N C More wrote:
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Is the universe real? What is reality? Are we real?
You can drive yourself crazy...or just accept what *is*.
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We are limited to two kinds of experiences: those that originate from sensing of the world outside the mind and those that originate within the mind. The former always represent reality (even if not understood), while the latter can represent both the real and the unreal. The unreal exists only in the mind. A fundamental postulate of science is that objective reality is that which exists independent of any thinking subject
But just because the universe is considered to exist as a physical thing by many people doesn’t make that an *is*. There is ample evidence from that past that many people have thought many ideas to be true that were subsequently proven to be false.
Fram wrote
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Attempt at a definition:
A universe is a group of galaxies whose light can be can be seen by one another, given enough time for the light to reach one another, and the space inbetween the galaxies. (I have to include 'maximal' somewhere, to make certain that you have all the galaxies and not just three or four or so).
Do we have anything that we can observe that fits the description? Yes? That's the universe.
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That definition leaves some unresolved issues. A galaxy cluster is also a group of galaxies whose light can be seen by …etc. The universe and a galaxy cluster cannot share the same definition. Clusters, in turn, group together as superclusters, but we cannot be certain that superclusters are the ultimate building block of the universe. Nor can we be sure that there is such a thing as an ultimate building block of the universe.
Your definition, in terms of ‘light’, omits things that do not emit light and is therefore not sufficiently inclusive. Your use of the word ‘all’ in the term ‘all the galaxies’ shows that you consider the universe to be some kind of collection. Galaxies were known to be separate objects well before Hubble came on the scene. Hubble resolved individual stars of the Andromeda galaxy and verified that galaxies are huge collections of stars. He also verified that Andromeda was not a part of the Local galaxy as some had thought. Notice regarding galaxies that the existence of the container was verified before contents were assigned to it. The same cannot be said for the universe, whose existence has never been directly or indirectly verified.
Fram also wrote:
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That's the universe. Nothing hypothetical, but not a 'thing' but more a group description.
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If the universe is not a thing, then it cannot have physical properties and a history. You are taking the ATM side!
Normandy6644 wrote:
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You're asking questions that Kant answered quite some time ago. For anything within the universe to exist, the universe itself must be taken as a priori, or something taken as true so that everything else can follow. You cannot make any observations or predictions without assuming its truth.
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Kant, of course, was not merely implying that for things to be inside a container there must first be a container
. If Kant were alive today he would change some of his views in light of contemporary neurology. The a priori at the base of all knowledge is the neural system. It is pre-wired to let us recognize many things. The infant is born with not only the neural connections for several reflexes, but with mental templates for hunger, thirst, pain, pleasure, for correlation between the senses and the body location of the sensors, for meaningfulness, and for recognizing and expressing the concept of negation. It seems that even a template for grammar is one of them. It is only with those a priori features that everything else can follow. It is only because of those that observation, prediction, and verification of truth can be made. A universe is not needed to justify the existence of any thing. Rather, it is the universe idea that is now in need of justification, as I have indicated above.
Argos wrote:
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We can infer a likely existence for the universe by directly observing the portion we´re limited to (and it ´s not a small one). This portion has to be contained within a "totum".
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All we can verify by directly observing any sized portion of what’s out there is that certain things exist in that portion. We cannot infer that the universe exists from the fact that we have identified stars to exist, nor from the fact that we have identified galaxies to exist, nor clusters.
As for the claim that the portion is not a small one, the verdict is not in yet. It may be that the observable portion is infinitesimally small compared to what’s out there.
At whatever scale you wish (atoms, stars, galaxies, clusters, superclusters) if there are an infinite number of them, there is no “within”, no containment, no “totum”. Until it is proven that there is not an infinite number of anything, the idea of an infinite number of any cosmic thing is equally likely.