What is the Fabric of Spacetime Made Of?

[JesseM]

Stop with this run around. Is a rock a physical thing according to science? Yes/No

Is light a physical thing according to science?

Science has defined itself and it's definitions.

I think most physicists would say that physics is basically just about coming up with mathematical models which are used to make accurate predictions about experimental results, I challenge you to point to any physics textbooks that define terms like "real" or "physical thing".

Are some of you on this thread just kids unfamiliar with physics and you are just here having fun?

I can not understand how some of you can say the things that you do if you had any basic understanding of science.

The same question might be asked of you, since the only sources you cite tend to be sources like dictionaries instead of scientific papers or textbooks. Have you ever taken any actual courses in physics, for example? You've shown in previous comments that you aren't familiar with some very basic ideas in classical mechanics, like the frame-dependence of energy (similarly, on this thread you pooh-poohed DaleSpam's definition of energy as force times distance by citing a dictionary which defined energy as 'capacity to do work', not realizing that 'work' is a technical term in physics meaning...force times distance!) Your dismissive, mocking attitude towards people who pretty clearly know the fundamentals of the subject a lot better than you reminds me of the psychological phenomenon discussed here where the people who know the least about a subject tend to have the most inflated self-assessments about their ability to evaluate claims related to the subject, because their own ignorance prevents them from realizing how little they actually know about it in comparison to others.

Science has defined what is real. This talk of philosophy is just an avoidance of my initial question. Look up the term real in a dictionary, that is what I mean by real.

Case in point. If you were more familiar with actual scientific literature like textbooks and papers, you'd probably notice that scientists almost never use a word like "real" (at least not in a physics context) because they realize how difficult it is to come up with a rigorous definition. For example, are forces "real"? They're certainly useful in Newtonian mechanics, but then you find that in other theories like quantum physics and general relativity the notion of forces is no longer used, and yet the different theories make nearly identical quantitative predictions in a range of circumstances. As I said, the essence of physics as seen by most physicists is just coming up with abstract mathematical models (as opposed to mechanical models that can be grasped conceptually in terms of 'real' entities and how they interact) that make accurate quantitative predictions. Consider the following discussion by Richard Feynman (in his book The Character of Physical Law), one of the great physicists of the 20th century:

On the other hand, take Newton's law for gravitation, which has the aspects I discussed last time. I gave you the equation:

F=Gmm'/r^2

just to impress you with the speed with which mathematical symbols can convey information. I said that the force was proportional to the product of the masses of two objects, and inversely as the square of the distance between them, and also that bodies react to forces by changing their speeds, or changing their motions, in the direction of the force by amounts proportional to the force and inversely proportional to their masses. Those are words all right, and I did not necessarily have to write the equation. Nevertheless it is kind of mathematical, and we wonder how this can be a fundamental law. What does the planet do? Does it look at the sun, see how far away it is, and decide to calculate on its internal adding machine the inverse of the square of the distance, which tells it how much to move? This is certainly no explanation of the machinery of gravitation! You might want to look further, and various people have tried to look further. Newton was originally asked about his theory--'But it doesn't mean anything--it doesn't tell us anything'. He said, 'It tells you how it moves. That should be enough. I have told you how it moves, not why.' But people are often unsatisfied without a mechanism, and I would like to describe one theory which has been invented, among others, of the type you migh want. This theory suggests that this effect is the result of large numbers of actions, which would explain why it is mathematical.

Suppose that in the world everywhere there are a lot of particles, flying through us at very high speed. They come equally in all directions--just shooting by--and once in a while they hit us in a bombardment. We, and the sun, are practically transparent for them, practically but not completely, and some of them hit. ... If the sun were not there, particles would be bombarding the Earth from all sides, giving little impuleses by the rattle, bang, bang of the few that hit. This will not shake the Earth in any particular direction, because there are as many coming from one side as from the other, from top as from bottom. However, when the sun is there the particles which are coming from that direction are partially absorbed by the sun, because some of them hit the sun and do not go through. Therefore the number coming from the sun's direction towards the Earth is less than the number coming from the other sides, because they meet an obstacle, the sun. It is easy to see that the farther the sun is away, of all the possible directions in which particles can come, a smaller proportion of the particles are being taken out. The sun will appear smaller--in fact inversely as the square of the distance. Therefore there will be an impulse on the Earth towards the sun that varies inversely as the square of the distance. And this will be the result of a large number of very simple operations, just hits, one after the other, from all directions. Therefore the strangeness of the mathematical relation will be very much reduced, because the fundamental operation is much simpler than calculating the inverse of the square of the distance. This design, with the particles bouncing, does the calculation.

The only trouble with this scheme is that it does not work, for other reasons. Every theory that you make up has to be analysed against all possible consequences, to see if it predicts anything else. And this does predict something else. If the Earth is moving, more particles will hit it from in front than from behind. (If you are running in the rain, more rain hits you in the front of the face than in the back of the head, because you are running into the rain.) So, if the Earth is moving it is running into the particles coming towards it and away from the ones that are chasing it from behind. So more particles will hit it from the front than from the back, and there will be a force opposing any motion. This force would slow the Earth up in its orbit, and it certainly would not have lasted the three of four billion years (at least) that it has been going around the sun. So that is the end of that theory. 'Well,' you say, 'it was a good one, and I got rid of the mathematics for a while. Maybe I could invent a better one.' Maybe you can, because nobody knows the ultimate. But up to today, from the time of Newton, no one has invented another theoretical description of the mathematical machinery behind this law which does not either say the same thing over again, or make the mathematics harder, or predict some wrong phenomena. So there is no model of the theory of gravity today, other than the mathematical form.

If this were the only law of this character it would be interesting and rather annoying. But what turns out to be true is that the more we investigate, the more laws we find, and the deeper we penetrate nature, the more this disease persists. Every one of our laws is a purely mathematical statement in rather complex and abstruse mathematics.

...[A] question is whether, when trying to guess new laws, we should use seat-of-the-pants feelings and philosophical principles--'I don't like the minimum principle', or 'I do like the minimum principle', 'I don't like action at a distance', or 'I do like action at a distance'. To what extent do models help? It is interesting that very often models do help, and most physics teachers try to teach how to use models and to get a good physical feel for how things are going to work out. But it always turns out that the greatest discoveries abstract away from the model and the model never does any good. Maxwell's discovery of electrodynamics was made with a lot of imaginary wheels and idlers in space. But when you get rid of all the idlers and things in space the thing is O.K. Dirac discovered the correct laws for relativity quantum mechanics simply by guessing the equation. The method of guessing the equation seems to be a pretty effective way of guessing new laws. This shows again that mathematics is a deep way of expressing nature, and any attempt to express nature in philosophical principles, or in seat-of-the-pants mechanical feelings, is not an efficient way.

It always bothers me that, according to the laws as we understand them today, it takes a computing machine an infinite number of logical operations to figure out what goes on in no matter how tiny a region of space, and no matter how tiny a region of time. How can all that be going on in that tiny space? Why should it take an infinite amount of logic to figure out what one tiny piece of space/time is going to do? So I have often made the hypothesis that ultimately physics will not require a mathematical statement, that in the end the machinery will be revealed, and the laws will turn out to be simple, like the chequer board with all its apparent complexities. But this speculation is of the same nature as those other people make--'I like it', 'I don't like it',--and it is not good to be too prejudiced about these things.

 

[p764rds]

I think most physicists would say that physics is basically just about coming up with mathematical models which are used to make accurate predictions about experimental results, I challenge you to point to any physics textbooks that define terms like "real" or "physical thing".

Back in the Quantum Physics section of this board a couple of people are heavily pushing Bohm Theory to bring back 'classical physics' and 'reality' ontology - by using the concept of pilot waves that travel FTL. The idea is that information from the 'effect' travels back in time to the cause using a 'reference frame' - weak causality is apparently OK provided it is valid from 'quantum preparation' to observation only. Then quantum bizarreness 'goes away'.


Thats why a lot of contributors are arguing (against) the 'real and physical' concept. So there is a debate at present revolving around 'real and physical' in the Quantum Physics section. (I am only in this section looking for good evidence against 'physicality of 3 dimensional space' for a couple of paragraphs of writing I am doing)

 

[JesseM]

Back in the Quantum Physics section of this board a couple of people are heavily pushing Bohm Theory to bring back 'classical physics' and 'reality' ontology - by using the concept of pilot waves that travel FTL. The idea is that information from the 'effect' travels back in time to the cause using a 'reference frame' - weak causality is apparently OK provided it is valid from 'quantum preparation' to observation only. Then quantum bizarreness 'goes away'.


Thats why a lot of contributors are arguing (against) the 'real and physical' concept. So there is a debate at present revolving around 'real and physical' in the Quantum Physics section. (I am only in this section looking for good evidence against 'physicality of 3 dimensional space' for a couple of paragraphs of writing I am doing)

The different "interpretations" of QM help back up the case Feynman makes in this paragraph of the longer quote I posted above:

It is interesting that very often models do help, and most physics teachers try to teach how to use models and to get a good physical feel for how things are going to work out. But it always turns out that the greatest discoveries abstract away from the model and the model never does any good. Maxwell's discovery of electrodynamics was made with a lot of imaginary wheels and idlers in space. But when you get rid of all the idlers and things in space the thing is O.K. Dirac discovered the correct laws for relativity quantum mechanics simply by guessing the equation. The method of guessing the equation seems to be a pretty effective way of guessing new laws. This shows again that mathematics is a deep way of expressing nature, and any attempt to express nature in philosophical principles, or in seat-of-the-pants mechanical feelings, is not an efficient way.

Crucially, none of the "interpretations" of QM actually makes any distinct predictions about experimental results. As he says, people's interpretations may help them get a "good physical feel" for QM, and as a philosophical matter it may even be that some interpretation really is a better reflection of "reality" than the others, but as far as actually making predictions you can get rid of all the "wheels and idlers" specific to a given interpretation (like the 'pilot wave' of Bohmian mechanics) and it makes no difference, all interpretations are equally useless in terms of making novel predictions, nor is there a shred of physical evidence that supports one interpretation over any other.

 

[john 8]

I think most physicists would say that physics is basically just about coming up with mathematical models which are used to make accurate predictions about experimental results, I challenge you to point to any physics textbooks that define terms like "real" or "physical thing".

The same question might be asked of you, since the only sources you cite tend to be sources like dictionaries instead of scientific papers or textbooks. Have you ever taken any actual courses in physics, for example? You've shown in previous comments that you aren't familiar with some very basic ideas in classical mechanics, like the frame-dependence of energy (similarly, on this thread you pooh-poohed DaleSpam's definition of energy as force times distance by citing a dictionary which defined energy as 'capacity to do work', not realizing that 'work' is a technical term in physics meaning...force times distance!) Your dismissive, mocking attitude towards people who pretty clearly know the fundamentals of the subject a lot better than you reminds me of the psychological phenomenon discussed here where the people who know the least about a subject tend to have the most inflated self-assessments about their ability to evaluate claims related to the subject, because their own ignorance prevents them from realizing how little they actually know about it in comparison to others.

Case in point. If you were more familiar with actual scientific literature like textbooks and papers, you'd probably notice that scientists almost never use a word like "real" (at least not in a physics context) because they realize how difficult it is to come up with a rigorous definition. For example, are forces "real"? They're certainly useful in Newtonian mechanics, but then you find that in other theories like quantum physics and general relativity the notion of forces is no longer used, and yet the different theories make nearly identical quantitative predictions in a range of circumstances. As I said, the essence of physics as seen by most physicists is just coming up with abstract mathematical models (as opposed to mechanical models that can be grasped conceptually in terms of 'real' entities and how they interact) that make accurate quantitative predictions. Consider the following discussion by Richard Feynman (in his book The Character of Physical Law), one of the great physicists of the 20th century:

I like you. You have made some interesting statements, something that contribues to the thread. You are articulate, and your communication is your own.

I think you said something about my antagonistic tone on this thread, your right, I will watch it.

You have mentioned many things that I would like to respond to, but it is getting late so I will have to respond later.

 

[p764rds]

You are completely wrong! You consider that the computer in front of you exists. When you go to the store to buy food, you are putting real physical things in your basket, not math equations. If someone were to ask you to pass the salt, you would grab the physical object and move it in a direction toward that person. You did all of this without using math to prove the existence of anything. You and I agree that we are breathing the substance known as air. I knew that this substance was real and existed before I understood math.

I read this on the Internet, I am not saying I agree, but I cannot think of anything you would agree with less...

"Its my view that you are made of data (numbers) and me too, and space, mass and energy -all numbers. We are all next to each other in a giant river of numbers in information space behind space-time. There is nothing that is not at heart a number. Data has no mass or spatial size and can implement the mathematics and logic required to run a Universe such as this one from information space. Data and time share a common basis. Leibnitz and Plato would probably agree."

 

[JesseM]

I like you. You have made some interesting statements, something that contribues to the thread. You are articulate, and your communication is your own.

I think you said something about my antagonistic tone on this thread, your right, I will watch it.

You have mentioned many things that I would like to respond to, but it is getting late so I will have to respond later.

Thanks, I'm glad you didn't take my comments the wrong way, I'm critical of some of your main ideas and the dismissive way you often respond to opposing arguments, but I don't mean anything personal by this criticism. Take your time in thinking about my comments and responding.

 

[Saw]

Since I am quite fond of the subject, I’ve thought I should share some opinions:

I agree with John8 that time, space (and even motion, I would add) are just mind-made concepts, intellectual tools and they do not have physical existence.

I also agree with him that what does have physical existence is reality: some “actors” (let us call them like that in want of a better term) and their interactions.

Unfortunately, the features of the “actors” do not jump directly into your mind. You have to measure them. Measurement in turn is like organizing a competition between the actors and some other small actors (also real things) that you take as reference (let us call them the miniatures). Thus you can say that a number of the miniatures “are”, for the relevant purpose, the actor, because the former perfectly mirror or reflects the latter.

I would propose this metaphor: the height of a beautiful princess is measured against and found equal to the height of three ugly dwarves standing one on top of the other; once this is done, we can use the dwarves to check if a wedding dress is too long or too short for the princess; after that, the three dwarves escape and walk around mimicking the feminine gestures of the princess, pretending that they “are” the princess. Well, this is somehow true, as long as we do not forget that it is so for certain limited purpose (like checking if a dress will be too short or too long for the princess), but it is not for other purposes: if you are the prince of the tale, you would not like to marry the dwarves, even if you are a scientist, just because it has been “objectively measured” that the dwarves, if put one on top of the other, are as tall as the princess; likewise, you would not like to marry the dwarves, even if you are a mathematician, just because an equation states that 1 princess = 1 dwarf times 3. You would remember that the physical and mathematical “concept” that the dwarves mirror the princess is only valid for the purpose for which it was invented.

Thus I agree with most posters that concepts (like time) are to the essence of physic. That is the nature of things. Since we are ourselves physical things, we cannot try to ascertain what things are and what happens inside things without choosing a reference for comparison and talking “as if” the reference were the measured object. This is so true that, in fact, if you try to define reality in terms other than comparisons with other realities, you are doomed to failure. I myself in another thread have used the terms “particle or wave” as meaning the ultimate “building blocks” of reality. However, one can do this in order to make the argument that reality is something different from concepts, but cannot do so without admitting that “particles” or “waves” are themselves also concepts.

I also agree with other posters that physics is what is (it has reached an astonishing level of development) because it has waived the ambition to explain things in terms of what they intrinsically are and contented itself with the comparisons = competitions = observations = measurements = concepts, which are arranged in mathematical equations. The example of the Law of Universal Gravitation is very well brought and Newton’s assertion “I frame no hypothesis” as to why the formula is correct a good slogan of the trick.

But it must also be said that the formula in itself is a hypothesis that seeks a more fundamental explanation than previous formulations. Galileo’s formulas related to gravitation only dealt with the concepts (“mirrors”) of distance and time. Newton was bolder and made a hypothesis about why objects traverse certain distances in certain time lapses: there is an interaction between two masses and the strength of the interaction has to do with the quantity of mass of the objects involved in the interaction. That was a big progress and in fact, having this in mind enabled Newton to and guided him in his correction and improvement of Kepler’s laws, which were based on observations leaning exclusively on time and distance. Of course, mass itself is also a concept you measure in “competitions” between masses, but a concept that better mirrors what really happens in reality and thus a more powerful one.

Conclusions: yes, concepts are the essence of physics, but it is not out of question to remember from time to time that they are so, mere mirrors of reality that do their job only to the extent that we use them in accordance with their intrinsic logic. In particular, I don’t think it would be inappropriate to mention so in the prologue of physics textbooks…

 

[Dale]

Lets see here, you say time is not a wave. then you go to give a definition of a wave and say that time is part of this definition of a wave. O.K. Pause; I want to give you time to think about what you said.

Go ahead, I will allow you to really think about what you just said.

Maybe you should have a cup of coffee and go for a walk, clear your head.

Your rebuttal is not logical. Here is an analogy: a radio transmitter is not a cell phone. A cell phone is defined as a radio reciever and transmitter that interface with a cell tower and the phone system. A radio transmitter is not a cell phone even though a radio transmitter is an essential part of the definition of a cell phone.

Similarly time is not a wave, but time is an essential part of the definition of a wave.

You have now asked me to give my definition of a wave.

And you have avoided giving your definition yet again. This argument has been entirely semantic up to this point, so clearly defining your terms is essential. We cannot progress unless we each understand what the other means by these important terms. So I ask again, what are your definitions of "wave" and "energy"? I have given the standard physics definitions of "wave" and "energy", which are the definitions I use. Can you not do the same?

 

[Naty1]

Most people, fortunately, post questions and issues to gain an under standing from the point of view of best experimental and theoretical physics...Other just post to argue with such responses...it's clear who is who and the latter are neither worth the time nor will they learn if given the time...

 

[A.T.]

You have now asked me to give my definition of a wave.

I have given the standard physics definitions of "wave" and "energy", which are the definitions I use. Can you not do the same?

No, because he is using the definitions provided to him by "science". But which "science" might it be? Gender studies? Ornithology? Wait! He is invoking "science" & "logic". Maybe Scientology?

He's obvously http://www.youtube.com/watch?v=2IlHgbOWj4o".

 

[p764rds]

Gravity bends space, space-time is a math model only.

If space-time is a math model only, then it means that objects are all on top of each other and that the metrics ("space") are only parameters attached to objects that identify them uniquely from other objects. (or am I way out here?)

Is flat (no gravity) euclidean space possible at all outside of mathematics? (I don't mean by nesting it in another space). My opinion is that flat space is not possible outside mathematics- but I am not 100% sure. Someone told me the question has no meaning and is vacuous (no pun intended) because I need an object in the space - what's that all about?