Science, Physics, & Philosophy

[Jonathan Wienke]

New thread to continue the rabbit trail started in the HCB cropping thread on its own.

Yes, photons can be counted and measured, and I would consider them to be observable, even though the mechanism(s) by which the magnetic and electrostatic forces that form them propagate through space are unknown.

Similarly, gravitational force (and the related warping of spacetime) can be measured, even though the mechanism by which gravitational force propagates through space is unknown.

If "gravitons" exist, they are currently unobservable, but that doesn't mean gravity (the force accelerating massive particles toward each other and the associated warping of spacetime) is "unobservable" any more than photons are, even though we don't know what particle(s) (if any) carry electrostatic and magnetic forces through space. If something can be measured, it's not an "unobservable". You can't measure something you can't observe.

Re dark matter and energy, its existence is currently unproven--all attempts to detect its existence directly have failed so far. As a theoretical construct, it resolves some discrepancies between various models of the universe and observations, but it's also possible that some other factor or factors are responsible for the discrepancies between the models and the observations.

The discrepancy between theory (excluding dark matter/energy) and observation is observable and can be measured, but the cause of the discrepancy has not been definitively established. Dark matter/energy may be the most plausible explanation for the discrepancy so far, but it's still possible that new discoveries about the nature of gravity, light, or spacetime could account for the discrepancy between theory and observation without requiring the existence of dark matter or energy.

[Telecaster]

Well, photons are themselves force carriers. Bosons. They propagate electromagnetism. You can also think of them as point-like excitations in an electromagnetic field rather than as discrete objects.

Dark matter. Stuff that doesn't interact with electromagnetism and thus can't be seen. Yes, it's strictly theoretical at this point…a means of explaining various observed gravitational anomalies such as the orbital speeds of stars near the outer edges of galaxies (given their speeds the stars should be flung out of their galaxies, but their orbital trajectories show otherwise) and the magnifying properties of gravitational lenses (too high or just too unusual to be accounted for by the observed mass of the lenses). There are various proposed modifications to general relativity that attempt to account for these anomalies without invoking a new thing like dark matter, but they all have unresolved issues too.

Dark energy is even more mysterious. Observations indicate the observable universe is expanding, and accelerating in its expansion. How to account for the acceleration? "Dark energy" is just a placeholder term for something we don't (yet) understand. Is it the cosmological constant in Einstein's general relativity equations? (He initially set this constant's value to zero, assuming a static universe, but allowed it to float after data gathered by Hubble & others pointed to an expanding universe.) That is, is dark energy a property of the universe? Or is it a thing or force in the universe? Dunno.

Lotsa juicy stuff for physicists to chew on!

[Edit: corrected spelling error (propagate).]

-Dave-

[Ray]

Yes, photons can be counted and measured, and I would consider them to be observable, even though the mechanism(s) by which the magnetic and electrostatic forces that form them propagate through space are unknown.

Similarly, gravitational force (and the related warping of spacetime) can be measured, even though the mechanism by which gravitational force propagates through space is unknown.

But is it really similar? That is the philosophical point. Is there not a distinction to be made between forces which can be reduced to individual particles and/or waves and reproduced and created at will through human technology, and blocked at will through the creation of shields.... and something which is a pure force we call gravity, as invisible as Dark Matter or Dark Energy, and completely uncontrollable in the sense that we can't block it or generate it at will? There's no such thing as an anti-gravity shelter.

If "gravitons" exist, they are currently unobservable, but that doesn't mean gravity (the force accelerating massive particles toward each other and the associated warping of spacetime) is "unobservable" any more than photons are, even though we don't know what particle(s) (if any) carry electrostatic and magnetic forces through space. If something can be measured, it's not an "unobservable". You can't measure something you can't observe.

By the same logic, Dark Matter is observable because we can measure the effects of it, using our giant telescopes and other devices to calculate the behaviour of distant galaxies and the rate of expansion of the universe. What happens if in 30 years, or 50 years or 100 years time we still haven't been able to 'observe' any particle or wave which fits the role of a graviton or dark matter? What I'm positing is that just maybe the force of gravity, as opposed to its effects, is a type of illusion, as string theorist Professor Eric Verlinde claims.

[Jonathan Wienke]

By the same logic, Dark Matter is observable because we can measure the effects of it, using our giant telescopes and other devices to calculate the behaviour of distant galaxies and the rate of expansion of the universe. What happens if in 30 years, or 50 years or 100 years time we still haven't been able to 'observe' any particle or wave which fits the role of a graviton or dark matter? What I'm positing is that just maybe the force of gravity, as opposed to its effects, is a type of illusion, as string theorist Professor Eric Verlinde claims.

No. We don't know if dark matter even exists, or whether some refinement to our understanding of spacetime or gravity or something else will alter the equations used to describe them such that they balance out without the requiring the placeholder term we currently call "dark matter". All we know currently is that there is a discrepancy between the math and the observations. It's possible that dark matter is a real thing, but it's also possible that it's a mathematical artifact that will disappear if we discover a new equation for gravity that goes an additional step beyond Einstein's update to Newton's original equation.

Ongoing experiments with quantum gravity (gravitational interactions at the atomic/subatomic level) indicate that some refinement to gravitational theory is probably in order, but exactly what that refinement may be is still unclear.

Interesting times for physicists, indeed.

[Ray]

So would you agree, Jonathan, if we eventually discover that dark matter, dark energy, and gravitons really do exist, and we are able to quantify and study the characteristics of their fundamental particles/waves, or whatever, then we can logically declare that such forces are observable?

Furthermore, if such particle/waves, whatever, are never discovered and we end up modifying our theories of gravity in a perhaps a radical way, would you agree that in retrospect it would be true to say we were deluded in thinking that we had 'observed' the forces of gravity, and that we had in reality only observed their effects and concocted only plausible theories of explanation, such as the possible existence of an unobservable graviton? 

[amolitor]

If the point of the thread is to see how much philosophy one can do with vague and colloquial definitions of 'observable' and 'unobservable' I am going to speculate that the answer is 'not much'.

[Jonathan Wienke]

So would you agree, Jonathan, if we eventually discover that dark matter, dark energy, and gravitons really do exist, and we are able to quantify and study the characteristics of their fundamental particles/waves, or whatever, then we can logically declare that such forces are observable?

If some means is discovered to prove the existence of gravitons, dark matter, or whatever, and measure their properties, then yes. But we're not there yet. At this point it's possible dark energy/matter is an accounting error.

Furthermore, if such particle/waves, whatever, are never discovered and we end up modifying our theories of gravity in a perhaps a radical way, would you agree that in retrospect it would be true to say we were deluded in thinking that we had 'observed' the forces of gravity, and that we had in reality only observed their effects and concocted only plausible theories of explanation, such as the possible existence of an unobservable graviton?[/quote]

No, because the force is the effect. We can measure the force we call gravity, therefore it is observable. There are aspects of gravity that are currently unobservable; we do not know exactly what causes the force, or exactly how it propagates. Perhaps gravitons exist, perhaps they don't. One possible test might be to see if gravitational force is quantized--limited to discrete energy levels. If so, that would support the argument for some kind of gravitational particle. If not, that might indicate gravity is a raw force that doesn't have a particle.

[LKaven]

Jonathan, I might recommend reading Richard Boyd's "How To Be A Moral Realist", which introduces Scientific Realism in contemporary philosophy of science.  [As Boyd says, "I might have equally called it "How To Be A Scientific Realist".]  It's a serious piece, and it's withstood a lot of examination in the years since it was written without being taken down.  In particular, it gives a context over time for some of the terms that appear in this discussion, and will help you decide where you want to put your stake in the ground.

[mezzoduomo]

If the point of the thread is to see how much philosophy one can do with vague and colloquial definitions of 'observable' and 'unobservable' I am going to speculate that the answer is 'not much'.

The point of this thread?  "Mine is bigger than yours."

[LKaven]

The point of this thread?  "Mine is bigger than yours."

Unless people read the primary literature on the subject, there isn't much point in speculating, no matter how smart one is or thinks one is.

[Isaac]

CliffsNotes ?

Richard Boyd, "How to be a Moral Realist"

Richard Boyd, "How to be a Moral Realist"

…

[LKaven]

Better to read the original in my opinion.

[Telecaster]

The issue with gravity isn't whether or not it's real but whether or not it's fundamental. The solidity of my right hand is real…I can grasp things with it, cause things to move & stop things from moving with it, etc. Yet at atomic scales that same hand is mostly the space between nucleii & electrons and between individual atoms. Its solidity is emergent, not fundamental. Maybe gravity is kinda like that. Maybe not. Attempts at a quantum theory of gravity naturally start with the assumption that there are quanta of gravity: gravitons. Whether or not we ever find such quanta has no bearing on their existence or non-existence. The parameters of reality aren't bound by our ignorance.  

I agree that a discussion such as this can't & won't go very far without a solid grounding in the basics.

-Dave-

[Isaac]

Better to read the original in my opinion.

I daresay not that many LuLa readers have a copy of "Essays on Moral Realism" at hand, and the pages missing from Google Books preview "How to be a Moral Realist" might be a problem.

[LKaven]

I daresay not that many LuLa readers have a copy of "Essays on Moral Realism" at hand, and the pages missing from Google Books preview "How to be a Moral Realist" might be a problem.

Did you not link to the full text PDF in your second link? 

[LKaven]

If you've found a full text PDF somewhere on those pages, then please provide the URL to the pdf.

Oh sorry!  It looks like the PDF that was up earlier is not up any longer.  I saw it just recently.  Do you have a place where you could put it up if I send you a copy?  PM me with your email if you'd like, and I'll send it.

[LKaven]

I could send a copy to a few people who PM me with their email address. 

[Ray]

But we're not there yet. At this point it's possible dark energy/matter is an accounting error.

Wow! That would certainly be some accounting error. 

We thought we had identified and labelled all the various types of matter and energy in the universe, then realised through the application of our accepted theories of gravity, to new observations made possible through the improved technology of telescopes, that what we can see or discern, or detect  in any way, is only 5% of the stuff out there. 95% of it is totally invisible and undetectable. More than a slight error, wouldn't you say.   

[Jonathan Wienke]

Wow! That would certainly be some accounting error.

Yes. But it wouldn't be the first time theoretical predictions have been off by orders of magnitude.

[Ray]

Yes. But it wouldn't be the first time theoretical predictions have been off by orders of magnitude.

Now you know why I'm sceptical about the claims of anthropogenic climate change.