We all know the story. Newton said time is absolute. Einstein said time is relative. A tale so ingrained and unquestionable, that bringing it up for any reason other than the setup to a meme might seem pointless.
But I would like to show you that this story is not the whole truth.
Newton
Let’s start with Newton, who has this to say, on page 6 of the Principia:
Newton introduces his physics to the world by saying that the “common people” only understand space and time by how they relate to the senses. In other words, prior to him, people only thought of time and space as relative. Or at least that’s what he’s claiming.
He continues:
We see here that Newton very explicitly says there are two types of time, one of an absolute nature and one of a relative nature, involving measurements and observations. And he provides similar definitions for absolute space and relative space.
While it can be debated what he meant precisely, it should be clear that simplifying his position to “time is absolute” does not tell the whole story.
I posted parts of the above quote by Newton in a tweet to Ethan Siegel and this was his response:
This is not meant to be a criticism of Dr. Siegel, who is kind enough to reply, just to illustrate how persistent this story is.
We can see that in Newton’s work, right on page 6, he explicitly defines what he means by space and time. There is nothing tacit about it. But these words rang a bell.
Einstein
We find in the book Relativity, by Einstein, page 32, the following:
There’s the same “tacit assumption”, but with a twist. Einstein had written “it had always tacitly been assumed in physics that the statement of time had an absolute significance”, whereas Siegel modifies the general “in physics”, to be specifically “in Newton’s work”, which I hope I have shown is not the case.
It appears from the quotation by Einstein that he is in fact claiming time to be relative, and only relative. That is a fair impression to get from this quote, and it seems that even Einstein’s contemporaries would have gotten a similar impression.
Here is Heisenberg’s account of a discussion with Einstein:
It could be interpreted that “it is impermissible to speak of absolute time, simply because absolute time cannot be observed” means that since it is not observed, it doesn’t exist. That would lead to the conclusion that “time is relative”.
The interpretation I lean toward is that Heisenberg and Einstein recognized, just as Newton had, there is both absolute and relative time, not just one or the other. They simply claimed absolute time was unobservable and not relevant to physics. Which would be different than saying it didn’t exist.
The idea that time can be only relative, or only absolute, seems to be a late 20th century invention, used to emphasize how revolutionary Einstein’s relativity was. A consequence of this is that we’re presented with a false dilemma, we have to choose between time being one way or the other.
For Newton and Einstein, I do not think this dilemma was present, and both would be comfortable with absolute time and relative time each existing in their own ways.
The disagreement among them would have been that Newton felt his physics described absolute time and space, while Einstein would have asserted that his physics describe the world of relative time and space.
Everett
In the case where the mathematics of a theory only allows for one type of time, then there is a valid reason to choose one. And since relative time is what is actually observed, and it is desirable for theories to describe what is actually observed, then relative time is the best choice.
But what about a physical theory whose mathematics allow for two types of time? Due to our modern intuition to accept the false dilemma between absolute and relative time, it might be difficult to identify such a theory.
Hugh Everett may be best known for the “Many Worlds Interpretation of Quantum Mechanics”, but the real story behind that is over simplified as well.
Everett wrote a very lengthy thesis called “The Universal Wavefunction”. It was far too long to be a PhD thesis, so he wrote a shorter thesis, with many of the same ideas, known as “The Relative State Formulation of Quantum Mechanics”.
The first thesis was later read by Bryce DeWitt, who interpreted the work as suggesting parallel realities, and named it the “Many Worlds Interpretation”.
But it is Everett’s relative state formulation that is the most relevant to a discussion about absolute and relative time. Proposed as both a way to go about solving the problem of quantum gravity, and as a solution to the measurement problem, the ambitious Everett went so far as to name his work a “formulation” rather than an “interpretation” of quantum mechanics.
His solution to the measurement problem is to essentially flip it upside down. Rather than ask “what is the role of measurement in the model”, Everett says it is our task to model a measurement being made. He writes on page 9
What Everett is describing here could use an updated example, using modern technology.
Consider a computer running a physics engine. We’ll call this computer A, and it has its memory, which we’ll call memory A.
The physics engine models subatomic particles, like electrons and quarks, and also photons and other force carriers. With just those basic building blocks, It can model liquids, and solids, and gases. The basic particles can make up elements and molecules, and macroscopic objects like billiard balls and clouds. They should be even to make all the components of another computer, or a smartphone. Let’s call that computer B.
A smartphone fits Everett’s criteria for an observer: automatically functioning machines, possessing sensory apparatus and coupled to recording devices capable of registering past sensory data and machine configurations.
If computer B has a camera and is loaded with the proper software, it could examine its environment, and record measurements of things around it relative to each other. These measurements could be recorded in computer B’s memory, which is called memory B.
So now we have memory A, which contains the properties of subatomic particles that make a variety of objects, one of which is an observer whose memory B contains results of its measurements of the other objects.
Memory A and memory B both describe the virtual world, but from two different perspectives. Memory A is how it looks from the outside, and memory B is how it looks from the inside.
Considering such a theory, it’s difficult not to think back to Newton’s original definitions of time:
It seems to me you can draw a line between Newton’s definitions of absolute and relative time to Everett’s relative state formulation.
Conclusion
The story that Newton said “absolute!” and Einstein said “relative!” is useful, illustrative, and mostly true, in the context of what the math describes. But in the bigger picture, and with potentially new mathematical models with new abilities, it should be kept in mind that thinking about time as being only absolute or only relative is a false dilemma that Newton and Einstein would have considered as unnecessary as choosing only one side of a coin to exist. For there to be an “up” but not a “down”.
But I would like to show you that this story is not the whole truth.
Newton
Let’s start with Newton, who has this to say, on page 6 of the Principia:
Quote:
|
I do not define time, space, place, and motion, as being well known to all. Only I must observe, that the common people conceive those quantities under no other notions but from the relation they bear to sensible objects. |
He continues:
Quote:
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And thence arise certain prejudices, for the removing of which it will be convenient to distinguish them into absolute and relative, true and apparent, mathematical and common. I. Absolute, true, and mathematical time, of itself, and from its own nature, flows equably without relation to anything external, and by another name is called duration: relative, apparent, and common time, is some sensible and external (whether accurate or unequable) measure of duration by the means of motion, which is commonly used instead of true time; such as an hour, a day, a month, a year. II. Absolute space, in its own nature, without relation to anything external, remains always similar and immovable. Relative space is some movable dimension or measure of the absolute spaces; which our senses determine by its position to bodies; and which is commonly taken for immovable space |
While it can be debated what he meant precisely, it should be clear that simplifying his position to “time is absolute” does not tell the whole story.
I posted parts of the above quote by Newton in a tweet to Ethan Siegel and this was his response:
This is not meant to be a criticism of Dr. Siegel, who is kind enough to reply, just to illustrate how persistent this story is.
We can see that in Newton’s work, right on page 6, he explicitly defines what he means by space and time. There is nothing tacit about it. But these words rang a bell.
Einstein
We find in the book Relativity, by Einstein, page 32, the following:
Quote:
|
Now before the advent of the theory of relativity it had always tacitly been assumed in physics that the statement of time had an absolute significance, i.e. that it is independent of the state of motion of the body of reference. But we have just seen that this assumption is incompatible with the most natural definition of simultaneity; if we discard this assumption, then the conflict between the law of the propagation of light in vacuo and the principle of relativity (developed in Section VII) disappears. |
It appears from the quotation by Einstein that he is in fact claiming time to be relative, and only relative. That is a fair impression to get from this quote, and it seems that even Einstein’s contemporaries would have gotten a similar impression.
Here is Heisenberg’s account of a discussion with Einstein:
Quote:
|
“But you don't seriously believe," Einstein protested, "that none but observable magnitudes must go into a physical theory?" "Isn't that precisely what you have done with relativity?" I asked in some surprise. "After all, you did stress the fact that it is impermissible to speak of absolute time, simply because absolute time cannot be observed; that only clock readings, be it in the moving reference system or the system at rest, are relevant to the determination of time." "Possibly I did use this kind of reasoning," Einstein admitted, "but it is nonsense all the same. Perhaps I could put it more diplomatically by saying that it may be heuristically useful to keep in mind what one has actually observed. But on principle, it is quite wrong to try founding a theory on observable magnitudes alone. In reality, the very opposite happens. It is the theory which decides what we can observe." (In Physics and Beyond - Encounters and Conversations, Harper Torchbooks, 1972, p. 63.) |
The interpretation I lean toward is that Heisenberg and Einstein recognized, just as Newton had, there is both absolute and relative time, not just one or the other. They simply claimed absolute time was unobservable and not relevant to physics. Which would be different than saying it didn’t exist.
The idea that time can be only relative, or only absolute, seems to be a late 20th century invention, used to emphasize how revolutionary Einstein’s relativity was. A consequence of this is that we’re presented with a false dilemma, we have to choose between time being one way or the other.
For Newton and Einstein, I do not think this dilemma was present, and both would be comfortable with absolute time and relative time each existing in their own ways.
The disagreement among them would have been that Newton felt his physics described absolute time and space, while Einstein would have asserted that his physics describe the world of relative time and space.
Everett
In the case where the mathematics of a theory only allows for one type of time, then there is a valid reason to choose one. And since relative time is what is actually observed, and it is desirable for theories to describe what is actually observed, then relative time is the best choice.
But what about a physical theory whose mathematics allow for two types of time? Due to our modern intuition to accept the false dilemma between absolute and relative time, it might be difficult to identify such a theory.
Hugh Everett may be best known for the “Many Worlds Interpretation of Quantum Mechanics”, but the real story behind that is over simplified as well.
Everett wrote a very lengthy thesis called “The Universal Wavefunction”. It was far too long to be a PhD thesis, so he wrote a shorter thesis, with many of the same ideas, known as “The Relative State Formulation of Quantum Mechanics”.
The first thesis was later read by Bryce DeWitt, who interpreted the work as suggesting parallel realities, and named it the “Many Worlds Interpretation”.
But it is Everett’s relative state formulation that is the most relevant to a discussion about absolute and relative time. Proposed as both a way to go about solving the problem of quantum gravity, and as a solution to the measurement problem, the ambitious Everett went so far as to name his work a “formulation” rather than an “interpretation” of quantum mechanics.
His solution to the measurement problem is to essentially flip it upside down. Rather than ask “what is the role of measurement in the model”, Everett says it is our task to model a measurement being made. He writes on page 9
Quote:
|
We have the task of making deductions about the appearance of phenomena to observers which are considered as purely physical systems and are treated within the theory. To accomplish this it is necessary to identify some present properties of such an observer with features of the past experience of the observer. Thus, in order to say that an observer 0 has observed the event α, it is necessary that the state of 0 has become changed from its former state to a new state which is dependent upon α. It will suffice for our purposes to consider the observers to possess memo- ries (i.e., parts of a relatively permanent nature whose states are in correspon- dence with past experience of the observers). In order to make deductions about the past experience of an observer it is sufficient to deduce the present contents of the memory as it appears within the mathematical model. As models for observers we can, if we wish, consider automatically func- tioning machines, possessing sensory apparatus and coupled to recording devices capable of registering past sensory data and machine configurations. We can further suppose that the machine is so constructed that its present actions shall be determined not only by its present sensory data, but by the contents of its memory as well. Such a machine will then be capable of performing a sequence of observations (measurements), and furthermore of deciding upon its future experiments on the basis of past results. If we consider that current sensory data, as well as machine configuration, is im- mediately recorded in the memory, then the actions of the machine at a given instant can be regarded as a function of the memory contents only, and all relavant [sic] experience of the machine is contained in the memory. For such machines we are justified in using such phrases as “the machine has perceived A” or “the machine is aware of A” if the occurrence of A is represented in the memory, since the future behavior of the machine will be based upon the occurrence of A. In fact, all of the customary language of subjective experience is quite applicable to such machines, and forms the most natural and useful mode of expression when dealing with their behavior, as is well known to individuals who work with complex automata. |
Consider a computer running a physics engine. We’ll call this computer A, and it has its memory, which we’ll call memory A.
The physics engine models subatomic particles, like electrons and quarks, and also photons and other force carriers. With just those basic building blocks, It can model liquids, and solids, and gases. The basic particles can make up elements and molecules, and macroscopic objects like billiard balls and clouds. They should be even to make all the components of another computer, or a smartphone. Let’s call that computer B.
A smartphone fits Everett’s criteria for an observer: automatically functioning machines, possessing sensory apparatus and coupled to recording devices capable of registering past sensory data and machine configurations.
If computer B has a camera and is loaded with the proper software, it could examine its environment, and record measurements of things around it relative to each other. These measurements could be recorded in computer B’s memory, which is called memory B.
So now we have memory A, which contains the properties of subatomic particles that make a variety of objects, one of which is an observer whose memory B contains results of its measurements of the other objects.
Memory A and memory B both describe the virtual world, but from two different perspectives. Memory A is how it looks from the outside, and memory B is how it looks from the inside.
Considering such a theory, it’s difficult not to think back to Newton’s original definitions of time:
Quote:
|
Absolute, true, and mathematical time, of itself, and from its own nature, flows equably without relation to anything external, and by another name is called duration: relative, apparent, and common time, is some sensible and external (whether accurate or unequable) measure of duration by the means of motion |
Conclusion
The story that Newton said “absolute!” and Einstein said “relative!” is useful, illustrative, and mostly true, in the context of what the math describes. But in the bigger picture, and with potentially new mathematical models with new abilities, it should be kept in mind that thinking about time as being only absolute or only relative is a false dilemma that Newton and Einstein would have considered as unnecessary as choosing only one side of a coin to exist. For there to be an “up” but not a “down”.
via International Skeptics Forum https://ift.tt/3xrVPCz
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