Keep in mind that we don't know what is beyond our "light sphere".
As far as we know, space is being created, and the void isn't even space, so beyond that has little meaning.
You can call areas outside of the observable universe (our bubble) a parallel universe since it would never be reachable, or so we now think (current space-time laws). This is one version of the multiverse. If the universe is infinite then you have these areas that you're never going to reach so thats why in this sense a multiverse.
The speed of light is through space-time so we don't know if there's stuff beyond space-time. But in theoretical physics there is. The brane and the bulk so there's other actual potential physical dimensions. Things that connect blackholes, whats outside of things connecting them. That is often seen as the lowest level of the multiverse and parallel universes.
en.wikipedia.org
We know the universe is expanding primarily through observations of the redshift of galaxies. When astronomers study the light coming from distant galaxies, they observe that the spectral lines in their spectra are shifted towards longer wavelengths, which indicates that the galaxies are moving away from us. This phenomenon, known as cosmological redshift, is consistent with the idea that the universe is expanding, with galaxies moving away from each other as space itself expands. Additionally, other observations, such as the cosmic microwave background radiation and the distribution of galaxies, also support the concept of an expanding universe.
The universe is expanding faster than the speed of light in certain regions. This is due to the expansion of space itself, rather than objects moving through space. According to our current understanding of cosmology, the rate of expansion, known as the Hubble constant, is measured to be about 70 kilometers per second per megaparsec. This means that galaxies that are far enough apart can recede from each other faster than the speed of light. However, it's important to note that this does not violate the theory of relativity, as it is the fabric of space itself that is expanding, rather than objects moving through space at such speeds.
The expansion of the universe is a well-established scientific concept. Beyond our observable universe lies what's often referred to as the "unobservable universe" or "beyond the cosmic horizon," where the light from distant regions hasn't had enough time to reach us yet due to the expansion of space.
We can't directly observe or interact with these regions because the light from objects there hasn't had enough time to reach us due to the ongoing expansion of the universe. Speculating about what might exist beyond the cosmic horizon is a topic of scientific inquiry, but it's currently beyond our empirical knowledge. Some theories suggest that the universe may be much larger than the observable portion we can see, potentially containing more galaxies, stars, and other structures. However it remains speculative.
The consensus for more than 40 years is that inflation happened before the Big Bang. There was this rapid expansion of space-time but the Big Bang is more actually like the dumping of energy into this place. Plank-order seconds after the Big Bang all of this was happening. The Big Bang doesn't have much to do with the expansion of the universe. It has a lot more to do with the dumping pf energy. Mass and energy are fundamentally related and they come from quantum fields. The expansion was already happening and we know the universe is expanding due to dark energy. The Big Bang is just the moment of creation in the sense of the stuff in this place that we know of. Before the Big Bang we know there was only inflation. We can only say from what we currently understand, what happened at the end stages of inflation. Before those final stages of inflation we don't know what happened. Some people think the universe might have started in a singularity. Before those final stages of inflation the universe was very small so people just jump to the logical conclusion of maybe it started in a singularity. Presumably quantum fields also existed before the Big Bang, so we don't know where they came from. It makes sense to say that outside of space-time itself there may not be time because time is part of this thing and its interwoven with space in some weird way. But that would be looking at General Relativity and taking what it says very seriously so it all gets very tricky.
The expansion is primarily driven by dark energy which exerts a repulsive force, causing the universe's expansion to accelerate over time. This acceleration counters the gravitational pull between galaxies and other cosmic structures, leading to the observed phenomenon of galaxies moving away from each other at increasing speeds
Is it expanding infinitely? Why is it expanding? Will it cease to exist one day? How was it even created? The Big Bang?
See above for a few answers
I'll respond to the others…
Is it expanding infinitely? Why is it expanding? Will it cease to exist one day? How was it even created? The Big Bang?
We do not know if the local universe is truly infinite.
I am pretty sure it is expanding (referring to cosmic inflation theory)
I'm less convinced that it underwent superluminal inflation when it was very young (there is a fair amount of evidence that it did, but not conclusive evidence).
The Big Bang is the prevailing cosmological model. There is a lot of evidence to support it.
The Big Bang is an extremely dense state of high energy and its an event on the smallest possible scale at the highest possible energy
The whole idea is as the universe cools you get broken symmetries.
The hypothesis is that the universe originated from quantum fluctuations is a prominent idea in some models of cosmology, particularly in the context of inflationary theory. According to this hypothesis, during the very early moments of the universe, quantum fluctuations in a primordial field (often called the "inflaton field") led to a rapid expansion of space, known as cosmic inflation. These quantum fluctuations served as the seeds for the large-scale structure we observe in the universe today, such as galaxies and galaxy clusters.
The idea is compelling and consistent with certain observations, such as the uniformity and flatness of the universe on large scales, it's important to note that it's still a theoretical framework and subject to ongoing research and refinement. Alternative hypotheses also exist, and the precise mechanism by which the universe originated remains an area of active investigation in cosmology.
The cyclic universe seems very reasonable, but I have no evidence.
I don't know of any good evidence for a perpetual universe, but I still keep my mind open to it.
Heat death matches what we currently know, but so does "the big rip" (if dark energy increases over time). The big crunch is not ruled out, but would take new physics.
However some quantum fluctuation might eventually spark a new reality into existence.
en.wikipedia.org
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