Episode 072 - Alternative Explanations in Science, and The Size of The Sun
Date: 05/27/21
Link: https://www.epicureanfriends.com/thread/2004-episode-seventy-two-alternative-explanations-in-science-and-the-size-of-the-sun/
Summary
Section titled “Summary”Don reads Book Five lines 509–613, covering the formation of ether and sky from fine seeds, the motion of the heavenly bodies (with multiple possible causes given), the earth hanging suspended in air by its union with air, and the size of the sun and moon. The panel discusses the three nested entities in Epicurean cosmology — universe (to pan / omnia), cosmos / world (mundus), and the earth itself — along with the etymology of cosmetic and De Rerum Natura.
Extended discussion of Epicurus’s multiple-explanations principle from the Letter to Pythocles: where evidence cannot determine the correct cause, multiple plausible explanations suffice, and the wise philosopher does not pretend to choose. Cassius addresses the charge that this makes Epicurean philosophy anti-scientific, drawing a parallel to Cicero’s criticism of Epicurean political non-engagement, and argues that the Epicurean scientist pursues knowledge because it gives pleasure. Martin notes that light diffraction gives a grain of truth to Lucretius’s claim that the sun and moon appear their actual size.
Transcript
Section titled “Transcript”Cassius:
Welcome to Episode 72 of Lucretius Today. I’m your host Cassius and together with my panelists from the EpicureanFriends.com Forum, we’ll walk you through the six books of Lucretius’ poem and discuss how Epicurean philosophy can apply to you today. We encourage you to study Epicurus for yourself and we suggest the best place to start is the book Epicurus and His Philosophy by Norman DeWitt. For anyone who is not familiar with our podcast, please check back to Episode 1 for a discussion of our goals and our ground rules. If you have any questions about those, please be sure to contact us at EpicureanFriends.com for more information. In this episode 72, we’ll read approximately Latin lines 509 through 613 from Book 5. We’ll talk about the location of the Earth within our world and we’ll discuss Epicurus’ perspectives on science for the sake of science, and the size of the sun and the moon. Now let’s join Don reading today’s text.
Don:
And thus were produced the sea, the air, and the sky, or the ether, spangled with stars. All the finer seeds went to the formation of these fluid bodies, but some were more light than others, and the most light and liquid ether mounted higher and spread over the body of the air, but its liquid parts never mixed with the turbulent blasts of the air below it. The airy region is tormented by violent whirlwinds and disturbed by uncertain storms, while the ether calmly glides and bears along its fires in a fixed course; and that the ether may flow thus gently and in a regular motion, we have an instance in the Euxine Sea, that runs with one certain tide and preserves one constant stream in the current of its waters.
Now let us show from what cause precedes the motion of the stars. And first, if the whole orb of the heavens be moved, then we must allow that the air bounds and encloses the outward surface of the heavens and both the poles. The upper part of this air presses above and drives the skies down to the west, the course in which the stars, the great lights of the world, are to move; and the under part flows below and lifts up this orb from beneath, and makes it rise, as we see the wheels of a mill or buckets are turned about by a running stream. Or perhaps the whole body of the heavens may remain fixed and yet the stars may execute their motions, either because some rapid particles of the sky are shut up and struggling to find a way into the empty space or world about and drag the stars along with them; or some external air rushing in from some other place may turn them about; or they may move severally forward of themselves through the sky where proper nourishment invites them to feed and keep alive their fires. But it is hard to resolve for certain what is the particular cause of these motions in this world of ours.
I rather propose reasons in general for what may be done through the universe, in the multitude of worlds contained in the great all, and formed after various manners; and I offer many causes that may account for the whole, yet one only can be the true one that produced these effects. But to pronounce which it is, no wary philosopher will take upon him to do.
But that the earth should rest in the middle region of the world, it is necessary that its weight should in some degree lessen and be laid aside; and for this end it was fit that another substance should be placed under it, to which from the very beginning it should be united closely by natural and congenial ties, and upon which it should be stayed. This substance being the surrounding air, which is part of the same whole and as it were of a piece with the earth. The earth therefore hangs suspended in the middle and is no weight or pressure to the air at all. And so the limbs are no load to the body of a man, nor is the head a burden to the neck, nor do we perceive the weight of the whole body to press heavy upon the feet. But whatever weight is laid upon us from without, and is no part of us, is a pain to us, though it be ever so small. Of so great concern it is to what every being is severally united.
For the earth was not brought from any other place and entrusted into the strange embrace of a different air, but was formed together with it and became a regular part of the world, as our limbs were produced with the body and are essential parts of it. Besides, the earth when it is shaken of a sudden by a violent thunder makes everything that is upon it tremble, which it could by no means do unless it was closely joined to the airy parts of the world and to the heavens above; for they all stick closely together by common bonds and kindly unite from the beginning. Don’t you observe how the most subtle power of the soul supports the body with all its weight, because it is so strictly connected and so closely joined to it? And what is it that the force of the soul, which actuates the limbs, that raise the body and make it leap nimbly from the ground? Don’t you perceive now what a substance of the most subtle nature is able to do when united with such a heavy body? Such as the air when it is joined to the earth, and as the soul to this body of ours.
But further, the orb of the sun is not much larger nor is its heat much greater than what our senses are a discovery to us. For at whatever distance the fire can send out its rays of light and warm us with its heat, that distance takes away nothing from the bigness of the flame, nor does the fire appear less contracted to the eye. And therefore since the heat of the sun and its diffused light reach our senses and shine upon the earth, you are to conclude that his form and magnitude are no greater nor less than they appear to be.
And the moon, whether she views the world with borrowed light or whether she shoots out her beams from her own body, however it be, she is of no greater size than to our senses she appears; for all objects we look upon at a great distance and through a long tract of air show first irregular and confused before we discover their utmost figure and proportion. And therefore since the moon at once presents to us the certain form and the complete appearance of the whole orb, she shows to us above as great as she really is.
Besides, since all our fires here below, when they are seen at great distance so long as their light is clear and their brightness shines out to us, do seem to change a little and show more or less contracted, we may conclude that the stars we view in the heavens are very little either greater or less than they appear.
Nor are we to wonder how it comes to pass that so small a body as the sun is able to emit so much light, to spread over the seas, the whole earth, and the heavens, and to cherish all things with its kindly heat. For you may imagine that from the sun one large fountain of light breaks out and flows abundantly like a river over the whole world; and that the seeds of fire from all parts of the universe meet in the body of the sun and are there collected as into a spring, from whence the heat of the whole world is diffused abroad. Don’t you observe how widely a small fountain of water spreads its streams over the meadows and overflows the fields? Or perhaps the heat flowing from the small body of the sun may inflame the adjacent air, if the air be properly tempered and disposed to catch the fire from the feeble strokes of heat; and we sometimes see the corn and the stubble to be set all ablaze from one small spark falling upon it. Or it may be the sun shining above with the rosy light has many dark and unseen stores of fire about it, which though distinguished by no outward brightness may yet increase the heat of its rays and make their strokes more inflamed.
Cassius:
Thank you Don for reading that for us today. It looks like we are going to be discussing astronomy again today. This one’s going to be a little bit harder to wrestle with than some of the others because it seems to be kind of specific to some astronomical observations. If we just go back to the very beginning paragraph of what we read for today, it sounds like he thinks that the upper reaches of the atmosphere, which I think he’s calling the ether, is a lot less turbulent than the lower reaches, which I guess is possibly true.
And if I can get on my translation hobby horse just for a second — the fact that the translators usually use the word “world” to actually mean the cosmos, which the way they translate it includes all of the stars and the astronomical phenomena and the sun and the moon and that sort of thing. So I think it’s sometimes hard to get a grip around the fact, because whenever I hear “world” I think of just the earth. But from what I can see, the Greek word cosmos was translated as mundus or mundi in the Latin, and that’s what they’re translating as “world” most often. But then they also have the universe — he talks about “the all” here, so that’s the translation of the Greek word for the universe, to pan, which is translated as omnia in the Latin. But then they also have the earth itself as the earth we walk on, and that’s a separate thing. So we have three separate things that I think are sometimes interchanged: the universe, which is everything; the world or the cosmos or the mundus in Latin, as the system that we live in that has our stars that we can see; and then the actual globe of the earth that we live on ourselves. There’s three separate nested, like Russian dolls, phenomena that we’re living in. And that’s how he can say that the gods live between the worlds, because the world includes the stars that we can see in the sky.
Martin:
Yeah, but except in principle this is correct, but it’s made more complicated in that today’s astronomical take and this classical view don’t really talk about the same thing. Because what we can see includes possibly — we don’t know it for sure — but possibly almost all of the universe, but the ancient Greeks thought these stars are much closer to earth than we think. So that means what we see as a huge portion of the universe, they thought is just a small cosmos, and there’s a lot more around. And that makes it then a bit more complicated.
Cassius:
Exactly. And I was even thinking along those same lines, Martin — that in some respects what scientists today call the visible universe is sort of our cosmos, because we can only see to the microwave background radiation in a sphere, so we’re sort of nested within the visible universe, and there are some who say that eventually the stars are going to go beyond our horizon and that sort of thing. So we have a similar situation, but I don’t in any way want to imply that they had that idea back then. Their view was that there was the earth itself inside of a sphere that had the stars on the outside of it, and that was their cosmos, that was their world system. And just because we can make them sound similar, I don’t want to imply that they are similar between the ancient and the modern interpretations of the universe.
Don, what word are you seeing him use most frequently to discuss everything, or “the all”?
Don:
The Latin uses omnia, the Greek uses to pan — the all. And pan, from pantheistic, that’s where we get that word from Greek. So whenever they talk about everything, it’s either omnia or to pan. And it literally means “the all” or “the everything.” And then within that, you can have a cosmos that is an ordered system. And as a matter of trivia, the cosmos is also where the word cosmetic comes from.
Charles:
Oh, okay. How does cosmetic relate to cosmos?
Don:
Because you put your face in order. You bring order to your face and make it perfect and that sort of thing.
Charles:
That’s interesting. Before you said that, I was about to bring up what might also be a tangent. I always used to think that the title given to the poem was supposed to be an allusion as well to some subset or some collection of everything. When they talk about De Rerum Natura — how do you think, Don, since you’re really into the etymology of the words here, what does De Rerum Natura mean to you?
Don:
My understanding is that it literally means “on the nature of things.” Basically, what he’s going to do, he’s going to talk about everything in the universe in the context of Epicurean physics and lay it out, and here’s how everything came about. That’s my take on the title. It’s just “on the nature of things,” and “things” includes everything that he wants to include. “Things” is, I guess, the key word there — rerum — which a lot of us use every day when we write letters, I guess. That’s the plural of res, if I remember correctly.
And so I’ve always wondered what we were supposed to take from that. And of course, now that I think about it, does he use De Rerum Natura within the poem itself, or is that a name somebody just slapped on it in later time periods? I’m not sure of that either. Sedley includes it somewhere, I would hate to say for sure. But just since you brought it up, I’m quickly looking up in the dictionary here, and you are right — as res is the basic term, and the definitions they give are variously thing, object, stuff, matter, issue, subject, topic, affair, event, story, history, circumstances — all sorts of that. So it’s just he’s basically going to talk about all the stuff. “On the nature of stuff.”
Cassius:
Well, I guess one implication was to ask the question whether he intended to refer to atoms or the elemental particles as the things, or whether he’s talking about the things that we see, or just what he intended us to take from that title.
Don:
I think it’s all of the above, actually, because he literally covers everything from the atoms themselves to human civilization.
Cassius:
All right, well, maybe we should bring it back from that tangent back to where we are, because there are a couple of pretty important issues in today’s text. As we were reading through it, I was trying hard to figure out what we really needed to focus on, and I think one of the things we do need to talk about at some length is the issue of the size of the sun and the moon, which is addressed in the latter part of what we’re dealing with today. But let’s continue to go through systematically — what’s the first of the major issues we should pick out of the early sections?
Don:
I will say one other thing, and I’ll get off the Latin kick, but I thought it was unfortunate that Brown translates one line as “now let us show from what cause precedes the motion of the stars.” And I was looking at some of my other translations, and the word that Lucretius actually uses there is “sing” or “recite.” It seems it would be a lot more poetic if they actually said, you know, I’m going to sing the causes of the motions of the stars. Munro and Bailey both use “sing” here, and that is the literal Latin that Lucretius uses.
Cassius:
You’re right, Munro and Bailey both use “sing” here. And what’s the word again? What’s the Latin word for “sing”?
Don:
Canemus, I believe — “we sing.”
Charles:
No, that’s a very interesting point. Yeah. Because this topic that he’s dealing with is sort of a grand one to be using interesting terminology on.
Cassius:
I did find it interesting the way he talks about the whole orb of the heavens and the air pushing on it. It really does, to me at least, imply that he is talking about a sphere and not a flat earth with a dome over the top of it. Because if the whole sphere is turning, then it sets in the west and rises in the east.
I was going to ask Martin — do you see in this material today additional confirmation that we’re not really talking flat earth, but spherical earth?
Martin:
Yeah. What he writes makes only sense if you really think it through like this. I still remember I’ve seen drawings of a flat earth with a hemisphere on top of it, and that is still conceivable. But I think later on when he talks about the moon and says that the earth is somewhere in the middle, I think this is a bit stronger evidence that he was thinking of the earth as somewhat globular and not flat. But it’s again not really complete. And it’s also blurred by the fact that in this part of astronomy, he got the physics and mathematics completely wrong.
Cassius:
Not to put too fine a point on it — completely wrong is the way to state it, yes.
If we were being thorough here, we would probably try to compare both the Letter to Herodotus and the Letter to Pythocles, because that one really talks about these same subjects in greater detail from Epicurus’ own pen. But I don’t have those in front of me to compare, so we won’t do that today unless anybody remembers particular passages.
Don:
The only one I recall — and I believe it was from the Letter to Pythocles — yes, in the letter to Pythocles he actually says that a cosmos is a circumscribed portion of the universe.
Cassius:
Oh, so he says that explicitly in Pythocles?
Don:
Yes. Cosmos esti perioche ex ouranou — my bad Greek. Well, something to that effect.
Cassius:
Well, that’s a reference we would regularly point to to explain the issue of world versus universe and so forth.
I know that what I pick out in these opening sections is you do see a lot of “ors” here, indicating that he’s recognizing there are several possible explanations for what he’s talking about. And in fact he makes that point specifically — that the wise philosopher is not going to try to determine which one it is. Munro says that “to dictate which of them it is is by no means the duty of the man who advances step by step.”
Don:
And Bailey’s version is: “but to affirm which of them it is, is in no wise the task of one treading forward step by step.”
Cassius:
And that brings me back — I know we’ve talked about it on the forum before — but it brings me back to wondering whether that means that as long as you have multiple plausible explanations for a phenomenon, if that’s enough, or whether you have to continue to investigate and find out the proper one.
I think it’s pretty clear — and many commentators I’ve read seem to make the same point — that it is not necessary for us to take a position that only one of them is true when it’s not possible to do that. When it’s not possible, we should not worry about it. We should simply rest our minds with the fact that there are several explanations that can explain it in a way that doesn’t require it to be caused by the gods. Which, if it did, that would be a source of worry. But as long as we have several that are plausible and make sense, we can stop at that point.
Martin and Charles, is that your understanding of that part of Epicurus?
Martin:
Yeah. It’s not possible to decide which one is the right one, so we cannot find the evidence and we don’t see a path to finding that evidence. This is sort of the right attitude — not to take any of them as definitive, but to move on and be cautious about this. It does mean we should stop, but if we see some new information coming up, we can revisit it. If that is not at hand, then we just don’t go further at that point.
Cassius:
Charles?
Charles:
I agree, and you can see that in the Letter to Pythocles as well.
Cassius:
So I guess my question is then, does the Epicurean go looking for the right answer among the alternatives, or do they just accept it? Are there Epicurean scientists who would go looking for the correct version of whatever theory it is, or do you just accept “yeah, it’s one of these” and go about your day? What are the thoughts on that?
Martin:
Yeah. So a scientist would definitely go for it. The Epicurean scientist would definitely go for finding the truth if he has the methodology and means at hand to figure it out. It’s part of his getting pleasure from what he does. But most Epicureans are not scientists, so for them it doesn’t matter. They don’t have the means to investigate by themselves. And if nothing leads them to it, then they’re just content that there are multiple explanations, each of which on its own is plausible. A non-scientist Epicurean doesn’t have to bother with that.
Charles:
That’s a good distinction — if the Epicurean is a scientist and takes pleasure in research, then he should go ahead and do that.
Cassius:
That’s a good point, Charles. Martin pretty much said what I had in mind. Okay, I have some more to add to that.
This is a very interesting question and I’ve seen it come up in a lot of different contexts, because you will definitely have some people who will argue that these passages mean that the Epicurean is really not even going to be a scientist at all — that the Epicurean basically just needs to know a couple of different alternatives and is going to content himself with that. And you can see people develop that argument and take it to extremes, saying that this just means that Epicurean philosophy is actually a non-scientific or even anti-scientific approach to life, because your search for truth is not as highly motivated as it might be under a different perspective.
Of course I disagree with that perspective. The nub of truth in it is that Epicurus tells everybody that the conclusion of the philosophy is that the greatest good in life — the guide of life — is in fact pleasure. So the greatest good in life is not wisdom for the sake of wisdom. You are not out to discover scientific facts just for the sake of discovering scientific facts. You raise the possibility that inquiry is itself pleasurable, and so that becomes part of pleasure, and that’s a good way to look at it. But from a philosophical position, the goal is pleasure, and the goal is not wisdom.
One more thing I want to say about that — I was reading this morning an article about Cicero and Epicurus, where Cicero was accusing the Epicurean perspective of just being basically destructive of the state, because you must constantly, from Cicero’s point of view, be involved in politics and the sustenance of the state. It’s pretty clear in the texts, even to Cicero, that Epicurus took the position that when an emergency arises and when it is of necessity for you to become involved in politics, it’s definitely proper for you to do it then. But Cicero was taking the position that you can’t wait for an emergency — that it’s the nature of human life that unless you’re constantly involved in political activity to sustain the state, something is definitely going to arise and you’re going to be harmed by it.
I see a direct correlation between that argument and this argument about science, because you could take the position that science is so important that you must constantly be pushing the frontiers of science, and somebody who doesn’t want to constantly push the frontiers of science is thinking short-sightedly because they’re going to be taken down by some new COVID-19 or some disease or a meteor, something they might have been able to prevent if they had pursued science before.
My personal take is that Epicurus would have completely understood that and said that it’s still just a matter of your context. If you’re living in a society that is unstable and has a reasonable possibility of needing you and your expertise, then yes, you’re going to participate in society to protect yourself. And if you’re looking at a scientific issue that has a reasonable possibility of affecting you in the future, then yes, you’re going to pursue it to a conclusion that makes sense. But there is also a practical dividing line in both cases where there’s no right or wrong answer. There’s no god to tell you which of those two things to do. So you must use your own knowledge and your own context to make a decision as to whether it makes sense for you to be involved in politics or to pursue some scientific inquiry further.
Let me shut up.
Don:
As long as you don’t feel passionately about it, Cassius.
Cassius:
I have seen too many of my friends who I talked to about Epicurus say, “Well, my gosh, Epicurean philosophy is just a prescription to be a sloth. You’re just going to sit in your bedroom or your cave and do nothing.” And of course I sometimes get accused of not emphasizing science enough, and I consider that to be an insult, because science and computers and studying nature is clearly one of the smartest things anybody can do. But I have to admit that Epicurus is right: if in the force of all your thinking and concluding about philosophy and the nature of human life, you do need to end up thinking about what is the highest goal — that for which everything else is just a tool — that ultimate goal is not wisdom for its own sake. That’s the whole virtue argument. Virtue is its own reward. Well, wisdom is not its own reward. Wisdom’s reward is pleasure. I’ll stop there again.
Charles:
Well, it sounds like, to sort of briefly go off that then — what you’re saying is that pleasure is subjective. If a person derives pleasure from politics, then they are allowed to pursue that under Epicurean philosophy. If a person derives pleasure from scientific research and pushing the bounds of knowledge, then they are allowed to do that too.
Cassius:
I’d go further than that, Charles. I agree with what you just said, but it’s also clear that we do all sorts of things that we might not find immediately pleasing if that thing is going to bring us greater pleasure or less pain in the future. And so I don’t consider science or inquiry to be a pain, but sometimes it can be — sometimes it’s work. I’m sure Martin can tell us that the pursuit of science is work at times. But whether it’s because you get pleasure out of it or because you’re just an intelligent person who knows that unless you spend some time making sure your government is stable, or understanding whether your car’s brakes are going to fail, or spending time on issues of science and society and politics — unless you do those things, you’re not going to be able to live the full pleasurable life that you otherwise would.
And didn’t Epicurus tell — what’s his name, the geometry student? — didn’t Epicurus tell his own follower to put aside his study of geometry? And that’s even discussed in A Few Days in Athens by Frances Wright. And I don’t think that’s a legitimate criticism. He taught his geometer that the goal of life is pleasure. And so when you have that proper perspective, you can then more readily put things in proper context and give them the attention they’re due at a particular moment.
So I don’t see any contradiction or any reason to be defensive about our position on that.
Martin:
I think there’s no need to comment further, actually. Maybe because you raised it: when I was a young scientist, I found it very frustrating that I could only do these microsteps. And so I found it much more pleasurable to apply scientific knowledge to engineering than to actually push the frontiers of human knowledge as an academic researcher. So I left academia many years ago, driven by pleasure. But of course, if I had not done a PhD in a very applied field and had seen this possibility, I probably would have put a lot more effort into an academic career.
Cassius:
Well, what that brings to my mind is the Platonist and the whole academic approach, both in science and in philosophy — their position that the practical things in life are just by definition lowly and less significant. That life’s really all about contemplation for the sake of contemplation and knowledge for the sake of knowledge, so that academic studies in science are far superior to just practical application.
And my understanding of Aristotle is the exact opposite — that he was very much into amassing as much data as you could on every possible topic and then trying to apply it practically and that sort of thing. So that’s what we have with the pointing up and pointing down in the School of Athens painting. But Frances Wright calls Aristotle pedantic, if I remember correctly, in A Few Days in Athens. You do see certain people who are just so concerned about the trees that they never see the forest, and then you see the forest but never see the trees. You’ve got to avoid both problems.
All right, one thing I did want to mention — literally, as I was reading through this, the whole thing about the sun and the moon being the size that we see them never really made much sense to me and I sort of disregarded it. But reading through the words today, it finally struck me as to what he’s saying. From what I can understand, what he’s saying is that if you see things that are very far away, they’re going to be obstructed by the air, they’re going to be hazy — the whole round tower versus square tower analogy. And the fact that we can actually see the sun being very bright and we can see the features of the moon means it’s not traveling through so much air that it gets distorted. So it’s close enough that its image is not going to be obstructed by a lot of air. And the reason that it’s the size that it is, is because we can see it clearly. Is that the direction he’s coming from, Don?
Don:
Yes, I think that’s exactly the direction he’s coming from. Though I would go further and say that it’s not entirely clear to me what this really means when he says it’s the size that it appears to be, because for example your tower — or anybody, and there have been examples previously in the book — if you see a tower or a castle at a distance, it obviously appears a lot smaller because of the distance. So it’s not clear to me how far away he thought the sun really was, because certainly it’s far enough away that it’s reduced in size to some extent. I would not defend it to the point of saying that you can totally reconcile what he’s saying with what we think about the sun today. But I would say that he’s not saying it’s necessarily the size of a basketball — which I’ve also seen people allege — because a basketball moved very far away gets smaller too, and he knows that. You can’t reach out and touch the sun, so there’s some degree of diminishment based on its distance. It’s just apparently a lot less of a degree than we would know today. And apparently some of the other philosophers knew, by applying geometry to it.
Cassius:
And it’s interesting too that even from an observation standpoint, the moon can look much bigger whenever it’s just rising over the horizon than it does when it’s finally up in the sky. So is it the size it is when it’s on the horizon or when it’s up in the sky? If his real answer was that the size of a thing is what it appears to be, that really doesn’t tell you what the answer is. But I did think it was interesting, at least about the moon, that he acknowledges it could be shedding its own light or it could be reflected from somewhere else — hedging his bets there as well.
Martin:
Yeah, but one more comment on this. I think I recall it from one of the letters, so he gave a more specific reasoning for light sources or fire — that they are somewhat exempt from the rule that applies to ordinary objects like a tower. If a tower is far away, it appears smaller. But he specifically mentioned that even when far away, fire does not look proportionally smaller. And I think this is actually the main reason why he thinks the sun is probably not that small. He’s thinking it’s much bigger than a basketball.
Cassius:
Oh, good point. And what do you think about that argument, Martin? Does light not appear to recede as fast as other things do? He seems to be really specific in that assertion.
Martin:
There’s actually something in astronomy like that. The thing is, when we look at the stars, they have an apparent size, but this apparent size is a combination of the brightness and the diffraction of the light when we observe it through a lens — so our own eyes, or through a telescope. It doesn’t show the stars in the actual size as it would be from projection at the distance if you calculated it. The size we see is much bigger than they actually are if we calculate it through. So under certain conditions, objects can fall outside of the usual proportionality between distance and apparent size. There is a grain of truth in what he’s saying.
Cassius:
I guess what you’re saying is that stars, when we see them in the sky, appear — even though they’re just pinpoints of light — still larger than we might expect them to be. Is that what you’re saying?
Martin:
Exactly. Stars are huge, but they are very far away, and they overcompensate for this. Basically, we would not be able to see a star if it were not for diffraction — what is actually a very tiny point becomes slightly bigger, and the brighter stars really look like they cover more than just one cell of our eye.
Cassius:
That’s really helpful to me, because I’ve never tried to get to the bottom of it. So you’re saying this is not just a totally wrong observation — that things which are generating light appear to be larger to us than you might otherwise expect.
Martin:
Yes. There is some deviation from the proportionality. But the reason why this is particularly clear for light-emitting objects is that anything else which is that far away and is not a strong emitter of light will be invisible to us. So even though by diffraction the same law would apply to non-active light sources, there’s no signal for us to see. That’s also what makes it very difficult to find planets around other stars — we cannot see them directly because the reflected light is normally not enough. But we’ve discovered thousands of them by other means. We can find out properties of them, but we can typically not directly image them the way we can with the moon, because the moon is so close that the reflected light makes it easily visible. The size of the moon as we perceive it is probably given by the ratio of its actual size and distance, without significant distortion by diffraction. The same applies to the sun as well.
Cassius:
That’s all very interesting. I’m getting a little bit concerned about our time. The only other thing I’d want us to address before we’re done with this section is — what did you all think of his argument comparing the wind that upholds the earth with the spirit that upholds the body? The point that our head doesn’t seem so heavy to us, and so forth.
Martin:
He doesn’t know the laws of gravity. This was well beyond Newton. So he just didn’t have the right model for how to handle this, and then of course any explanation he comes up with is based on what they knew at that time. From where we stand, it’s not the right answer. But I think what’s more convincing to me is the sail analogy — you can apply the same model and then use the observation that the wind, just air, if you have a big enough sail, it can move a big ship to considerable speed. With this reasoning he can explain the earth being upheld by air within the means he had. At the end it’s still wrong, but it is an explanation which makes sense within the limited knowledge they had at that time.
Cassius:
Exactly. Yeah, well put. I think what he’s trying to do is equate the fine, subtle particles of the animus that makes us able to move our bodies with the air that upholds the earth — because they both came into existence together. So the air and the earth came into existence together and hold each other up, and the animus and the body came into existence together. And it all goes back to the whole thing: they arose together, and they will eventually be destroyed and go their separate ways. And Martin has just said about the wind and the sails of the ship — that’s a very good one. I don’t think I’ve ever seen that one brought out quite that way.
Comparing the earth hanging in air to the head on the body of a man — that you don’t perceive the weight of it — that’s kind of an interesting twist too. I don’t think it makes a great deal of physics sense, but it probably makes sense to somebody who’s just thinking about it as a common person, because you don’t really worry about your head being heavy most of the time.
Don:
Exactly. You don’t think about your head weighing many pounds. But if you put on a backpack that had the same amount of weight as your head on your back, you would definitely feel it because it was foreign to you — as Lucretius puts it.
Cassius:
Yeah, that’s an interesting argument. And I thought it was interesting the way he tried to bring in the animus or spirit, along with the idea that the air and the earth were created together — I did not see that one coming.
He closes with the discussion of the heat from the sun as well, and the different possibilities that might explain it. Does anything jump out at anybody as worthy of comment on that section?
Martin:
I thought it was quite imaginative.
Don:
Definitely. But he always hedges his bets — it could be this, or it could be that, or it could be that. He doesn’t need to come up with the one reason; here are several that are possibilities.
Cassius:
And I don’t want to go back into all of that once again, but that’s a worrisome argument for some people — that that perspective is questionable. But you can offset that by saying: if you have concluded that you really just don’t have enough information to choose between two or more competing explanations and you go ahead and choose one anyway, well, what the heck does that say about your judgment? That’s an equally or more insulting position to be taking.
And it’s all well and good to say that we’ll become scientists and we will explore further and get more information, but that’s easy to say and not so easy to do sometimes. There are so many things in life that you really are never going to know all the information you’d like, and so you’re going to have to end your discussion of it and either come to a conclusion or set it aside and say there’s no conclusion possible. But you just don’t arbitrarily pick one of the possible examples and say that’s the only one — that does not make any sense.
And speaking of the end of a discussion, that’s right where we are — ready for closing thoughts. Martin, what closing thoughts, if any, do you have for today?
Martin:
I think I’ll just say: sort of. Okay.
Cassius:
All right. And Charles, I’m sorry I’ve kind of talked over you much today and didn’t get as much from you as normally. What are you thinking as we begin to close for the day?
Charles:
I mean, the stuff about having two theories and then choosing one — that was in the Letter to Pythocles. But everything I’ve said has kind of been spoken by Don and Martin already, so I don’t really have any closing thoughts.
Cassius:
Okay. Now, you don’t feel motivated to dispute any of the major points we’ve been discussing today, it sounds like — so that’s good. Okay, well, Don?
Don:
I’m just surprised that we got as much out of this section as we did. I was a little concerned going into it because it was so specific — here’s the reasons for this and here’s the reasons for that, and the moon and the sun are the same size. I was like, I’m not sure how much discussion we’re going to get. But this was a lively discussion, so I’m pleased with our conversation today.
Cassius:
Yeah, it seems like so much of what can seem very dry on the surface can still have a very deep implication. It helps to discuss these things, because there are so many times in the past of my life when I’ve picked up Lucretius and come to a section like this and my eyes would start to glaze over and I’d just put it back down and never make any progress. It helps so much to be able to talk to other people and compare thoughts about things like this. It’s much easier to go through.
Don:
See — there’s the importance of friendship in Epicurean philosophy.
Cassius:
That’s right, exactly right. Somebody may say that it’s a better life to be an Albert Einstein and devote yourself to abstract theoretical science, but those young men sitting on the side of the stream discussing their friendships is really pleasurable and compares very well when you ultimately search out what the purpose of life is. Wisdom for the sake of wisdom doesn’t cut it.
Okay. All right, well let’s close for the day then and we’ll come back in a week and do it again. Thanks once again for a good discussion.
Don:
All right. Have a good day.
Martin:
All right, and see you next week.
Charles:
Bye.