Thursday, 12 April 2018

Lee Smolin's Relationist (Meta)Physics

Lee Smolin is an American theoretical physicist who has contributed to quantum gravity theory. He specifically known for the theory of loop quantum gravity.

Smolin is also a faculty member at the Perimeter Institute for Theoretical Physics, an adjunct professor of physics at the University of Waterloo and a member of the graduate faculty of the philosophy department at the University of Toronto.

In terms of the following piece, Smolin is a very philosophical theoretical physicist and cosmologist who takes philosophical positions on various issues in science. One example of that is his position on the nature of space and time and the things (to use a very broad term) which exist within space and time.

Newton on Space and Time

Smolin expresses what he deems to be Isaac Newton's “hierarchical picture” of space and time when he says that within that picture

atoms with fixed and absolute properties move against a fixed background of absolute space and time”.

Indeed Newton's position (which has been called substantivalism) has it that space and time are themselves things (for want of a better word). That is, space and time are things which exist independently of all the other things "within" them.

Smolin concludes by saying that this Newtonian picture is “quite dead”.

Smolin is what philosophers would call an anti-essentialist. That is, Smolin doesn't believe that there are “intrinsic properties”. Instead, as he puts it, “all properties are about relations between things”.

Thus, in the quote above, Smolin used the words “absolute properties”, by which he meant:

absolute entities” = entities with "intrinsic properties"

Thus if entities have intrinsic properties, then those properties will neither change over time nor will they be changed by other entities or conditions. (Unless the entity concerned simply stops existing as the entity that it is.) According to Smolin, it's this ostensibly unchanging nature of intrinsic properties which makes them “absolute”.

Such much for absolute entities. What about Newtonian space and relations?

It's not immediately clear why Newton's position on space would automatically exclude a “relationist” take on things/atoms. After all, “atoms with fixed properties” may still partake in relations even if space is fixed and also if the atoms within space have absolute properties. Why can't we have absolute properties and things which partake in relations?

Smolin's alternative picture to this is a “relational” or “dynamical”. It's a case of spacetime itself - and all properties/things/atoms within it - being relational or dynamical. In other words, in Smolin's universe, literally nothing is absolute or intrinsic.

Leibniz on Space and Time

Smolin then cites Gottfried Leibniz as a relationist. Or, at the very least, he sees Leibniz as being a relationist when it comes to space and time. So, unlike Newton, Leibniz

wanted to understand [space and time] as arising only as aspects of the relations among things”.

Smolin sums up the two opposing positions when he says that “this fight” is

between those who want the world to be made out of absolute entities and those who want it to be made out of relations”.

Smolin adds that this opposition is a “key theme in the story of the development of modern physics”.

In terms of Leibniz again, Leibniz's position (as expressed by Smolin) is that space and time don't exist – at least not as independent phenomena. Space and time essentially arise as ways of making sense (as it were) of the (as Smolin puts it) “relations among things”. In other words, space and time are the means by which we plot the relations among - or between - things. That basically means that if there were no things, then there would be no space and time either. That is, space and time aren't (to use Smolin's word again) “absolute”: they're a consequence of things and their interrelationships.

Nonetheless, if space and time don't exist, then what are these things moving about in? It can be supposed, of course, that both space and time come into being as soon as there are things which have relations with one another. But how does that work? Even if space and time do spring into existence as soon as things spring into existence, then it's still the case that things move about in space and exist through time.

So here are two alternative conclusions:

i) Space and time depend on things and their relations.
ii) Things and their relations depend on space and time.

The obvious way out of this opposition is simply to say that there's no hierarchy involved here: spacetime and things depend on each other. That is, space and time aren't more important (or fundamental) than things; and things aren't more important (or fundamental) than space and time.

What's called “relational theory”, however, is indeed eliminativist about space. This theory has it that if there were no things, then there would be no space either. Relational theory is eliminativist about time too in that if there were no events (in space), then there would be no time.

Smolin's sums up his non-Newtonian (or Leibnizean) position when he states (in his Three Roads to Quantum Gravity) that it's

absurd in general relativity to speak of a universe in which nothing happens”.

Relationism or Relation[al]ism?

Smolin explicitly states his relationist (or Leibnizean) position in the following:

There is no meaning to space that is independent of the relationships among real things of the world. ...Space is nothing apart from the things that exist. ...If we take out all the words we are not left with an empty sentence, we are left with nothing.”

However, there may be a problem here with the use (above) of the word “relationist”. That's because there are in fact two different words which are often used within this metaphysical context: “relationism” and “relation[al]ism”. Prima facie, they denote two (slightly?) different positions. However, on analysis, the distinctions between them appear to break down – at least in certain respects.

On my own reading, Lee Smolin seems to go one step beyond what's called “relationism” and delves into the domain of “relation[al]ism”. What I mean by that it can be said that relationism simply emphasises the relations between things: it doesn't deny that things exist. With relationalism (with an added “al”), on the other hand, “things exist and function only as relational entities”. That is, if there were no relations, then there would be no things. Relationism, on the other hand, simply notes the importance of relations between things; it doesn't claim that things - in and of themselves – don't exist.

Nonetheless, even if these definitions are incorrect (or if I've misnamed Smolin's own position), it's still the case that there's a difference between what can be called the eliminativist and the non-eliminativist position on things.

Thus relationalism is like ontic structural realism (which will be discussed later) in that the latter eliminates things from its metaphysical picture (“every thing must go”). Relationism, on the other hand, simply places relations in an important position in the metaphysics of things.

Having said all that, it's hard not to see the importance of relations even if one accepts the existence of things as independent entities. (Of course the metaphysical notion of independence would also need to be cashed out.) On the other hand, it's also hard to accept (prima facie) the elimination of things from the metaphysical picture. 

Moreover, one can also see the vital importance of relations when it comes to physics. On the other hand, one can't really see how things could be entirely eliminated from physics either. (This may also ultimately depend on how the word 'thing' is defined.)

Yet in (“analytic”/pure) metaphysics one can indeed conceive of (or imagine) a metaphysical picture in which things don't exist. One could also imagine a picture in which things don't have any relations (at least no causal relations) to other things or indeed to anything. These scenarios could constitute the metaphysical natures of particular possible worlds. Though, since Smolin is dealing with the actual universe, it's hard to make sense of such metaphysical eliminativism when it comes to physics itself.

Nonetheless, relation[al]ism can also be read as not actually being eliminativist at all. After all, this metaphysical position may simply have it that things (or entities) aren't what's called “self-standing”. To put that another way: what makes things the things that they are may be their relations to other... things. Or we can even say that particulars (things) are essentially relational. Alternatively, we can say that all a thing's properties are relational. That is, it has no “intrinsic properties”.

Thus, in a weak (or even strong) sense, if all things only have relational properties (and such properties literally make all these things the things that they are), then there is a sense in which things are indeed eliminated from the metaphysical picture. To put that simply: if a thing's relations (or relational properties) were eliminated, then it would no longer be that thing. Indeed it would no longer exist.

Relations and Structure

Despite all the above, it's still hard to make sense of the idea (to use Smolin's words) that “the world is [only?] made of relations”. What does that mean?

This question also relates to the metaphysical position known as scientific structuralism (i.e., in the philosophy of science). Here too relations and structures are deemed to be fundamental. Yet two similar questions can also be asked here:

i) How can there be structures without things?

ii) How can there be structures without space and time?

Relations and structures may well be of utmost importance in both metaphysics and physics. Nonetheless, surely there are no relations and structures without things (or even substances).

So, again, how can the world be “made out of relations” alone? The same goes for Smolin's other claim that “all properties are about relations between things”.

And what does Smolin mean by the words “all about”? We can easily accept that relations between things are important. But so too are things and their properties. So how is it that properties “are [only] about” the relations between things? In other words, is this part of an identity statement? Namely:

properties” = relations between things

There are indeed properties which are relational. However, it can be argued that not all properties are relational. Indeed isn't it the case that in order for some properties to be relational, other properties need to be non-relational?

As for the elimination of things. Take this simple sentence: “x is bigger than y.”

In order for x to be bigger than y, both x and y need to exist as things (or at least as something). It's true that the property (or universal) IS BIGGER THAN may be seen to have an abstract non-spatiotemporal nature. However, the original statements was “x is bigger than y”, not simply “is bigger than”. That is, we're not simply talking about the abstract property (or universal) IS BIGGER THAN.

Despite that, there may indeed be certain relations (or relational properties) which don't involve concrete things. (There are relations between numbers, for example.) However, if we return to Smolin, it's not the case that he's talking about relations between abstract entities even if the relations themselves can be deemed to be abstract.

Ontic Structural Realism

Smolin elaborates on his relationist universe firstly by saying that if

the only meaningful things in this theory are relationships between real things”


it doesn't make sense to talk about space being made up of different parts, or time being made up of distinct moments, unless the points and the moments can be distinguished by what's happening there”.

Here Smolin's position is fairly close to another structuralist position in the philosophy of science. Namely, the contemporary philosophical metaphysical position (as usually applied to physics) of ontic structural realism. In the ontic structural realism picture, “it doesn't make sense to talk about” things with their own determinate (or intrinsic) properties when these things “can only be distinguished” in terms of their structures and relations to other things (within spacetime). In simple terms, the “things” of ontic structural realism can only be distinguished in terms of their mathematical structures and relations. There literally isn't anything else.

In terms of Smolin's own picture, spacetime itself can only be distinguished in terms of (in Smolin's own words) “what's happening there”. That is, what's happening at specific spacetime points. And what's happening at specific spacetime points is invariably a matter of dynamical non-intrinsic properties and their mutual relations.

So just as spacetime works as a means to plot dynamic properties and things together, so ontic structural realism has it that things are mere placeholders used to plot relations and structures together.

Loop Quantum Gravity

Lee Smolin updates his relationism by tying it to the scientific theory of “loop quantum gravity”. Smolin also ties loop quantum gravity theory itself to relativity and quantum theory. Or as Smolin himself puts it:

I believe that the main lesson of relativity and quantum theory is that the world is nothing but an evolving network of relationships.”

Thus Smolin explicitly ties Einstein's general theory of relativity to his own relationist position. Smolin believes (as stated in his The Trouble With Physics) that in the general theory of relativity

[t]he geometry of space and time changes and evolves, as does everything else in nature”.

What's more, “[w]e no longer have fields moving in a fixed-background geometry”. Instead,

[w]e have a bunch of fields interacting with one another, all dynamical, all influencing one another, one of which is the geometry of spacetime”.

Smolin christens this a “background-independent theory”. He defines this position as one in which

[n]either space nor time has any existence outside the system of evolving relationships that comprises the universe”.

Indeed this soup of interrelating fields not only creates spacetime, it also creates the particles and all the other entities/conditions which exist at a specific point in time and place in space.

As just stated, Smolin makes his metaphysical relationism more concrete by tying it the physicists' notion of a “field”. More specifically, he ties it to the theory of “electric fields”. According to Smolin, “physicists using general relativity” can't

speak of a point, except by naming some features of the field lines that will uniquely distinguish that point”.

Moreover, this “network of relationships evolve[s] with time” and is “constantly changing”.

Specifically in terms of “loops”.

The loops of loop quantum gravity theory describes the nature (or structure) of space. That is, loops are extremely small (the size of a Planck length) and they make up the “fabric” of space. Loops are also called “spin networks” (which provides a “spin foam”). Thus both matter and space (in the loop quantum gravity picture) are deemed to be “atomic” (this word is used very loosely in this context).

Another way of describing this is to say that in loop quantum gravity space and time are quantized. That is, space and time are made up of the aforementioned “atoms”. Or, more technically, space and time are seen to be “granular and discrete” in the same way that the quantities (e.g., photons, etc.) of electromagnetism (or energy) are seen to be discrete in quantum theory. This means that space, time and energy can be quantized precisely because they're discrete (or atomic).

Smolin himself says that

what's wonderful about the loop picture is that it's entirely a picture in terms of relations”.

It is these loops which are relational and dynamic. And, by inference, loops make up our relational and dynamic spacetime.

In more detail, in this picture it's the case that there's

no preexisting geometry for space, no fixed reference points; everything is dynamic and relational”.

What's more, Smolin claims that

[t]his is the way Einstein taught us we have to understand the geometry of space and time – as something relational and dynamic, not fixed or given a priori”.

So whereas Newton believed that space and time are fixed; Smolin rejects that position by claiming that there's “no preexisting geometry for space” (or “no fixed reference points”). That means that we have a spacetime with a geometry that's “relational and dynamic”.

However, it's almost certainly the case that Einstein would never have expressed his own position in Smolin's own way. Nonetheless, Smolin's words may well still be an accurate (or faithful) reworking of Einstein's essential position on spacetime geometry.

Loop Quantum Gravity vs. String Theory

Smolin specifically counterposes loop quantum gravity with string theory. As Smolin puts it:

In string theory one studies strings moving in a fixed classical spacetime. ...what we call a background-dependent approach. ...One of the fundamental discoveries of Einstein is that there is no fixed background. The very geometry of space and time is a dynamical system that evolves in time.”

Indeed Smolin (along with such people as Carlo Rovelli, John Baez and Abhay Ashtekar) have rejected string theory precisely because he deems it to have retained the (Newtonian) notion of “absolute space”. Loop quantum gravity, on the other hand, upholds “backgroundlessness”.

So here again Smolin allies himself with Einstein and connects his own “background independent” theory to his metaphysical relationism.

Let's sum up Smolin's overall relationist position.

Smolin isn't only talking about things and their relations: he also sees the geometry of space and time as being relational. Indeed one can says that the geometry of spacetime is relational/dynamical precisely because things and their relations are also relational/dynamical.


No comments:

Post a Comment