew that ice would keep for a long time if it was kept out of the sun and insulated with sawdust.  He figured ice would be priceless in the heat of the tropics.  But, when his ship full of ice arrived in the Caribbean, no one knew what to do with it.  It took years for a popular demand to be created for ice.  The book says,

Sugarcane, coffee, tea, cotton—all these staples of eighteenth-and nineteenth-century commerce were dependent on the blistering heat of tropical and subtropical climates; the fossil fuels that now circle the planet in tankers and pipelines are simply solar energy that was captured and stored by plants millions of years ago. You could make a fortune in 1800 by taking things that grew only in high-energy environments and shipping them off to low-energy climates. But the ice trade—arguably for the only time in the history of global commerce—reversed that pattern.

When Thomas Edison completed Scott’s original project and invented the phonograph in 1877, he imagined it would regularly be used as a means of sending audio letters through the postal system. Individuals would record their missives on the phonograph’s wax scrolls, and then pop them into the mail, to be played back days later.  Bell, in inventing the telephone, made what was effectively a mirror-image miscalculation: He envisioned one of the primary uses for the telephone to be as a medium for sharing live music. An orchestra or singer would sit on one end of the line, and listeners would sit back and enjoy the sound through the telephone speaker on the other. So, the two legendary inventors had it exactly reversed: people ended up using the phonograph to listen to music and using the telephone to communicate with friends.

In today’s world, we think of hygiene in fundamentally different ways. The concept of bathing, for instance, was alien to most nineteenth-century Europeans and Americans. You might naturally assume that taking a bath was a foreign concept simply because people didn’t have access to running water and indoor plumbing and showers the way most of us in the developed world do today. But, in fact, the story is much more complicated than that. In Europe, starting in the Middle Ages and running almost all the way to the twentieth century, the prevailing wisdom on hygiene maintained that submerging the body in water was a distinctly unhealthy, even dangerous thing. Clogging one’s pores with dirt and oil allegedly protected you from disease. “Bathing fills the head with vapors,” a French doctor advised in 1655. “It is the enemy of the nerves and ligaments, which it loosens, in such a way that many a man never suffers from gout except after bathing.”

Elizabeth I bothered to take a bath only once a month, and she was a veritable clean freak compared to her peers. As a child, Louis XIII was not bathed once until he was seven years old. Sitting naked in a pool of water was simply not something civilized Europeans did; it belonged to the barbaric traditions of Middle Eastern bathhouses, not the aristocracy of Paris or London.

If you worked for an hour at the average wage of 1800, you could buy yourself ten minutes of artificial light. With kerosene in 1880, the same hour of work would give you three hours of reading at night. Today, you can buy three hundred days of artificial light with an hour of wages.

Don’t be trapped by dogma—which is living with the results of other people’s thinking. Don’t let the noise of others’ opinions drown out your own inner voice. And most important, have the courage to follow your heart and intuition.

And I would need to explain exactly what is going on.  Unfortunately, it is extremely difficult to translate all the mathematical equations into simple explanations.  And I'm reading through scientific paper after scientific paper to see if I can find a simple way to explain things.

It took me all morning just to write this comment about what I'm trying to do.  And I cannot be absolutely certain it is entirely correct.  I've been tempted several times to just forget about writing a comment for today, or instead just write a comment about all the attempts that have been made by hackers in the past two days to POST unwanted stuff onto this web site.  Here's a screen capture of a slew of attempted POSTS that were made two days ago:

 

The attempted POSTS are from all around the globe, but they were obviously coordinated to hit at about the same time, from 4 pm to 5:30 pm.  The IP numbers that begin with 185 are mostly from Amsterdam, Holland, but one is from Odessa in the Ukraine.   (I block all attempted accesses from IP addresses beginning with 185 because they all seem to belong to hackers.) 158.69.182.99 traces back to Beauharnois, Quebec, a place that seems loaded with hackers.  27.153.202.150 traces to Putian, China.   109.70.100.23 traces to Vienna, Austria.  104.192.84.71 traces to Los Altos, California.  Except for the ones from IPs beginning with 185, there is no other pattern than that they all seemed to have hit at the same general time.  I have no idea what is going on.  And I cannot find anyone else who seems to care.  It is evidently just a routine part of having a web site.

October 22, 2019 - Every morning, as part of my startup routine, I check the latest image on NASA's Astronomy Picture of the Day web site.  Over the years I've downloaded and saved 1,717 images from the site, which is probably less than a third of total number of pictures I've viewed on the site.  This morning's Picture of the Day is the image below (you should be able to right click on it to view the full size image).



It's a "picture" taken of a man standing on "the world's largest mirror" in Bolivia. The accompanying explanation for the picture says:

Explanation: What's being reflected in the world's largest mirror? Stars, galaxies, and a planet. Many of these stars are confined to the grand arch that runs across the image, an arch that is the central plane of our home Milky Way Galaxy. Inside the arch is another galaxy -- the neighboring Large Magellanic Cloud (LMC). Stars that are individually visible include Antares on the far left and Sirius on the far right. The planet Jupiter shines brightly just below Antares. The featured picture is composed of 15 vertical frames taken consecutively over ten minutes from the Uyuni Salt Flat in Bolivia. Uyuni Salt Flat (Salar de Uyuni) is the largest salt flat on Earth and is so large and so extraordinarily flat that, after a rain, it can become the world's largest mirror -- spanning 130 kilometers. This expansive mirror was captured in early April reflecting each of the galaxies, stars, and planet mentioned above.

Following from this Equations (8) and (14) indicate that for an observer moving at a constant speed v relative to the ECI [Earth-Centered Inertial] frame, the speed of light from a source fixed in the ECI frame relative to that moving observer is c - v for the observer moving away from the source and c + v for the observer moving towards the source.

The principle underpinning modern physics, which states that the speed of light is constant and independent of the motion of the source and the observer, is shown to be invalid.

Based on classical velocity composition, when the Earth is at position A moving away from Jupiter, the speed of light relative to Earth is
(c – v) and not c as required by Einstein’s law of light propagation.

Similarly, when Earth is at position B moving toward Jupiter, the speed of light relative to Earth is (c + v) and not c as required by Einstein’s law of light propagation.

Yet despite all this weirdness, quantum physics is wildly successful at describing the world—much more so than simple old Newtonian physics (which was already pretty good). Without quantum physics, we wouldn’t have any understanding of why diamonds are so hard, what atoms are made of, or how to build electronics. So wave functions, with their numbers scattered across the universe, must somehow be related to the everyday stuff we see around us in the world, otherwise quantum physics wouldn’t be any good at making predictions. But this makes the measurement problem even more urgent—it means there’s something about the nature of reality that we don’t understand.

So how should we interpret this strange and wonderful theory? What story is quantum physics telling us about the world?

Rather than answering that question—which seems like it would be difficult—we could deny that it’s a legitimate question at all.

Physics is the science of the material world. And quantum theory purports to be the physics governing the most fundamental constituents of that world. Yet the Copenhagen interpretation says that it’s meaningless to ask about what’s actually going on in quantum physics. So what is real? Copenhagen’s reply is silence—and a look of stern disapproval for having the temerity to ask the question in the first place.

This is, at best, a profoundly unsatisfying answer. But this is also the standard answer. The physicists who pursued the question anyhow—physicists like Einstein, and later on, Bell and Bohm—did so in open defiance of Copenhagen. So the quest for reality is also the story of that rebellion, a rebellion as old as quantum physics itself.

“The idea of an objective real world whose smallest parts exist objectively in the same sense as stones or trees exist, independently of whether or not we observe them,” Heisenberg said, “is impossible.” How, then, does our world of stones and trees emerge from the world of atoms and molecules? “The transition from the ‘possible’ to the ‘actual’ takes place during the act of observation,” said Heisenberg. And what happens when we’re not looking? According to Heisenberg, that question can’t even be asked. 

Richard Feynman pointed out that although there’s no experimental way to tell the difference between two mathematically equivalent theories (i.e., two different interpretations of the same math), subscribing to one theory or the other makes a huge difference in how you think about the world. That difference, in turn, affects the new ideas and new theories we develop.

The Einstein-Bohr debates have entered into the lore of physics itself, and the usual conclusion is that Bohr won, that Einstein’s and Schrödinger’s concerns were shown to be baseless, that there is no problem with reality in quantum physics because there is no need to think about reality in the first place.

Physics is about the world around us. It aims to understand the fundamental constituents of the universe and how they behave. Many physicists are driven to enter the field out of a desire to understand the most basic properties of nature, to see how the puzzle fits together. Yet, when it comes to quantum physics, the majority of physicists are perfectly willing to abandon this quest and instead merely “shut up and calculate,” in the words of physicist David Mermin.

More surprising still is that this majority view has, time and again, been shown not to work. Despite the popular view among physicists, Einstein clearly got the better of Bohr in their debates and convincingly showed there were deep problems that needed answering at the heart of quantum physics. Simply dismissing questions about reality as “unscientific,” as some of Schrödinger’s opponents did, is an untenable position based on outdated philosophy.

the defenders of the Copenhagen interpretation presented a united front despite their private disagreements, while the rebellion, unable to agree on a single position, fizzled out.

Be sure that not only me, but the whole physics community would accept the result of that experiment, after checking the conditions and statistical analysis of the results.
For sure, you are aware of how real experiments are performed and how to perform the experiment, are you not?

    Einstein was greatly influenced by the philosopher-physicist Ernst Mach who was an advocate of logical positivism. According to logical positivism, physics should only make statements about phenomena which could be directly observed and measured. Using logical positivism as his guide, Einstein simply stated: "Time is what we measure with a clock".  According to Einstein, there was no place in physics for philosophical musings about the nature of time — all that was important was what could be measured.
    This statement of Einstein is particularly important because the theory of special relativity states that a clock which is moving will appear to run at a slower rate than a clock which is stationary. And, as Einstein stated that "Time is what we measure with a clock", this would appear to indicate that time itself runs slower for an observer who is moving relative to a secondary observer.

In the more general sense, the more recent development of the so-called Copernican principle states that no particular point in the universe (not just the Earth) can hold a privileged position in the universe. This heralds a move away from an absolute system of science and cosmology to a science which realises that no observer holds a privileged position, and that the universe is built on relative measures. The repercussions of the Copernican principle are rippling through science to this day, perhaps having its greatest impact in the theory of relativity: if no observer holds a privileged position, then all motion must be described relatively. If you have read my previous two books you will know I have a firm conviction that the universe is built on fundamental principles — principles which are "obviously correct" and would have to be true in any conceivable universe. The Copernican principle is surely another of these fundamental principles: surely no point — and therefore no observer — holds a privileged position in any conceivable universe.

Galileo's greatest contribution to the world of science was his scientific method. Before the scientific method was introduced, the proclamations of ancient philosophers such as Aristotle were accepted without question as representing the absolute truth about Nature. Galileo was one of the first scientists to challenge the wisdom of the ancients. Galileo's introduction of the scientific method allowed Nature to speak for itself. Aristotle was no experimenter, and he relied too much on his preconceptions. Famously, Aristotle once proclaimed that women have fewer teeth than men. Because no one thought to check this proclamation of Aristotle, for a thousand years everyone believed that women have fewer teeth (women and men, of course, actually have the same number of teeth).

The only conclusion which is left to us is that reality itself is different for both Alice and Bob! In Alice's version of reality, the lightning bolts hit the ground simultaneously. In Bob's version of reality, the lightning bolts did not hit the ground simultaneously. Reality is a relative concept for the two observers. This extraordinary outcome of the experiment is called relativity of simultaneity.

If I am moving relative to you, then my reality is different to your reality.

If you remember, Galilean relativity states that the laws of motion are the same for all observers who are moving at a constant velocity. There is no experiment you could perform to determine if you were stationary or moving at constant velocity.

In the discussion of the block universe in the previous chapter, it was described how all times are equally real and there is, therefore, no special "now" pointer which moves through time at a certain speed and determines the current moment. Even though we derived this result in a logical manner, there still lingers a considerable amount of resistance to this model. For example, Lee Smolin recently devoted an entire book, entitled Time Reborn, in an attempt to refute the block universe. The main reason I feel that many people have such a problem accepting the block universe model is not through any rational scientific basis, but because they instinctively feel a special "now" moment. This feeling is so utterly entrenched into our lives and psyche that it is an incredibly hard habit to break.