Comments about the book "Modern Physisics from Crisis to Crisis" by Jimena Canales

This document contains comments about the book: "Modern Physisics from Crisis to Crisis" by Jimena Canales. 2019
https://www.academia.edu/40483152/Modern_Physics_from_Crisis_to_Crisis

• The text in italics is copied from that url
  
• Immediate followed by some comments
  

In the last paragraph I explain my own opinion.

Contents

• 3. Modern Physics: From Crisis to Crisis - page 72
• 3.1 The Modern in Modern Physics - page 74
• 3.2 The Turn of the Century (1898 – 1902) - page 75
• 3.3 The St. Louis World's Fair - page 77
• 3.4 The Eclipse Expedition - page 78
• 3.5 Einstein Simplified - page 81
• 3.6 Conventionalism and Differences with Poincare - page 83
• 3.7 Differences with Lorentz - page 84
• 3.8 Ernst Mach, The Vienna Circle, and Logical Positivism - page 87
• 3.9 Anti-Semitism and Modern Physics - page 90
• 3.10 Bergson and Continental Philosophy - page 92
• 3.11 From Husserl to Heidegger - page 93
• 3.12 Quantum Mechanics - page 96
• 3.13 Postwar Continental Thought - page 97
• 3.14 From Quine to Kuhn - page 96
• Index

Reflection

• Reflection 1 - Lorentz and time
• Reflection 2 - The laws of physics.

Relativity theory and quantum mechanics became the two most important branches of “Modern Physics” that emerged as an alternative to “Classical Physics” (a term often used interchangeably with that of “Newtonian” or “Galilean” physics).

Okay

page 73

How did the new physics affect European intellectual thought?

Okay.

Not only did new insights into the nature of the physical universe affect how intellectuals across fields thought about basic concepts (such as time, space, and the nature of matter and light), but they also had to contend with the growing status of physics as a field of knowledge in the public sphere.

Okay.

The main scientific insights of these scientific revolutions remain, for the most part, valid today.

Okay.

New laws sought to explain the universe at two extremes, microscopic and macroscopic, as the world became more extreme in other ways too.

The world is at present not more extreme at in the past. Our tools to investigate are more powerfull.

Widespread fears of the potential of science and technology running amok led to new discussions about the role of human agency within larger technological systems and networks.

okay.
This introduction does not mention the word: crisis.

3.1 The Modern in Modern Physics - page 74

A common way of understanding the main scientific purport of these fields has been in terms of their radical redefinition of traditional concepts of time and space.

Okay (?)

As is well known, the theory of relativity took time to be a fourth dimension next to the three dimensions of space.

This requires a clear definition of the concept: dimension
It should be mentioned that the fourth dimension is mostly expressed as c * t. In that case it is a distance travelled; not a physical length, like the length of a rod.

Although this insight can be found in different forms before the twentieth century (and can even be traced to ancient philosophy), Einstein’s theory of relativity introduced it alongside the more radical claim that no privileged “frame of reference” existed, that is, that for every point in space-time the laws of physics are the same, or invariant.

This requires a clear definition of the concept: The laws of physics. What does it mean?.
It should be mentioned that space-time does not exist.

These two insights were related to the discovery of time and length dilation:

Here I expect is mentioned: time dilation and length contraction.

Measurements of time and length were proven to vary in relation to the velocity of translation of a system in motion relative to another one.

In this sentence two reference frames are involved.
This requires a clear definition of how the velocity of a reference frame is measured. For example: A reference frame here on Earth and on the Moon.

Quantum mechanics changed our common perception of space and time in yet other ways.

This is a tricky sentence, because what has the behaviour of the elementary particles to do with space and time.

First, the “uncertainty relation” (associated with the work of Werner Heisenberg) posed an absolute limit on the knowledge that could be obtained (non-commuting observables such as position and momentum could not be determined beyond a certain limit, Δx Δp ≥ ħ/2)

The major problem is that from one elementary particle not both at the same time the position and momentum can be measured.
It should be understood that momentum p = m * v and v = x(t2) - x(t1) / (t2 - t1).

Second, the possibility of “non-locality” and “entanglement,” showing how one particle could affect simultaneously another one separated at arbitrarily large distances, violated the theory of relativity.

In reality this is not true.
In order to demonstrate correlation between elementary you have to perform 1000 experiments. The results should show that the correlation is -1. When this is the case when both are measured, one particle is up and the other down. The cause is the process or source when the particles are created.
To demonstrate one particle you only have to measure one. When this one is up, you can claim that the other one is down.

In addition to these revolutionary claims, scientists noted that light seemed to behave as both wave and particle, leading some scientists to advocate for a more general “theory of complementarity” where every object in the universe was considered as having both particulate and wavelike qualities.

Light, light propagation, describes a special type of physical object. It is difficult to use light in a more broader context and as something linked to all objects. Light has a color and as such a frequency. Water waves also have a frequency. Water waves can interfer which each other, but that does not mean that particles interfer which each other.
A different issue are the electrons part of each atom or molecule.

Finally, by showing how performing a measurement could change the phenomenon under investigation (as in the “double-slit experiment”), quantum mechanics introduced new questions about the relation of the universe to consciousness.

Any measurement changes something, implying that repeating exactly the same experiment is impossible.
This implies that it is impossible to calculate the speed of any particular elementary particle, because you have to measure its position twice.
The universe has no consciousness.

To explain the philosophical and physical meaning of these effects, the Danish physicist Niels Bohr developed an explanatory framework known as the “Copenhagen interpretation,” stressing indeterminism in the laws of the universe.

The evolution of any process is neither deterministic or indeterministic. The evolution is controlled from within the process.

page 75

3.2 The Turn of the Century (1898 – 1902) - page 75

Both ended up by having complicated relationships to Einstein’s proposed solution to the “crisis” of science they described, and both in many ways anticipated – but did not follow through – the research programs associated with Einstein’s work.

Okay

At the turn of the century a number of prominent scientists and intellectuals perceived that science was “bankrupt” and in “crisis.”

Okay

page 76

Signs that a crisis in science was brewing came to a tipping point when Poincaré, a highly respected mathematician and scientist, noted how, in the realm of electricity and magnetism, the laws of physics seemed radically different.

Okay

In work published in 1898 Poincaré explained how these laws showed a completely new aspect of time where it was no longer a single or unified concept and where no master clock connected to the universe could ever be found.

What is mentioned with the concept "master clock" ?

In the Revue de Métaphysique et de Morale he stated that, “Of two watches, we have no right to say that the one goes true, the other wrong; we can only say that it is advantageous to conform to the indications of the first.”

• First we should agree, that two identical clocks A and B can be considered both at rest if the distance (in 3D) does not change.
  Both clocks can be synchronized from a light source half way between both clocks. When this is done both clocks A and B show exactly the same number of clock counts.
• Secondly a third clock C, identical as A and B, can be considered which moves from A to B. When they meet Clock C is synchronized which clock A.
  
• Third when clock C meets clock B two situations can be observed:
  • When the clock count of clock C is less than clock B, this means that clock C runs slower. The conclusion is that the clock A and B are at rest and clock C can be considerd as moving.
  • When the clock count of clock C is higher than clock B, this means that clock C runs faster. The conclusion is that the clock A and B are not at rest, but are infact moving and clock C can be considerd as at rest.

3.3 The St. Louis World's Fair - page 77

Poincaré followed this presentation with the publication the following year of “Sur la dynamique de l’électron,” which he presented on June 5, 1905 to the Académie des Sciences.

Okay

Therein he explained how the “Lorentz transformations” (the new formulae of time and space describing electrodynamic phenomena central to Einstein’s theory) could be expressed in terms of the quadratic expression “x^2 + y^2 + z^2 – t^2” with “invariant” properties in a “space of four dimensions".

The real equation is: x^2 + y^2 + z^2 – (c*t)^2 = s^2. Considering c=1, should be physical justified. Space of four dimensions is not physical space. The same as space-time. It should be called mathematical space.

In both papers, Poincaré discussed the possible existence of gravitational waves and expressed how further astronomical tests would be possible.

Gravitational waves are fluctations of a gravitational field, caused by two rotating heavy objects.

Poincaré considered these insights as an important “modification” of the laws of Newton (in the shorter Comptes Rendus version) and as “analogous” to the Copernican revolution (in the longer text).

The most important insights are physical related, that means more detailed descriptions of the physical processes.

page 78

3.4 The Eclipse Expedition - page 78

page 79

Most accounts of the importance of Einstein’s work after the eclipse expedition were based on a standard model where the value of science was understood in terms of hypothesis creation, theoretical prediction, and experimental confirmation.

The theoretical prediction and experimental confirmation, part of Einstein's work, is a very complex endavour. It involves many observations and complex mathematics which should be described in detail.

The model for this kind of scientific production became popular after the French astronomer Urbain Le Verrier’s discovery of Neptune was widely publicized in 1846.

Le Verrier used Newton's Law. Einstein used the 'Einstein equations'. The second are extremely complex if no short cuts (approximations) are used

page 80

Le Verrier’s success in leading observers to find a new planet (which waeventually named Neptune) fueled a race to explain another anomaly in Newtonian celestial mechanics: the perihelion of Mercury.

Okay.

Observations of its actual movement differed greatly from the value obtained through mathematical calculations.

Using Newton's Law.

The most recent calculations using the new theories showed that the perihelion occurred “in the same direction as that which has been observed without being explained, but [was] considerably smaller” than the one obtained with a traditional (Newtonian) definition of mass.

In the case of Newton's Law there exists no definition of mass. (?) The mass of each object is calculated using Newton's Law and using observations. Mass in Newton's Law is indirectly defined as that the total force on each object is zero.

In the years that followed, Einstein decided to explore other ways to explain the observed value of the perihelion by proposing changes in mass due to velocity.

To define mass as a function of velocity is tricky. In Newton's Law mass is considered constant. What can be done is include mass loss.
The problem is easy to understand when two objects are moving in an circle around each other. In that case their speeds (each) are constant and as a consequence their masses are constant.
When their trajectories are elliptical their speeds (each) are variable and when the masses are a function of their speeds, these masses also fluctuate.
The problem is how to calculate these numbers.?
This problem is easy (?) when two objects are involved, but impossible to solve if 10 objects are considered, all moving in a more or less random pattern around each other.

In 1915 he proposed a theory that “has as a consequence a curvature of light rays due to gravitational fields twice as strong” as previously thought.

The main problem to consider is a physical problem.

page 81

While the three classic tests were used to prove General Relativity, after 1907 Einstein increasingly invoked the Michelson–Morley experiment as evidence in favor of the Special Theory of Relativity.

It is complicated to use Michelson & Morley experiment as evidence in favor of the Special Theory of Relativity.
This also requires a clear definition of STR.

Historians and philosophers of science, however, have noted that in both cases the actual reliance of Einstein’s work on experiment is more complicated than how it was presented in his scientific papers and by the press.

The experiments to demonstrate GR are very complicated. The main reason is that the mathematics used is complicated.
as Part of the problem is that the physical world we observe is not the physical reality. The physical processes evolve in a physical time, as part of the physical reality, as a colossal set of events, and all these events happen simultaneous. All these events, every where in the universe are happening now. Each of these events is caused by previous events (in the past) and are the cause of other events (in the future).
To simulate this process we should imagine that every point in the universe is linked to a virtual clock. These clocks allow us to monitor the time and position of every event, specific events which also create a lightsignal.

3.5 Einstein Simplified - page 81

The astronomer asked readers to imagine an aviator traveling at 161,000 miles per second, about nine-tenths the speed of light.

The first question that should be answered is: how is this speed measured.?
What you need are two clocks, a fixed distance apart, which are sysnchronized.
The second question to imagine a second aviator which travels at a speed of 161,000 miles per second, in opposite direction. It is important to realize that the distance between these two aviators is 322,000 miles after 1 second, and increases lineair at a higher speed than the speed of light.

The aviator’s watch would seem, to a stationary observer, to tick twice as slowly.

For any observer it is very difficult (impossible) to observe the ticking rate of a moving clock.
Very important is a clear definition of a stationary observer. Is that an observer at rest?
The only experiment that can be performed is to start with two clocks, from a system at rest. Move one clock for 1 second to the right with a speed of 161,000 miles per second. Move that same clock for 1 second in the opposite direction with a speed of 161,000 miles per second. Compare the clock count of the two clocks.
The result will be that clock count of the moving clock will be lower.
(*) A more scientific method is to place a different third clock somewhere in the frame at rest, and synchronize this clock with the two other clocks. See also Reflection 1 - Lorentz and time

3.6 Conventionalism and Differences with Poincare - page 83

3.7 Differences with Lorentz - page 84

page 86

Nonetheless, Lorentz cautioned that "in my opinion it is not impossible that in the future this road [research on the ether], indeed abandoned at present, will once more be followed with goodresult."

That is a wise statement

He continued to search for a stable background that could serve as an anchor for an absolute concept of time, be it the ether, a concept of space that could serve as reference point, or some fixed stars in the universe.

The most important point is that you need one definition of time which is understood by all, and which is neither absolute or reletive.

He still insisted that "one may, in all modesty, call true time the time measured by clocks which are fixed in this medium [space], and consider simultaneity as a primary concept."

Identical events, the time measured of the events by these clocks, which are considered fixed in space, are considered simultaneous.

Special and General relativity were undoubtedly correct, but they were not the only way to see things: "They will just not impose themselves on us so much as the only possible ones."

It is very important to define what Special and General relativity are. Both should be merged in one theory based on the concept that all measurements are based on clocks which are fixed in space.

The differences between a "physicist of the old school" and the "relativist" resided in the fact that, while both agreed that nobody could "make out which of the two times is the right one," the old-school physicist was ready to acknowledge that he "preferred" one of them, whereas, for the relativist, "there cannot be the least question of one time being better than the other."

Finally 'you' should decide that we work with one. The problem is there exists only one universe and this universe flows from one 'now' to a next 'now', each as one event in history, each with its own time.

Lorentz's personal preference was to maintain "notions of space and time that have always been familiar to us, and which I, for my part, consider as perfectly clear and, moreover, as distinct from one another."

A clear remark

While he had introduced the concept of local time, he "never thought that this had any-thing to do with the real time.

Local time should be the same real time. Both should be called: (true) time.

The real time for me was still represented by the old classical notion of an absolute time, which is independent of any reference to special frames of co-ordinates.

The main conclusion is: the true time at present is valid for the whole of the universe independent of any coordinate system.

There existed for me only this one true time."

Time is not something that exists. Time is the reading of every fixed clock in the universe. All these time readings should indicate the same time.

Lorentz continued to believe in his hypothesis: "Asked if I consider [my hypothesis] a real one, I should answer ' yes.' It is as real as anything we observe."

Okay. However all human observations should be considered critically.

3.8 Ernst Mach, The Vienna Circle, and Logical Positivism - page 87

In an article pub-lished for general audiences in Die Kultur der Gegenwart (1915), he argued against the view that considered a decision on the merits of his theory versus competing interpretations as a matter of choice.

He, Einstein is right. It requires argumentation.

Mach had earlier argued that the most parsimonious theories described the world most accurately, and Einstein explained the benefit of his work over Lorentz's in these terms.

It is very difficult to compare Einstein's theory with Newton's theory (Newton's Law) based on which one is the simplest.
Einstein's theory should be more accurate, but it is definite not simple.
One very important consideration is, how to perform measurements in reality.

Because there were no “physical grounds (accessible in principle to observation)” for selecting a privileged frame of reference, that concept should not be used.

To perform science you need a frame of reference or coordinate system. At least one?
To evaluate this sentence you need a clear defintion of "reference frame " versus "privileged frame of reference".

“A worldview that can do without such arbitrariness is preferable, in my opinion,” he concluded, citing Mach.

More information is required to understand this sentence about
From a practical point of view, to use only one reference frame, seems the most practical. For example: one reference frame to describe the Milky way.

Einstein employed non-Euclidian (more precisely,

Sentence continues on next page.

page 88

Riemannian) mathematics that broke with long-cherished principles (that parallel lines can never cross, that the shortest path between two points is a straight line, and so on) not because these calculating techniques were useful, but rather because the universe itself should be considered as non-Euclidean.

The Universe by itself is a physical 3D concept. Euclidean and Non-Euclidean are both mathematical concepts. To call the Universe non-Euclidean does not make sense.
The central issue is that path of a light-ray is not always straight, but can be bended. That does not mean that space is bended.
It should be mentioned that some of the light rays (photons), originating from a source A at far distance, going to an observer B, with a small BH in between, are bended. This creates a type of Halo around the BH, but does not say anything about interfering space.

Mach’s philosophical understanding of science was expanded by members of the Vienna Circle, initially known as the Verein Ernst Mach.

Okay.

For the most part, they promoted a “logical empiricist” view of science that, with few exceptions, considered Einstein’s relativity as a paragon for intellectual achievement.

In influential works, and as founders of the journal Erkenntnis, its members defended the value of Einstein’s work, the exceptionalism of science, and why science rightfully stood apart from common sense or non-expert knowledge practices.

Science has nothing to do with common sense. Science requires logical investigation of observed facts and experiments.

Einstein's own view about science and its relation to philosophy and metaphysics changed significantly throughout his life.

Okay

During the years when his theory was amply contested and before he received the accolades that would follow, he insisted on a Machian, anti-metaphysical, and objective view of science.

Okay. Specific objectivity in science is important.

But in later years he denounced Mach's approach as sterile, defended the value of metaphysics, and explained that the differences between physics and metaphysics were of degree and not of kind.

This settles more or less the issues between Newton, Mach and Einstein. Anyway Mach cann't be used as a type of yardstick.

page 89

Like Carnap, Popper was con-cerned with the problem of "demarcation," establishing clear criteria for distinguishing between scientific knowledge and unscientific or pseudo-scientific beliefs.

Carl Popper's main field, was science in general. To decide what is unscientific or not is also science.

The theory of relativity was a central example for Popper, serving as an aspirational standard for proper scientific work for years to come.

That does not imply that Newton's law was not proper scientific work.

page 90

3.9 Anti-Semitism and Modern Physics - page 90

In certain cases, the links between certain scientific views, philosophical stances, and political affiliations were clear and sometimes extreme.

The central point of view should be that science and politics are completely two indepent subjects. Specific political opinions have nothing to do with science.

page 91

Lorentz, for example, actively supported Einstein personally and professionally, despite their differences.

For example: ?

Similarly, Bergson expressed his admiration for Einstein as a person and physicist, limiting his critique to certain key points around his theory.

For example: ?

Einstein’s “Internationalism and Science” (circa 1922) cited with approval the words delivered by the chemist Emil Fischer at the Royal Prussian Academy of Sciences: “Whether you like it or not, gentlemen, science is and always will be international.”

Okay.

3.10 Bergson and Continental Philosophy - page 92

Bergson objected to the shutting out of philosophy from discussions about the nature of time during the meeting and in Durée et simultanéité.

Philosophy in general has 'nothing' to do with science. Philosophy by physicists, investigation how science should be done, the basic rules, is okay.

3.11 From Husserl to Heidegger - page 93

While Bergson tackled the particular interpretation of observed results and formulae, Husserl’s critique of relativity was incorporated into the general framework of phenomenology (observations N.V.)

Okay. Interesting,

In 1935, during a Vienna lecture, he enumerated problems facing science, blaming Einstein for some of them.

Silence.

Einstein’s revolution had resulted in the distancing of science from those aspects that had “meaning” for us, mainly our everyday sense of time flowing:

Einstein’s revolutionary innovations concern the formulae through which the idealized and naïvely objectified physis is dealt with.

That means, my interpretation, that Husserl blames Einstein to have to little attention for the physical reality and too much for the mathematical aspects.

But how formulae in general, how mathematical objectification in general, receive meaning ... – of this we learn nothing; and thus Einstein does not reform the space and time in which our vital life runs its course.

With receive meaning, he means, IMO, is of physical importance.
In fact, he plays the importance of mathematics down.

page 94

Similarly, in his early work, Heidegger did not argue for or against the merits of Einstein's theory, stressing instead the need to think about “the problem of the measurement of time as treated in the theory of relativity.”

The measurement of time, how to measure time, is a general problem. Time can only be measured by using a clock, but that creates a new question: if clock count is really an indication of the physical time we want to measure?

Measurement could not simply give answers about time, since it itself occurred in time.

You must more or less first give a definition what time is. Secondly how time is measured.
See also Reflection 1 - Lorentz and time Starting point of any discussion should be that there exists one 'now' or one time, throughout the whole of the universe. This now should be the clock count of a set of clocks, fixed to a grid at rest, inside the whole of the universe.
In reality only a small part of the universe is studied.

The "temporal meaning of measurement" itself had to be considered, and it had to be considered first, before anything else, since it was more basic and more essential than any derivative scientific results.

That is totally true.

Heidegger’s lecture “The Concept of Time” diagnosed a damaging divide in the two dominant ways of thinking about time: the scientific notion of time and the lived notion.

Excellent. . With scientific notion of time, I assume, he means the physical meaning of time i.e. the evolution of all processes in time. With livid notion, I asume, the human experience of time.

In this short lecture, Heidegger explained how a renewed interest in the concept of time was largely due to Einstein.

That is correct.

The physicist, argued Heidegger, used clock time.

And clock time, he repeated, was a grossly inadequate concept for understanding time: “Once time has been defined as clock time then there is no hope of ever arriving at its original meaning again,” he warned.

I would write: "At its most deepest physical meaning."

page 95

Heidegger’s “The History of the Concept of Time” was motivated by “the present crisis of the sciences,” which, like Husserl, he blamed largely on Einstein.

Initially, Heidegger’s critique of Einstein was similar to that of Bergson and Husserl, but he soon distanced himself from their approaches by rejecting purely subjective notions of lived time as much as objective ones.

Being and Time (1927) sketched a new relation of philosophy to science, and of both to rational discourse and logical structure.

Okay.

3.12 Quantum Mechanics - page 96

The conflict between relativity and quantum mechanics intensified with the political tensions of the time.

Okay

The conflict between a quantum-mechanical description of the world and a relativistic one was articulated clearly during a discussion between Bohr and Einstein at the Fifth Solvay International Conference

It does not make sense to describe the world or the universe in general by one theory.
Quantum mechanics discusses the behaviour elementary particles and GTR the movement of the objects enlarge. Both have their own problems. One common problem for both is the definition and the use of the concepts: time, simultaneous and position.

The discussion revived with renewed force questions about the role of philosophy and epistemology in science.

Epistemology in science has to do with research. Research is mainly done by performing experiments.
Philosphy in science has to do how this research and these experiments have to be done.
A typical question to answer is: To what extend is it allowed to define that the speed of light is constant, without any physical testable evidence. The problem becomes most vissible when light goes from A to B and is bended, by masses along its path.

3.13 Postwar Continental Thought - page 97

3.14 From Quine to Kuhn - page 96

Reflection 1 - Lorentz and time

The opinion of Lorentz is very impressive. See page 86 .
Starting point about a discussion about time is that we accept that there exists one universe. This universe consists of objects and the position of these objects constantly changes in time. We humans experience these changes, but generally speaking we cannot influence how these changes evolve. The only exception is the behavior of we, humans, locally
To describe and understand these changes we humans use concepts like now, coordinate system, time and clocks.

We humans also define 'now' as a point in time.
We humans also observe that the universe is in constant change i.e. that the (position and state) of the objects in the universe world are not fixed but dynamic.
The main idea should be to start from one coordinate system, fixed in space. All clocks should also be fixed in space. All these clocks, simultaneous, show the same time
When you start from this idea all moving clocks (using light signals) will run slower and all the light signals (the positions) should be measured in this fixed coordinate system.

See also 3.5 Einstein Simplified - page 81, page 94

Reflection 2 - The laws of physics.

The laws of physics is not something that exists. They are detailed descriptions of certain physical process. In many cases physical laws are expressed in a mathematical notation. A famous law is Newton's Law. A more detailed one is GTR.
At the same time people also claim that the evolution of certain processes are governed by either of these laws. That means these processes are deterministic.
Deterministic means that the outcome of a processes exactly can be predicted. That is not true.
In the case of Newton's Law the mathematics involved consists of two differential equations, initial conditions and parameters.
Newton's law is used to describe the trajectories of a set of objects. The initial conditions are the positions and velocities at a certain initial moment t0. One important parameter is the mass of each object.
The first step of any simulation is to calculate both the intial conditions and all the parameters based on observations. That is a very complex step because general speaking all observations to measure the positions of the objects are performed at different moments and the actual position depends about the distance of the object and the point of observation.
The second step is to calculate the future of the objects at a certain moment tn. The third step is to validate these positions at tn with the actual observations at tn.

In many cases physical laws are reversible. This is also true in case of Newtons Law. That means if at the initial moment all the speeds involved are reversed the same equations can also be used to calculate the past of the objects at a moment t-n
In reality it is not possible to reverse the speed of any object, that means from a physical point thet are not reversible.

Newton's Law assumes that the force gravity acts instantaneous from source (object) to destination (object). When that is the case the force of gravity points to the present position of the source. That is not true. The force of gravity points towards a position of the source in the past. This is also a reason why processes are not reversible because then the force should point towards a position in the future. (under investigation).

Chemical reactions are not (time) reversible. The 'chemical direction' is governed by the concentrations of chemical elements involved. Normally a reaction stops when a certain equilibrium is reached. This is also the case when the elements A and B produce the elements C and D. When this reaction reaches equilibrium the products C and D have to removed and more A and B have to added, in order that the process continues. Instead of removing the products C and D, the products A and B can removed and more C and D can be added. In that case, as a matter of speaking, the chemical direction is reversed. Also in this case the reaction will stop when a certain equilibrium is reached. But that does not mean that there is any form of time reversibility involved.

The simplest case to demonstrate that chemical reactions are not (time) reversible is when you want to heat or cool water. In that case both a heating and a cooling unit is required. What you want requires manual (operator) intervention. In both cases the process will progress depending on what is selected and stop if a certain manual selected setpoint is reached.

Reflection 3

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