We’ve known that since the 1930s, with the work of Edwin Hubble.
Half Man, Half Wit:
OK, then - what’s your definition of “space”?
Clearly (wdell I say clearly, but you have to have a decent basic grasp of the model) metric expansion such as that occurs in big bang cosmology and the expansion of, for example, a fluid in space in the Newtonian limit can easily be distinguished in a number of different ways.
To cmkeller: where exactly, in relation to space where matter and energy already are, is the space in which they will expand in to?
At times, I too wonder what “space” is. When two photons are approaching one another, out past where the sidewalks end, what medium are they traversing? If they are just two fields interacting with other fields, what are the fields in this nothingness of space where they are about to meet? Chronos, I believe, once said (and I’m paraphrasing badly here) that fields fill up everything and if you can’t measure a field in a region it doesn’t mean it isn’t there - a field of strength zero is still a field. But I can’t imagine nothing. It seems as if there is nothing in a region, then that spot is not there. If it isn’t interacting with anything then it ceases to exist. Can someone help with these concepts?
Where I keep my stuff.
Really, I’m not sure what you’re after. Mathematically, it’s clear-cut, but it’s probably not very useful to talk about pseudo-Riemannian geometry right now. What exactly is the problem you have with my post?
When deep science questions get asked, and the reply is “I can’t explain it without showing you a lot of mathmatical equations you probably couldn’t understand anyway”, it’s rather frustrating.
Carl Sagan, for example, had a talent of trying to relate concepts into a conversational laguage kind of way for the majority of people who don’t have the background in the math.
There are a lot more folks who can do the math compared to the number of folks who can also “translate that into English”.
It is, but that’s not what I meant to say. Rather, I just don’t think it would be very helpful to launch into trying to explain the mathematics or the concepts behind them without trying to find out where the problem lies first.
Perhaps the stuff discussed in this thread might help.
I tried to help in that thread with a balloon inflation example, but while I have a conceptualised idea in my head about the nature of the expanding universe, communicating that idea colloquilly was tough, and it didn’t help j_sum1 much (even assuming my idea/conception was correct in the first place).
And I don’t have the math training to understand the “real” math equations either.
Imagine the skin of the balloon is the Expanding Particle Wavefront of the Big Bang. It is travelling out in all directions, and bringing the field of existence with it.
What is beyond it? Nothing and Nowhere. There are no things there, there is no ‘where’ there, since there is no location outside of the reference of the Universe.
Now if you were to suddenly find yourself outside the field, ie. some unknown place in advance of that particle wave front (presumably attempting to observe it from outside), then you would technically speaking be your own Mini Bang of existence, creating a field of “where” around you and being the ‘thing’ surrounded by ‘no thing’.
Now the interesting thing would be if you were traveling along with that particle wave front, observing in the direction it is travelling.
The only thing I can say to that is “Huh?”.
Half Man Half Wit:
Because there is emptiness within the universe also. So why is that distinct from the emptiness outside the universe?
An empty closet, on Earth, if filled with air molecules. I get that that’s not true emptiness. If you put something in that closet, you are displacing the air molecules that occupied that “emptiness.”
Outer space is, in the main, true emptiness. Out between, say, Earth’s atmosphere (or near-Earth orbit where our man-made satellites are) and the moon, there may be some stray hydrogen or helium atoms, but between those, there is emptiness. When a rocket travels in such an area, it is not (significantly) displacing other matter, it is progressing through the medium which is emptiness.
As our universe expands, as the “surface of the balloon” moves bits of matter and energy further from one another, said matter and energy is logically nothing more than a spaceship travelling through space. There may be nothing out there, but that doesn’t mean that it’s any different from the nothing we already have experience with.
Yes, Hubble showed that the observable universe is expanding. He had no tools whatsoever to say anything about the expansion of space in the landscape’s many false vacua that lie outside observable distances.
Ok, so their is 3 spatial dimensions, in the x, y, and z directions. Being the universe created out of the big bang is finite in size, what would we see at the edges? If we went 13.7 billion light years in the x dimension, what would we encounter if we kept travelling in the same direction? Assume we could somehow get their instantaneously, only so we could avoid the issue of the universe expanding further during the time it would otherwise take to get their. I don’t want to complicate matters too much, but I could ask the same question about the time dimension. What, if anything, existed, say 30 biliion years ago? Isn’t the nothing that existed 30 billion years ago different than the nothing that exists in the vacuum between the galactic superclusters?
(Apologies in advance for my poor grasp of things I’ve read…)
Wasn’t one line of thinking that there is no such thing as ‘nothingness’; that the very ‘vacuum’ of space is actually chock full of energy?
There is a book “Zero - The Biography of a Bad Idea” that goes into this in the later chapters.
But it’s not being “travelled into”, clearly or otherwise. Only in the imperfect analogy of a universe in your mind’s eye is it doing that. You’re trying to imagine something we’re not equipped to imagine, and to describe something we can’t describe in non-mathematical terms.
Honestly, no English-language answer is going to satisfy you, because the only language able to describe it is mathematics. But you can’t just keep throwing in English language approximations and our limited 3-dimensional imagination of what it “might look like” and expect the universe to obey them just because we’re not equipped to imagine them.
At some point, you either have to master the mathematics and read the theories yourself, or trust that scientists have done that for you. But throwing round these words like “nothing”, “expanded into”, and using balloon analogies and so on is just our very poor attempt to translate mathematics into English - and it doesn’t work.
It is frustrating - but it’s not our (mankind’s) fault. We didn’t design it that way, and I’m sure scientists would love it if these things were easily comprehendable and relatable in a non-mathematical way. They do their best to explain it in popular science books and the like, but ultimately the answer is a mathematical one, and we don’t get a choice in that. All we can do is come up with bad analogies, and then people will pick holes in the analogies because they are, when it comes down to it, bad analogies.
There is no emptiness outside the universe, because there is no ‘outside the universe’. For anything (even emptiness) to be there, there’d first have to be some there there, which there isn’t.
And again, the space between galaxies, even though it’s empty, still has certain properties – a metric, certain symmetries, certain laws that hold within it, such as Newton’s, a maximum speed, and if we’re talking about a universe like ours, it’ll also be permeated by quantum fields. None of this is true for ‘nothing’.
I think you’re caught up in a linguistic confusion of the kind my first post in this thread alluded to – you hear ‘there’s nothing outside the universe’, and you immediately wonder what this ‘nothing’ is like, which is only natural, but in effect means you mis-parsed the sentence: usually, if somebody says ‘there is x (which is) y’, it means that ‘there exists a thing called x, of which the property y holds’; so to parse the sentence ‘there is nothing outside the universe’ in this way yields ‘there is a thing called nothing, of which the property ‘being outside the universe’ holds’. But of course, that’s nonsense: there is no ‘thing called nothing’, or if there were, that thing wouldn’t be nothing proper. We’re ill equipped to talk about nothing, just as we’re ill equipped to talk about infinity – they’re just not concepts we have any direct experience of.
This is a bit off topic, but I’m a little ill at ease every time this claim is made. I don’t think it’s really true – after all, every mathematical entity has a definition in terms of language, or if it doesn’t, it has a definition in terms of other mathematical entities, which have a definition in terms of ordinary language, or if it doesn’t, it’s ill-defined; so in every mathematical statement, one could just sub in the necessary definitions, and turn it into a statement of ordinary language, though it would of course be cumbersome to do so, and I don’t think it’d help understanding much. Really, mathematics is just logical reasoning that uses a lot of abbreviations for convenience; I don’t think there’s anything that can in principle only be expressed mathematically (and if there were, I don’t see how anyone ever could get to understand it).
Yes, but the level of complexity is immense and generally can’t be parsed well in English. And each element of a mathematical expression also needs explanation and so on. You end up with a book; and not one that’s easy to parse.
The closest we have is popular science books, which make a fairly good attempt at it.
Otherwise we’d use English, not mathematics.
I’d also like to say that just because something can be useful mathematically, such as the concept of the null set, or zero, does not mean it has any realistic interpretation within physical reality. In other words, calling ‘outside the universe’ some variant of ‘null’ may be meaningful logically or mathematically or definitionally, but it may not have any meaningful relationship to reality. It may be wrong to assume that any absence of stuff is physically allowable, just as, for a long time physicists supposed a true vacuum may exist, only to find that a true vacuum cannot exist due to quantum fluctuations. Physicists like to say “nature abhors a vacuum.” Well, reality may abhor the absence of universe. You may be able to imagine the non-existence of a universe, an ‘outside’ where the universe is not, but, well, it may be turtles all the way down… (and a turtle for every thing you may want to imagine may not exist).
That’s a very good point. Indeed, in order to construct a meaningful physical theory, the mathematical entities it refers to need not exist in any sense (physical, platonic, or whatever else folks may come up with) – I’ve just been reading a bit of Field, who propagates the extreme view of mathematical fictionalism, according to which all of mathematics is merely a useful fiction. In his book Science without Numbers, he manages to carry out a complete axiomatization of Newtonian mechanics without referring to, or postulating the existence of, mathematical entities such as numbers or functions (though I haven’t studied it in detail).