Jump to content
Objectivism Online Forum

Rate this topic

Recommended Posts

I am surprised there are so few posts on Physics here. Perhaps I can find someone who is interested in this topic.

If we assume Peikoff's proof is correct and existence is a PLENUM, then what lies outside the Big Bang area, which has a radius of about 14 billion light years?

Something is out there, (in other words, "existence") ... which implies that all of existence did NOT take part in the explosion known as the Big bang.

Since existence is a PLENUM, then for all intents and purposes, existence is "infinite," and reality continues as we pass the debris zone of the Big Bang.

Of course, this external mass-energy (outside of the debris zone of the big bang explosion) must exert a gravitational force on the expanding Big Bang material.

If we assume the theory that this external mass-energy is responsible for the accelerated expansion of the Big Bang debris, what does this imply about how this external mass-energy is distributed? This distribution would be a PREDICTION of this theory (for the person who wants to work it out). I would love to see what it predicts.

Does it predict the fractal distribution from the November 2011 paper by Carati:

http://arxiv.org/pdf/1111.5793v1.pdf

(or http://phys.org/news/2011-12-dark.html)

If so, since this paper is basically an alternative theory to Dark Matter, we would hence have a connection between Dark Matter and Dark Energy:

Both concepts can be explained instead by the mass-energy that lies outside the small debris zone of the Big Bang explosion.

So in this (qualitative) theory or approach, perhaps Dark Matter is not needed. What contributes the additional gravitational field structure that leads to galactic motion is external non-big bang mass and energy. And Dark Energy is not needed: only if the Big Bang were occurring in otherwise empty space would you think that the expansion would have to be slowing down.

More later

thanks

Share this post


Link to post
Share on other sites

A few points to consider:

(1) The Big Bang was not an explosion

(2) There is no "outside" the Big Bang "area"

(3) The observable universe is not the extent of the Big Bang "area"

(4) The "debris" of the Big Bang is all that there is; there's no "pass(ing) the debris zone"

(5) Gravity isn't a force

(6) The metric expansion of space is not an expansion of a "material" or of a "debris".

Edited by Alfred Centauri

Share this post


Link to post
Share on other sites

I am surprised there are so few posts on Physics here. Perhaps I can find someone who is interested in this topic.

If we assume Peikoff's proof is correct and existence is a PLENUM,

...

Since existence is a PLENUM, then for all intents and purposes, existence is "infinite," and reality continues as we pass the debris zone of the Big Bang.

Can you provide the full Peikoff quote please? I remember Rand saying something about this in ItOE, but not Peikoff.

A common definition of plenum is "a space or all space every part of which is full of matter." I take issue with this definition, because it assumes space can exist without matter. After reading Einstein's Relativity, I believe that space has no existence independent of matter. It is merely a relationship between entities. Reality is background-independent. Space as a background functions to make predictions in Newtonian physics, but it is not reality.

Say you have four particles oriented at the vertices of a tetrahedron and nothing else - that's your universe. Some would say that the space in the middle of that tetrahedron is empty. I would say there is nothing in the middle of those particles (neither matter nor space). Space in this scenario is the collection of relationships between each particle with every other particle (i.e. the 6 edges of the tetrahedron).

Nothing is infinite, and the fact that you arrived at such a conclusion should have made you rethink your process.

What I think is meant when Objectivists say the universe is a plenum is simply that nothing cannot exist - there is no such thing as "empty" space. But this should not be taken as an impetus for positing something which fills a space incorrectly assumed to be there. This leads to infinite regresses where you decide that if there are two points, A and B, that there must be some point between them A', and some point between A and A', A'', etc.

Share this post


Link to post
Share on other sites

Can you provide the full Peikoff quote please? I remember Rand saying something about this in ItOE, but not Peikoff.

A common definition of plenum is "a space or all space every part of which is full of matter." I take issue with this definition, because it assumes space can exist without matter. After reading Einstein's Relativity, I believe that space has no existence independent of matter. It is merely a relationship between entities. Reality is background-independent. Space as a background functions to make predictions in Newtonian physics, but it is not reality.

Say you have four particles oriented at the vertices of a tetrahedron and nothing else - that's your universe. Some would say that the space in the middle of that tetrahedron is empty. I would say there is nothing in the middle of those particles (neither matter nor space). Space in this scenario is the collection of relationships between each particle with every other particle (i.e. the 6 edges of the tetrahedron).

Nothing is infinite, and the fact that you arrived at such a conclusion should have made you rethink your process.

What I think is meant when Objectivists say the universe is a plenum is simply that nothing cannot exist - there is no such thing as "empty" space. But this should not be taken as an impetus for positing something which fills a space incorrectly assumed to be there. This leads to infinite regresses where you decide that if there are two points, A and B, that there must be some point between them A', and some point between A and A', A'', etc.

From the position of someone who knows little to nothing about physics: does this mean that if a being were to move in one direction for eternity that he would eventually end up back where he started? Or if nothing is infinite, does this mean that time itself will end?

Share this post


Link to post
Share on other sites

Location, motion, and any other concept dealing with space or measurement of distances only has meaning as a relationship between two (or more) entities.

In the case of your being moving in one direction, you must ask: "In one direction relative to what?" If the whole universe were just one entity, that entity couldn't be said to be moving. Your question depends on aspects of the universe such at matter/energy density, etc. Last time I heard a talk about it (>15 years ago), physicists were leaning towards space having an overall positive curvature and that it is finite, but unbounded. This means space is similar to the surface of a sphere or torus, you can move indefinitely in one direction, but it is limited in size.

If you look at a simple case of two particles moving steadily away from each other, I would say that space grows as the particles separate. The distance between the particles, in this case, is space. There is no space "out there" waiting to be filled with a particle.

Share this post


Link to post
Share on other sites

What I think is meant when Objectivists say the universe is a plenum is simply that nothing cannot exist - there is no such thing as "empty" space. But this should not be taken as an impetus for positing something which fills a space incorrectly assumed to be there. This leads to infinite regresses where you decide that if there are two points, A and B, that there must be some point between them A', and some point between A and A', A'', etc.

There are no fundamental particles, there are only fundamental quantum fields. There is no empty space because all is suffused with multiple fields. Some of the fields due to their symmetry are mathematically equivalent to point particles in some contexts, for example electrons, but other contexts make those same particles behave in a way only explainable by a field analysis and the wave equation solution. The field analysis is more general in that a particle can be treated as an excitation of an underlying field but there is no way to get a field out of a particle.

Your infinite regress objection fails because the infinite points are each massless, chargeless, spinless, (everything-less) dimensionless mathematical constructs that do not actually exist so there is no contradiction created, an infinite amount of nothings are still nothing.

This topic is philosophically important because the idea that there are fundamental particles that are the only thing that really exists and so the only thing that can truly be a cause and that everything else is composed of them is metaphysically poisonous in that it leads straight to reductive determinism. I take this opportunity to once again publicize the paper Physicalism, Emergence, and Downward Causation by Campbell and Bickhard.

Share this post


Link to post
Share on other sites

"There are no fundamental particles, there are only fundamental quantum fields."

That's not quite right Grames. The quantum fields of QFT are operator valued fields. The field operators operate on states in a Fock space. It is the states that represent the particles, not the quantum field.

For reference: http://www.quantumfieldtheory.info/Chap01.pdf

When the word “field” is used classically, it refers to an entity, like fluid wave amplitude, E, or

B, that is spread out in space, i.e., has different values at different places. By that definition, the

wave function of ordinary QM, or even the particle state in QFT, is a field. But, it is important to

realize that in quantum terminology, the word “field” means an operator field, which is the solution

to the wave equations, and which creates and destroys particle states. States (= particles = wave

functions = kets) are not considered fields in that context.

So, in the context of QFT, there is definitely more than just quantum fields, there are also entities with states with representations in a very abstract space.

Edited by Alfred Centauri

Share this post


Link to post
Share on other sites

Thanks for that clarification of the ambiguous reference of the word "field". The classical usage of "field" is what I intended and even in the quote you provided "By that definition, the

wave function of ordinary QM, or even the particle state in QFT, is a field."

In doing some superficial background reading into learning what a Fock space is and what it represents I learned that it is not actually in one-to-one correspondence with a set of particles, which supports my point. Here is one philosophy paper that provides an overview of interpretation for QFT: Objects or Events? Towards an Ontology for Quantum Field Theory The author's 'causal net' criteria for identifying particulars is intuitively pleasing (to me anyway.)

Share this post


Link to post
Share on other sites

Thanks for the link Grames. And yes, your point that, according to QFT, "particles" are just quanta (discrete and indistinguishable mode excitations) of an underlying entity and are thus not fundamental is good. But again, keep in mind that the underlying entity "lives" in in a very abstract space.

The point I'm zeroing in on here is that while, in QFT, there is a field that is a function of the space and time coordinates, that field is a field of operators with no clear ontology. The entity that possesses states and for which there are quanta of excitations "lives" in a very abstract space.

This is related to the situation in QM where, when the system contains two or more particles, the wavefunction for the system "lives" in a higher dimensional space. For example, for a two particle system, the wavefunction is a function of 6 spatial coordinates (and time).

Since QFT is a theory of an unlimited number of "particles", the space has, loosely speaking, an unlimited number of coordinates.

On another note, on the Bohmian view, there are fundamental particles with definite positions and trajectories. I'm looking over this paper right now to review what a Bohmian QFT might look like.

Edited by Alfred Centauri

Share this post


Link to post
Share on other sites

Yes, the ontology of field operators is not clear. Taking the path integral approach seriously as the basis of an ontology may be more productive. Feynman's book QED was my introduction to that method, and the textbook you linked earlier has a chapter covering it at Path Integrals in Quantum Theories. The appeal of this theory is that the underlying existent treats all of the many paths the same without weighting the classical ones more heavily than paths that violate conservation of energy, the least distance principle, or what have you. The underlying existent does not somehow have built into it a priori knowledge of what it is supposed to do, rather much of what we recognize as laws of physics simply falls out of the constructive and destructive summation of all the paths.

The Bohmian ontology of particles plus guiding or "pilot" waves is a kind of field theory because it does not assert that only particles exist. In conceding Ψ also exists it also makes reductive determinism impossible to maintain. As far as I can tell Bohmian QM is also plausible and compatible with a rational philosophy.

Share this post


Link to post
Share on other sites

There are no fundamental particles...

I was not trying to assert that as the case. My point was, and remains, that in light of GR, space exists as a relationship between entities. It does not have an independent existence. The predictive success and relative completeness of QFT are certainly no reason to ignore the background-independence of GR (See the efforts of Smolin, et al.) There is no absolute space, so there are no absolute locations, positions, distances, speeds, etc.

Your infinite regress objection fails because the infinite points are each massless, chargeless, spinless, (everything-less) dimensionless mathematical constructs that do not actually exist so there is no contradiction created, an infinite amount of nothings are still nothing.

Point taken. (Pun intended.)

I take this opportunity to once again publicize the paper Physicalism, Emergence, and Downward Causation by Campbell and Bickhard.

Thanks for the link. It is a great paper.

Share this post


Link to post
Share on other sites

I will try one more post on this specific subject to see if anyone replies on topic:

I hope A. Carati et al (or other Astrophysicist) can one day modify their calculations with these mathematical assumptions:

(1) Keep the assumption that the distribution of the "far away galaxies" is unevenly fractal-like in nature, but:

(2) Our big bang is expanding into these far-away galaxies, 15 billion light years away and further and further out.

(3) These "external" galaxies are potentially infinite and (4) create a convergent gravitational field within our big bang area.

Then (4) adjust the fractal distribution in order to account for "dark matter" effects.

Then use this (preliminary) theory to predict what effect this will have on the rate of expansion of the big bang.

Then see if this predicted effect is equal to the observed accelerated expansion rate.

Then see if other predictions ensue, which can contain other and then other here-to-fore unexplained galactic phenomena.

--- more later ---

Share this post


Link to post
Share on other sites

I will try one more post on this specific subject to see if anyone replies on topic:

The replies have been as on-topic as possible given your hopelessly inadequate understanding of the background concepts. There is no "expanding into", and that is on the ordinary understanding of physics not an uniquely Objectivist one. See the Wikipedia article Metric Expansion of Space.

Share this post


Link to post
Share on other sites

Would you mind elaborating on this one a little for me?

Only a little? :)

OK, the short version. In the context of the General Theory of Relativity (GTR), gravity is the curvature of spacetime and not a force in spacetime. The world-line (path through spacetime) of objects in free-fall are geodesics of the spacetime; the path through spacetime of an unaccelerated object. This explains why, in free-fall, no weight is felt, i.e., we feel no acceleration, no force, no "gravity".

In the context of Newtonian gravity, there is inertial mass (resistance to acceleration) and gravitational mass (gravitational "charge", the source of the gravitational "force"). There is no reason for these two very different properties to be equal in Newtonian gravity but, observationally, they are.

GTR neatly solves this unlikely and unexplained coincidence.

Share this post


Link to post
Share on other sites

I think this sounds odd to me, for gravity to not be a force, because I've come across so many places where gravity is still referred to and treated as a force even while the curved spacetime idea of gravity is noted and treated as truth. I didn't realize there was any reason these were incompatible. Hmm . . .

If I'm understanding what you said about "world-lines" correctly, another way to put it would be that the path traveled by an object in free fall is the same as it would be if the object were not accelerating at all. Is this correct? It makes no sense for free fall to mean we aren't moving of course because then we'd only hit the ground if we jumped out of a plane if the Earth moved to us instead. That would clearly be preposterous. I assume acceleration here must mean going faster rather than not going at all -----

You know what? Could you just please expand upon those few sentences in the GTR paragraph a bit more? I'm just not seeing how those sentences connect, like there are holes in the explanation about how we got from point A to point E. Everything I come up with to try to put them together is just clearly wrong, I know that for sure. I'm not unfamiliar with the basic idea of spacetime and curving of it, but it starts to get foggier from there. I could understand something like "gravity is a push rather than a pull" with space and objects pressing on each other, but I don't think that's right because, well, nobody as far as I know has been saying anything about what substance space would be made of and furthermore, if space was pressing on us then we should get squashed if we were to open up space suits in space rather than kind of explode. Though on the latter point perhaps space could be more crunched together, denser, and therefore more forceful around objects thus pushing more in that area right around objects, the bigger the object the more space displaced et cetera, but even then that still leaves open the question of what substance space is made of among various other things that don't seem to add up . . . Bah!

Share this post


Link to post
Share on other sites

Grames would you feel like pointing out what part of the paper you posted here and elsewhere a while ago supports abandoning entity based causation most explicitly? I read through it a while ago but was reading three other things and was a bit distracted.

A lucid discussion really needs to be had about the ontological actuals of physics theory. That is, which existents are abstract objects and which are metaphysical particulars. This is the source of most confusion in physics today. It's common to see folks equivocate back and forth while discussing many mathematical terms and ending up with no clear ontology on what is being claimed physically.

Edited by Plasmatic

Share this post


Link to post
Share on other sites

I've come across so many places where gravity is still referred to and treated as a force

In the non-relativistic limit, gravity "looks" like a force so it's OK to consider it a force in most contexts. However, at cosmological scales, we leave the non-relativistic regime and, in that context, gravity is not a force.

If I'm understanding what you said about "world-lines" correctly, another way to put it would be that the path traveled by an object in free fall is the same as it would be if the object were not accelerating at all. Is this correct?

Understood properly, the above is correct. However, I suspect that you don't understand this properly.

First, let's be sure we understand "free-fall" in the context of GTR. An object in free-fall is free from any external force (and remember, gravity is not a force in the context of GTR). Between any two events (points) in spacetime, there are an infinity of possible world lines that include those events. One of those possible world lines is special in the following way: the elapsed time between the two events along that world line is larger than any other, i.e., that world line is the geodesic connecting the two events.

Originally, Einstein postulated that the world line of an object free from external force is a geodesic but it turned out that this actually follows from the equations of GTR. The world line of an object in free fall (free from external force) is a geodesic, i.e., path of largest elapsed time.

Second, let's be sure we understand acceleration in the context of GTR. In particular, the relativity of acceleration due to gravity. In the Special Theory of Relativity (STR), acceleration is absolute. If an inertial observer observes that the motion of an object changes with time, it is the object that is accelerating. When it comes to acceleration due to gravity, however, things are not so clear.

Imagine two spacecraft in deep space with an astronaut in each. Both astronauts observe that the relative motion between their spacecraft is changing with time. In one spacecraft, the astronaut observes that his accelerometers all read zero while the other astronaut observes that one of his accelerometers is non-zero and that his rocket engine is on. Within STR, we can say absolutely that the later astronaut's spacecraft is accelerating while the former astronaut's spacecraft is not accelerating.

But, in GTR, it is the case that the later astronaut can equivalently claim that his spacecraft is at rest in a uniform gravity field (by virtue of the fact that his engine is on and thrusting in the direction opposite that of the field) and that it is the other spacecraft that is accelerating under the influence of the gravity field.

So, back to your question:

another way to put it would be that the path traveled by an object in free fall is the same as it would be if the object were not accelerating at all. Is this correct?

If, by acceleration, you mean acceleration due to a force (and remember, gravity is not a force) then yes, you are correct. If, however, you mean acceleration due to gravity, then the phrase "not accelerating at all" is, as my two spacecraft example shows, ambiguous.

Edited by Alfred Centauri

Share this post


Link to post
Share on other sites

I think this sounds odd to me, for gravity to not be a force, because I've come across so many places where gravity is still referred to and treated as a force even while the curved spacetime idea of gravity is noted and treated as truth. I didn't realize there was any reason these were incompatible. Hmm . . .

I think the more appropriate general tern is "interaction," thought if the word "force" is used, I really have no problem with that either. In the end, I believe in the general theory that gravity is an interaction involving field quanta, which we can call "gravitons." And that would not make sense at all if gravitational effects were purely a geometric effect and not dynamic at all.

But I think that anyone who knows history pretty much understands that someday, the sooner the better, General Relativity will be improved upon.

Share this post


Link to post
Share on other sites

There is a technical reason why gravity cannot be a force as force is understood in physics. The following is a bit technical but, for what it's worth...

Associated with a force field is a potential. In the case of Newton's theory, the gravitational force is associated with a scalar gravitational potential. In the case of Maxwell's theory of electromagnetism, the electromagnetic force is associated with a 4-vector potential (the scalar electric potential and the vector magnetic potential are components of a 4-vector).

If we wish to model gravity as a force in a Lorentz covariant way, i.e., in a way that is compatible with STR, we find the following:

(1) A gravitational force field from a scalar (spin 0) potential (where the potential couples to the invariant mass-energy) does not bend light.

(2) A gravitational force field from a 4-vector (spin 1) potential (where the potential couples to a 4-current as in EM theory) predicts that waves in the gravitational field carry negative energy and, like the scalar theory, does not bend light.

(3) A gravitational force field from a 4-tensor (spin 2) potential (where the potential couples to the stress-energy tensor) that does bend light and has positive energy gravitational waves doesn't mathematically exist, i.e., the theory is self-inconsistent.

Ultimately, in trying to fix (3), one is led to GTR. Loosely speaking, the difficulty is that a linear theory of gravity as a force field in spacetime doesn't exist because a gravitational field, possessing energy and momentum, must itself gravitate! If you add a term to account for this in (3), you find that you must add another and another and another ad infinitum. When you "sum" this infinite series of corrections, you get the equations of GTR.

A related problem occurs when one tries to quantize a spin 2 field in the same way that the EM (spin 1) field was quantized. Essentially, to renormalize a spin 2 field requires an infinite series of infinite counter terms which means that the theory would require an infinity of parameters!

Edited by Alfred Centauri

Share this post


Link to post
Share on other sites

" One of those possible world lines is special in the following way: the elapsed time between the two events along that world line is larger than any other, i.e., that world line is the geodesic connecting the two events."

"The world line of an object in free fall (free from external force) is a geodesic, i.e., path of largest elapsed time."

Waaaaait a minute. I was expecting this to say "shorter," not "larger." I decided to check and Googled "geodesic." The definition that popped up did say it was the shortest. Did you definitely mean to say larger? If that IS what you meant to say then I am even further perplexed.

If it is shorter, not larger, then I think the condensed version would be that "free fall" is when nothing but gravity is having an influence on an object/objects (supposing gravity does have some effect no matter how far away something is from other stuff, if not, it should instead say "when only gravity or nothing else at all is having an influence . . .") and in such a case (free fall) then the shortest possible path will be taken.

The trouble here is I'm still not clear on how this disqualifies gravity from being a force if the above is correct. Could you perhaps give a definition of what a physicist means exactly when they use the term "force"?

Share this post


Link to post
Share on other sites

On a Riemmanian manifold, a geodesic is the shortest path. However, spacetime is a Lorentzian manifold, i.e., the norm of a 4-vector in spacetime is not positive definite so a Lorentzian manifold is a pseudo-Riemmanian manifold. Don't forget, the "distance" between events in spacetime is a combination of distance through space and "distance" through time. And, the distance through time carries a different sign than distance through space. Because of this sign difference, a (timelike) geodesic is a path of largest elapsed time.

Anyhow, if you had Googled "geodesic general relativity" instead, you might have found this at Wikipedia:

A geodesic between two events could also be described as the curve joining those two events which has the maximum possible length in time — for a timelike curve — or the minimum possible length in space — for a spacelike curve.

Actually, this should not be surprising if you are at all familiar with STR and the so-called "twin paradox". The twin that takes the ride on the spacecraft must reverse direction, i.e., must accelerate, to return to home while the twin that stays at home does not. As a result, the twin that stays at home is older (more time has elapsed) than the twin that returns to Earth.

Edited by Alfred Centauri

Share this post


Link to post
Share on other sites

I am familiar with the twin paradox, but not how this means the shortest/most direct path would take the longest time. Assuming one goes the same speed in both paths, I would expect that taking a longer path would also result in taking more time to travel/that the time gap between the one on earth and the one that was on the ship will get even larger.

I tried looking up a definition for force too, specifying that I'm looking for how it is used in physics, and the basic answer I got looked to be something that interacts with an object to change its speed, direction, size or shape. Since gravity does all these things I'm still unclear on things.

Share this post


Link to post
Share on other sites

Join the conversation

You can post now and register later. If you have an account, sign in now to post with your account.

Guest
Reply to this topic...

×   Pasted as rich text.   Paste as plain text instead

  Only 75 emoji are allowed.

×   Your link has been automatically embedded.   Display as a link instead

×   Your previous content has been restored.   Clear editor

×   You cannot paste images directly. Upload or insert images from URL.

Loading...

  • Recently Browsing   0 members

    No registered users viewing this page.

×
×
  • Create New...