When reading articles about the possibility of different universes, it’s often mentioned that other universes might have different physics than our own. Also, in Stephen Hawking’s miniseries episode on the beginning of the universe, he says that if the physics of our universe hadn’t been exactly what they are, we would not exist, and that these physical laws came about by chance.
Is there any evidence to support the hypothesis that other universes might have different physical laws? Where do they get this idea? And if physical laws come about by random chance, what prevents them from changing? What about the birth of a universe would set these laws in stone? Are we really sure these laws can’t change on us?
It is a hypothesis, not a known fact, both that other “universes” might exist, and that they might have different physics. There is no real evidence (certainly nothing incontrovertible) for either, now, but physicists can have fun working out what the consequences might be if it were so, and maybe, one day, they might even come up with a consequence that is testable.
Incidentally, I am open to being corrected on this, but I have the impression that when they talk about “different physics” they don’t really mean that the actual basic laws might be different, but that certain fundamental physical constants (which, as far as we know now, are arbitrary) might be different. Thus, in any possible universe we should expect f=ma and e=mc[sup]2[/sup] and so forth to be true (assuming they really are true here), but perhaps* c* (speed of light), or h (Planck’s constant), or G (gravitational constant) or any one of a number of others might be different, which could have major effects on how the laws actually play out in practice.
I’m not so sure of this. Why couldn’t e=mc[sup]3[/sup] for example? Or what if the speed of light had nothing to do with energy or mass? Or what if gravity repelled rather than attracted, ultimately filling the expanding universe with a uniformity of particles? I’d say (and I may be wrong about this) that as long as there’s no internal contradiction, any law would be valid.
I’ve seen some web sites that attempt to explain this. (After I finish this post, I’ll try to find one and come back with cite.)
One such site included a diagram showing the inter-relations and interactions of fundamental particles, and another showing how those might be if certain fundamental constants were just slightly different.
The consequence was profound: For example, quarks could not have clumped together to form protons or anything else. Thus, such a universe would consist of fields of free-floating “probability density wave function” or whatever they are at that low level, which would never congeal to form matter.
Nope. In fact every so often there’s scientific speculation that some physical constant is changing over time. There’s also the possibility that we live in a metastable false vacuum, and if something causes a spot of true vacuum to form then it would expand at about the speed of light, our present laws of nature transforming to new ones as it expands and destroys the universe as we know it.
Isn’t there some speculation (or maybe even evidence) that the speed of light has been slowing down lately?
How would we ever detect or measure such a thing, if (as one might imagine), everything else in the universe slows down with it? I think I read about this too somewhere. The evidence comes from studying ancient light coming from billions of light-years away, in which the red shift isn’t quite what it’s “supposed” to be.
I just tried to google that, but the hits I found were mostly popular news reports like ABC or Fox News, and a bunch of “creationist” crap. I assume, without even looking, that the creationist argument goes something like: “See? See? Your false god science can’t get anything right. Therefore creationism is true!”
The fact that “set in stone” means “SET IN STONE” strikes me as suggestive. Got to have the laws be the way they are for stone to exist, and for that term to mean what it does.
Kurt Vonnegut’s novel Slapstick posits a (near) future in which it is discovered that constants such as G being stable for extended time periods is an anomaly. In the story, G changes as often as the weather, and a person who is practically glued to the floor by his own weight one day can be jumping over skyscrapers the next.
I’d like to hear Hawking or other physicists explain the proposition that physical laws came about by chance. I don’t have a dog in this fight; it just seems a fundamentally pertinent question as to the nature of reality. Are physical laws constant, or are they malleable?
Theorists who spend their time chalking up equations on blackboards have only to erase this or that constant and replace it with another to determine that everything would fly apart if the constants weren’t just right, but so what? Is there any problem with the concept that fundamental particles must interact consistently? Why wouldn’t they?
I remember that when other solar systems were first discovered, that they challenged the scientific consensus on how these systems form. You have gas giants orbiting close to stars, which wasn’t supposed to be possible. Could it be that physical laws were different when those solar systems formed, which is why it doesn’t make sense?
I would not say chance had much to do with it. Our current conditions are fairly stable, at least in the near term. Systems which are unstable do not persist: the trend toward greater stability or they become something else. The early picoseconds of our universe’s existence were quite chaotic, then they developed stability, which may have been the result of increasing instability repeatedly transforming systems until ones trending toward stability arose.
In other words, the universe just naturally developed the characteristics it currently has because they are comparatively stable. This may have taken several tries (we might be in bang-cycle 42,386,271,595), or it might be just a normal universal vector of development.
And, of course, to say that different constants would mean we would not exist is questionable. Very possibly something analogous to us, in an unimaginably different form, would exist.
It makes more sense to think that there are some variables in the formation of solar systems that will lead to slightly different results, than to think the laws of physics changed. There are different kinds of galaxies, but no one is suggesting they formed under different sets of physical laws. Different conditions operating within the same physics resulted in differing galaxies, that’s all.
So the theory is that all the constants were established randomly in the early picoseconds?
The question I have is whether there is any proof that there can be variation in physical constants from one universe to the next. This is a hypothesis that cannot be tested, of course, but are there theoretical or mathematical arguments that allow for alternate physics?
I don’t think this question has any bearing on sapient life, by the way. I’m good with the thought that in a vast universe of vast age any random set of physical constants will eventually result in sapience.
Well, there’s no proof, and it seems difficult to me to even envision how one would prove such a thing, but there are definitely mathematical frameworks in which such variation is possible. The most prominent is string theory: you might now that, for consistency, string theory needs for there to be extra dimensions (6 or 7, depending on the version; I’m counting ‘M-theory’ as a version of string theory here), and these extra dimensions, in order to be unobservable, need to be ‘curled up’ or ‘compactified’ to microscopic size in some way.
Now, there’s multiple different ways to perform this compactification; the usual estimate is something like 10[sup]500[/sup]. The precise details of this compactification, however, change the ways the strings wind around and vibrate in these extra dimensions; but this winding and vibrating essentially determines what particles and forces exist.
This multitude of possibilities is sometimes called the ‘string landscape’, and depending on your philosophical preconceptions, it’s either a problem for string theory—since, contrary to prior hopes, it does not uniquely yield ‘our’ laws of physics—or indicates that we live in a multiverse in which all these possibilities are realized, and thus, in which different universes with different physical laws exist; that we find ourselves in this particular universe is then explained using anthropic reasoning.
All of these, by the way, would be universes in which Newton’s laws, the laws of relativity, and quantum mechanics hold, since those are ingredients to string theory. I’m not aware of any proposals in which the basic ingredients of these theories vary; only their content (the precise particles, forces, and coupling constants) is typically assumed to be variable. The question how much variation is actually possible is, of course, a completely open one (Einstein encapsulated it in the question of whether god had a choice in creating the world, his hope clearly being that there is only one way to make a universe, which thus is entirely constrained by necessity; whether or not this hope can be fulfilled still remains to be seen).
We’re pretty sure it has. The last time it happened would correspond to the end of the inflationary era, but it may well have happened one or more times before that.
As for the changing speed of light, it’s not really meaningful to say that c might change. It’s really just a conversion factor between different units, but like all conversion factors, it’s fundamentally equal to 1. When people refer to c changing, what they’re really referring to is the fine structure constant changing: I’d bet a fair amount that it’s not, personally, but it is meaningful to say that it might change. If one insists upon breaking up the fine structure constant into other “fundamental” constants, though, I’d be a lot more comfortable saying that a change in the fine structure constant means a change in the charge of the electron, or in Coulomb’s constant, than in saying that it means a change in c.
