2
$\begingroup$

This question already has an answer here:

I just asked this astronomy question about how far away the light is that would show us the beginning of time, the Big Bang.

Some answers claim that the light I ask about doesn't exist, because "The Big Bang created space and time."

The way I see it, space, true "space" is literally nothing. You can't create nothing. So I would argue that the BB didn't create space, but only filled it.

Can someone please explain why we theorize that space itself was created by the Big Bang?

$\endgroup$

marked as duplicate by Alfred Centauri, Brandon Enright, ACuriousMind, Kyle Kanos, John Rennie Feb 9 '15 at 6:23

This question has been asked before and already has an answer. If those answers do not fully address your question, please ask a new question.

  • 1
    $\begingroup$ How could 'nothing' have a specific number of dimensions? $\endgroup$ – lemon Feb 8 '15 at 20:07
  • $\begingroup$ @lemon easily... $\endgroup$ – CuriousWebDeveloper Feb 8 '15 at 20:08
  • $\begingroup$ possible duplicate of Did spacetime start with the Big bang? $\endgroup$ – Alfred Centauri Feb 8 '15 at 20:09
  • $\begingroup$ Related: Did “big bang” radiate light? $\endgroup$ – Alfred Centauri Feb 8 '15 at 20:12
  • 5
    $\begingroup$ Curious, your response to lemon only shows that you don't understand what "literally nothing" is (not). Moreover, your question is a classic example of dropping context. The Big Bang model is within the framework of General Relativity in which spacetime is a dynamic participant in reality. To claim that space is literally nothing is to reject General Relativity at its root and, thus, the Big Bang model. $\endgroup$ – Alfred Centauri Feb 8 '15 at 20:22
4
$\begingroup$

If you had empty space and then matter expanded from a point in it, then some of the matter would be in the center, seeing everything moving away from it. Some of it would be near the edge and see darkness filling half their world.

We see matter moving away, and it seems unlikely that we just happen to be so close to a center of the universe. So we look for other options that don't require us to be in such a special place. Since we already know that space and time can be curved, when we look for other options, there are lots of really interesting options.

If the universe were 1d you could imagine that at different times, the universe is a circle, later times it is a larger circle. So the radial direction is time, and space goes around in a circle. So what we expand into is ... the future.

If the universe were 2d you could imagine that at different times, the universe is the surface of a sphere, later times it is the surface of a larger sphere. So the radial direction is time, and space goes around in a spherical shell. So what we expand into is ... the future.

Since the universe is 3d we can imagine that at different times, the universe is the surface of a hypersphere, later times it is the surface of a larger hypersphere. So the radial direction is time, and space goes around in a hyperspherical shell. So what we expand into is ... the future.

The advantage of these models is that every point in the universe at a particular time is treated equally. We can then put in specific details about how quickly it expands, the matter and radiation and other fields in it and see what predictions it makes. If it agrees with what we see, we like it but keep checking. If it doesn't agree, then we try to fix it, look for errors, and consider alternatives.

Having the expansion be into the future is nice because that is what happens if you wait. Any part of the universe ends up in future, so maybe the future is just bigger than the present. But if you run that reasoning backwards, the universe used to be smaller in the past. Maybe it contracts towards a point, or maybe something interesting happened when it was small.

It's an area of active research.

$\endgroup$
4
$\begingroup$

"The way I see it, space, true "space" is literally nothing"

Most physicists and I believe many philosophers would disagree. The notion of "Nothing" is impenetrable logically: "nothing" has neither any properties nor relationships with anything else that can be reasoned about. The best you could do would be to assert that "nothing" is somewhat like the empty set: an initial object in a category of things that we want to talk about in physics. Karl Popper, a fashionable icon to cite in modern science, would berate you for including "nothing" in science because, having no properties, one cannot make potentially falsifiable statements about "nothing" .

In stark contrast, "empty space" definitely has properties. General Relativity shows us that empty space is inhomogeneous: the curvature we compute in this piece of empty spacetime here can be decidedly different from that of that piece over there. I'd like to restate Lionel Brits's answer in even more emphatic terms: empty space is not only filled with quantum fields, it is made of quantum fields. We call it "empty" locally when we drive it into its lowest energy state or ground state. We can do this by locking it up in a radiation shielded box and pumping all the molecules out.

If the universe is a so called compact, boundaryless manifold like a higher dimensional analogue of a 2-sphere or the surface of a balloon, then nothing exists aside from the Universe. There is no outside, and the mathematical fields of things like topology and geometry - especially differential geometry - give us the language we need to describe such a thing with no reference to anything outside. One doesn't need to think of these things as embedded in any "outside".


User Chris White makes a comment worth capturing in an answer:

...I feel like pointing out that one doesn't need quantum fields for space to be non-nothingness. Even the anti-absolute-Newtonian-space camp would say space is the set of relations between objects, and those relations are not arbitrary. Even if there were no proper objects in the universe, for there to even be the ability to hypothesize objects with a spatial relation to one another, space must in some sense exist and have properties.

as does user Stan Liou:

I think that you're insufficiently emphatic. Even a simple Euclidean space has nontrivial structure, such as notions of distance and straightness. One of the main points of GTR is the marriage of physical inertial properties and the notion of straigness (generalized to affine geodesics), your point is morally true classically as well. (ETA: heh, ninjas.)

$\endgroup$
  • $\begingroup$ @ChrisWhite I've included your comment. If you want to write your own answer, I'll delete your text from my answer and cite yours. $\endgroup$ – WetSavannaAnimal Feb 9 '15 at 0:15
  • $\begingroup$ @StanLiou See my comment to Chris White, applying equally well to your valid point. $\endgroup$ – WetSavannaAnimal Feb 9 '15 at 0:15
2
$\begingroup$

According to inflation, strictly speaking, space is still being created. I find this idea very interesting. Also, the idea of space as being an empty void to be filled is out of date. Space is full of fields, even when there are no particles present.

$\endgroup$
-1
$\begingroup$

Your question is: why is said that the space is expanding ?
The answer that everyone are aware, by consensus :
We see a reddening of the light received from distant stars and galaxies for the same stellar processes we see in the sun and nearby stars. One way to interpret it, the official way, the only one that your teacher and scientists do know, is: the galaxies are moving away from us in every direction. The space expansion and the BB theory began.


But I've a different description for the same observations, not requiring space expansion:
We measure with atoms and, in all the building of physics, there are not a single word about the 'absolute' size of the atom (I welcome anyone able to provide a link to a paper or textbook that contradicts my sentence):

Below are three images of measuring tapes:
With a larger unit length, a greater atom, we measure less 'space': it is the past.
With a smaller unit length, a smaller atom, we measure more space: it is the present.
Thus, quite naturally, the measure of the space expansion can point to a shrinking atom instead of the space expansion. Obviously this phenomenon can not be measure in the lab, and there is not a simple way to distinguish between the two descriptions.

To those that mention the metric (GR) as a cause I can ask: is it a cause or a description? GR was 'invented' by Einstein well before the space expansion hypotheses and he did not predicted any space expansion.

My description is appealing to your intuition, just 'wording', such that anyone without formal training can interpret correctly what I'm saying.

To those that have the skill and will to read a formal document, can certainly find it.

larger unit length in the past

enter image description here

enter image description here

enter image description here
smaller unit length in the present

$\endgroup$
  • $\begingroup$ There is of course no observational difference between cosmological expansion and everything else shrinking. But it's the everything part that's important: not just atoms, but particle Compton wavelengths, classical electron radius, etc. Everything one could ever use as a ruler should shrink the same, so it's much simpler to say space expands. ... It's no different than, say, time dilation: does time 'really' run slow for moving clocks or is time the same and the moving clocks just wrong? Since every clock, no matter its make, would be affected the same way, time dilation is much simpler. $\endgroup$ – Stan Liou Feb 9 '15 at 5:21
  • $\begingroup$ @Stan. you have so many points that I had to assume that you can read and analyse the 1st doc in my profile. If thinks are so simple why should I bother showing that Mass,Charge,Length,TIME units evolve as the atom, and particles. But the evolution is not linear but exponential and the time unit is not constant. And this is on the antipodes of the usual description. Of course that I understand that it is more rewarding the notion: the space expands without any cause deeply encrusted in our minds (to many a pre-school learning). I offer one explanation for the expansion and you have none. $\endgroup$ – Helder Velez Feb 9 '15 at 13:16
  • $\begingroup$ if you think it's "without any cause", you're mistaken. There's as much cause as in the trajectory of a throwing object making an arc (etc.). What's actually not understood is the origin of the initial conditions, i.e. for what reasons (if any) was it initially thrown as it was. $\endgroup$ – Stan Liou Feb 9 '15 at 22:46
  • $\begingroup$ @StanLiou I googled 'cause of space expansion' and found nothing relevant not even in WP-Metric_expansion_of_space. IMO, your description of 'cause' is a mechanical, ballistic approach, largely condemned by physicists (IMO). $\endgroup$ – Helder Velez Feb 10 '15 at 1:32
  • $\begingroup$ thrown ball is an an analogy, pointing to a common cause: gravity. Of course gravity is not Newtonian, so ballistics can't be taken true, but what they have in common is that they're both solutions to the equations of a theory of gravity: given an initial condition, all else on the large scale follows from gravity. (In the case of cosmic expansion, the FLRW family of GTR solutions.) $\endgroup$ – Stan Liou Feb 10 '15 at 1:41

Not the answer you're looking for? Browse other questions tagged or ask your own question.