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The best-fit model to observational data is a spatially flat, and consequently, spatially infinite, universe. It is spatially infinite today and it was always spatially infinite in the past.
The “initial singularity” is not part of the universe. It is a moment, a point in time that does not exist; only subsequent points in time do. There are points in time arbitrarily close to the singularity. The closer a point in time is to the singularity, the denser and hotter the universe is. But still infinite.
Yes, things that are very far apart today would have been very close in the early universe. But that does not mean that they originate from a single point. Only that they were very close. And no matter how great a distance you name, no matter how early in the history of the universe you go, you will always find things that are farther apart than that distance.
Things would be different if we lived in a positive curvature, spatially closed universe. Such a universe would have a finite volume, and earlier in its history, it would have had a smaller volume. Extremely close to the singularity, its volume would have been extremely small. But even in this case, the singularity itself is not part of the universe. Anyhow, this is hypothetical; there are no indications that we live in a spatially closed universe, and there are plenty of indications that we don’t.
observed or detected but can be inferred from gravitational effects.Answer
- scientists don’t know why.
- A day on Venus is longer than a year on Venus, meaning that Venus rotates on its axis much more slowly than it orbits the sun.
- There are more stars in the universe than there are grains of sand on all the beaches on Earth.
- The largest known structure in the universe is a cluster of galaxies called the Hercules-Corona Borealis Great Wall, which is 10 billion light-years away and over 10 billion light-years long.
- The universe is estimated to be around 13.8 billion years old, but due to the effects of time dilation, it’s possible that some regions of the universe may be older or younger than others.
- If you were to fall into a black hole, the process of spag hettification would cause you to be stretched out into a long, thin strand of matter.
- The universe is mostly made up of dark matter and dark energy, which cannot be directly
- There are more atoms in a single grain of sand than there are grains of sand on Earth.
- It’s possible that there are parallel universes or multiple dimensions of reality that we cannot directly observe or interact with, according to theories such as string theory and the many-worlds interpretation of quantum mechanics.
- We don’t know about what, if anything, was before the Big Bang. Of course, this doesn’t stop people from speculating and sounding like they know.
There is good evidence for the Big Bang as it is left lying around in the universe and what that stuff is doing. We can be confident that the universe was once extremely compressed and extremely energetic and that after the Big Bang, the universe developed in a way that is consistent with known physics. This shouldn’t be a surprise because “known physics” is modelled on the observed universe.
- The problem is that when you try to work back to back in time to the instant of the Big Bang, the physics gets confusing. When physicists find they are in this kind of muddle, the usual strategy is to gather data and then find equations and models that match the data. Unfortunately, all the data available comes from this universe and in the time after the Big Bang. We’re stuck! It’s like trying to build a car using a cake recipe or something. If we had just one reliable observation from before the Big Bang (if there was anything) or from another universe (if there are any), that would be incredibly illuminating and provide enormous guidance to physics, but there appears to be nothing available, and there is probably no hope of ever getting any of the data we really require.
in this situation, physicists have to make stuff up. They don’t make up random stories (like the universe was vomited up by a giant tortoise, or something) but try to form models that are consistent with what they think are deeper underlying principles of physics. Unfortunately, no one actually knows what these deep underlying physics principles are either. We have to make a guess about that too.
- The universe from nothing is one such idea. Or more correctly, one “group” of ideas: most of these speculations come in multiple versions and may overlap with other speculative models. The general idea is there is a background vacuum realm that is even more empty than empty. It doesn’t even have special dimensions and maybe not even time. This is basically impossible to visualize; you just have to kind of believe it or not. What this proto-space does have—or is assumed to have—is quantum fluctuations, a little like the quantum fluctuations in the “empty” space in our universe that can produce random particles. Here-and-there, every now-and-then—whatever that means in realm with no space and maybe no time—a tiny little bit of real space is created by quantum fluctuations. If this bit of space is too small, it might just disappear, but if it has a critical size, it grows in a kind of wild runaway process into a universe, aka a Big Bang. The energy of the Big Bang is provided by the gravitational potential energy of the new space itself (I believe).
- Is there any evidence for this? Nothing, or almost nothing. There is just one key bit of evidence: our universe has not been around forever; it or at least the current form of it, did start somehow, about 14 billion years ago.
This is just one model out of many. It has a bit of inner logic, but it has no real evidence and isn’t even fully worked out. No one has seen the proto-vacuum; it is highly speculative. We just know that the universe exists and we guess there is some kind of cause, even if it is just a random fluctuation. Hopefully, someday someone will come up with a model that fits all known observations and is internally self-consistent, plus is simple enough and doesn’t have too many arbitrary elements, but we aren’t there yet. We have a bunch of partially worked-through speculations and physicists chatting about them in their
But ‘nothing’ is a subtle and complex idea, and the naïve (new, inexperienced) views of it that you or I may have are also naïve in the sense of over-simplistic, or just plain wrong. But we can still say quite a bit about nothing, and in particular that some people think might have been the start of things. And to look at that, let’s
T. Toth“Before the Big Bang, there was nothing” is a syntactically correct but meaningless sentence, just like the sentence, “North of the North Pole, there is nothing”. The latter sentence implies that there is a location north of the North Pole that contains emptiness, when in fact, “north of the North Pole” is not a valid concept. Same goes for “before the Big Bang”.
Well, at least in the standard Big Bang cosmology. There are alternatives (e.g., bouncing cosmologies, eternal inflation) in which the Big Bang is not a singularity, just a moment in time when the universe was very hot and very dense, and it was preceded by something like a pre-inflationary state (in the case of eternal inflation) or a contracting phase (in the case of a “bounce”). But in these cases, “before the Big Bang,” there were lots of things—an entire universe in fact, quite different from our own but full of
However, those models also predict that the rate of expansion of the universe should be slowing down as the overall mass density of the universe decreases, when in fact, our observations show that this expansion is accelerating. The models also predict a more homogeneous universe than we have been able to observe. Lastly, observations of galaxies lead to conclusions that the gravitation observed is greater than can be accounted for by observable matter. And we’re talking about orders of magnitude differences, not statistical error.
This leads to the conclusion that there’s more to what we thought was the “observable” universe than we can actually observe, and that something other than the four classical fundamental forces governs the expansion universe. That supposed something is referred to as dark energy, which we have found evidence to support in the cosmological background radiation of the universe.
Models using dark energy as the driver of universal expansion, while they predict a rapid expansion overcoming gravity beginning somewhere around what we classically know as t=0 and also faithfully follow the currently observed acceleration of expansion, do not predict a convergence of all matter to a zero-volume space at that point. Instead, they show that at what we might call t=0 (the point just before expansion really ballooned), the universe already had a nonzero volume and asymptotically approaches a zero volume as t continues arbitrarily far before t=0, which effectively means there may never have been “nothing”.
On top of that, because we can’t determine a definite point of zero volume, it’s not correct to say that the universe was ever small; it was, at one point, merely very dense, so much so that prior to the Planck Epoch, all models of what the universe was like broke down because the universe was so hot that nothing but energy itself could exist, and at least so dense that multiple instances of whatever makes up the universe at the very lowest level would be crammed into a space smaller than we would ever be able to reliably measure. The universe could still have been effectively infinite in volume; there’s just more in a unit volume of the universe at this state than we can measure, and so before this time, any expansion would appear to result in the creation of something from nothing. It doesn’t; it simply results in more energy than we can measure being emitted from a smaller volume than we can measure.
In addition, our inability to observe anything for which light has not yet reached us means we can’t see all of the universe, and we may never if parts of it are expanding away from us faster than light can travel. So, we don’t know how big the universe is now, so we can’t do more than take an extraordinarily wild guess
how much matter is in the entire universe?
At any rate, it is impossible for us to do more than theorize about what the universe might have looked like at or very near t = 0. Before the end of the Grand Unification Epoch at 1E-36 seconds, the properties that define matter and even energy as we know it are meaningless, so no tool we could ever conceive of could possibly exist within the universe to observe it before this time.
It’s also believed impossible to simulate the creation of the universe at any smaller scale within our universe (because the universe is spacetime, so anything we can observe happens inside our already-existing spacetime) or to ever leave our universe and observe it from outside. So, it’s possible, and may be likely, that we will never really know what the very early universe was like and thus its origins.
We don’t know about what, if anything, was before the Big Bang. Of course, this doesn’t stop people from speculating and sounding like they know.
There is really good evidence for the Big Bang in the form of what is left lying around in the universe and what that stuff is doing. We can be confident that the universe was once extremely compressed and extremely energetic and that after the Big Bang the universe developed in a way that is consistent with known physics. This shouldn’t be a surprise because “known physics” is modelled on the observed universe.
The problem is that when you try to work back to back in time to the instant of the Big Bang, the physics gets confusing. When physicists find they are in this kind of muddle, the usual strategy is to gather data and then find equations and models that match the data. Unfortunately, all the data available comes from this universe and in the time period after the Big Bang. We’re stuck! It’s like trying to build a car using a cake recipe or something. If we had just one reliable observation from before the Big Bang (if there was anything) or from another universe (if there are any), that would be incredibly illuminating and provide enormous guidance to physics, but there appears to be nothing available, and there is probably no hope of ever getting any of the data we really require.
in this situation, physicists have to make stuff up. They don’t make up random stories (like the universe was vomited up by a giant tortoise, or something) but try to form models that are consistent with what they think are deeper underlying principles of physics. Unfortunately, no one actually knows what these deeper underlying physics principles are either. We have to make a guess about that too.
The universe from nothing is one such idea. Or more correctly, one “group” of ideas: most of these speculations come in multiple versions and may overlap with other speculative models. The general idea is that that there is a background vacuum realm that is even more empty than empty space. It doesn’t even have special dimensions and maybe not even time. This is basically impossible to visualize; you just have to believe it or not. What this proto-space does have—or is assumed to have—is quantum fluctuations, a little like the quantum fluctuations in the “empty” space in our universe that can produce random particles. Here-and-there, every now-and-then—whatever that means in realm with no space and maybe no time—a tiny little bit of real space is created by quantum fluctuations. If this bit of space is too small, it might just disappear, but if it has a critical size, it grows in a kind of wild runaway process into a universe, aka a Big Bang. The energy of the Big Bang is provided by the gravitational potential energy of the new space itself (I believe).
Is there any evidence for this? Nothing, or almost nothing. There is just one key bit of evidence: our universe has not been around forever; it or at least the current form of it, did start somehow, about 14 billion years ago.
This is just one possible model out of many. It has a bit of inner logic but it has no real evidence and isn’t even fully worked out. No one has seen the proto-vacuum; it is highly speculative. We just know that the universe exists and we guess there is some kind of cause, even if it is just a random fluctuation. Hopefully someday some one will come up with a model that fits all known observations and is internally self-consistent, plus is simple enough and doesn’t have too many arbitrary elements, but we aren’t there yet. We have a bunch of partially worked-through speculations and physicists chatting about them in their tea rooms.
But ‘nothing’ is a subtle and complex idea, and the naïve (new, inexperienced) views of it that you or I may have are also naïve in the sense of over-simplistic, or just plain wrong. But we can still say quite a bit about nothing, and in particular nothing that some people think might have been the start of things. And to look at that, let’s
… (more)Well, at least in the standard Big Bang cosmology. There are alternatives (e.g., bouncing cosmologies, eternal inflation) in which the Big Bang is not a singularity, just a moment in time when the universe was very hot and very dense, and it was preceded by something like a pre-inflationary state (in the case of eternal inflation) or a contracting phase (with a “bounce”). But in these cases, “before the Big Bang,” there were lots of things—an entire universe in fact, quite different from our own but full of “stuff” nonetheless. Not “nothing”.
However, those models also predict that the rate of expansion of the universe should be slowing down as the overall mass density of the universe decreases, when in fact, our observations show that this expansion is accelerating. The models also predict a more homogeneous universe than we have been able to observe. Lastly, observations of galaxies lead to conclusions that the gravitation observed is greater than can be accounted for by observable matter. And we’re talking about orders of magnitude differences, not statistical error.
This leads to the conclusion that there’s more to what we thought was the “observable” universe than we can actually observe, and that something other than the four classical fundamental forces governs the expansion universe. That supposed something is referred to as dark energy, which we have found evidence to support in the cosmological background radiation of the universe.
Models using dark energy as the driver of universal expansion, while they predict a rapid expansion overcoming gravity beginning somewhere around what we classically know as t=0 and also faithfully follow the currently observed acceleration of expansion, do not predict a convergence of all matter to a zero-volume space at that point. Instead, they show that at what we might call t=0 (the point just before expansion really ballooned), the universe already had a nonzero volume and asymptotically approaches a zero volume as t continues arbitrarily far before t=0, which effectively means there may never have been “nothing”.
On top of that, because we can’t determine a definite point of zero volume, it’s not necessarily correct to say that the universe was ever very small; it was, at one point, merely very dense, so much so that prior to the Planck Epoch, all models of what the universe was like broke down because the universe was so hot that nothing but energy itself could exist, and at least so dense that multiple instances of whatever makes up the universe at the very lowest level would be crammed into a space smaller than we would ever be able to reliably measure. The universe could still have been effectively infinite in volume; there’s just more in a unit volume of the universe at this state than we can measure, and so before this time, any expansion would appear to result in the creation of something from nothing. It doesn’t; it simply results in more energy than we can measure being emitted from a smaller volume than we can measure.
In addition, our inability to observe anything for which light has not yet reached us means we can’t see all of the universe, and we may never be able to if parts of it are expanding away from us faster than light can travel. So, we don’t know how big the universe is now, so we can’t do more than take an extraordinarily wild guess as to how much matter is in the entire universe.
At any rate, it is impossible for us to do more than theorize about what the universe might have looked like at or very near t = 0. Before the end of the Grand Unification Epoch at 1E-36 seconds, the properties that define matter and even energy as we know it are meaningless, so no tool we could ever conceive of could possibly exist within the universe to observe it before this time.
It’s also believed impossible to simulate the creation of the universe at any smaller scale within our universe (because the universe is spacetime, so anything we can observe happens inside our already-existing spacetime) or to ever leave our universe and observe it from outside. So, it’s possible, and may be likely, that we will never really know what the very early universe was like and thus its origins.
Is Andrei Linde’s theory of chaotic inflation compatible with our observable universe, which appears flat and possibly infinite?
Chaotic inflation is usually taken as implying eternal inflation. The Penrose diagram for an eternally expanding (inflating) universe (very like the old Steady State model, in some ways) looks like the lower half of a diamond, where the flat top is the infinite future and the lower vertex is the infinite past.
Quantum physics begins when we take some equations from classical physics, play with them a little, and come up with equations that have, besides the classical solutions, also solutions that make absolutely no freaking sense in a classical context. And then we say that these solutions nonetheless describe reality.
Remember that famous line from the movie The Matrix: “There is no spoon”? It’s really like that. There is no (classical) electron path. There is no electron position. Or momentum
So, totally separate force that you just don’t normally get taught about in high school. Gravity and electromagnetism are the “common forces” that affect our day-to-day lives, but the strong and weak nuclear forces are important as well. They just operate on very short distances.
Einstein’s now-widely accepted photon theory, precursor to his general relativity theory, states that light is packaged into “quanta” that have particle-like properties (later experiments would show a “wave-particle duality” of light and certain other very small massive particles). In the case of collisions with matter, light tends to behave more particle-like. We know that the atoms that make up matter are actually a lot of empty space due to electromagnetic forces separating atomic nuclei from each other. When light encounters a solid material, a nonzero amount of it will pass right through (though that amount may not be detectable by the human eye). The amount that passes through depends on the density of the material; the more tightly the atoms of the material are packed, the less likely a photon will get through without any collisions.
A half-silvered mirror places a thin, translucent layer of a normally highly reflective material like metal over a normally transparent material like glass. While glass is relatively high-density, the properties of the silica material it’s made of allow for the transmission of light by capturing and releasing photons along the same vector (or very near so), so it slows but does not stop or scatter visible light (glass does block UV, but that’s another question). The silver, however, will reflect light, capturing and releasing it at a very high ”refraction angle” compared to glass’s very low one. So, whether the photon is reflected by the silver or refracted through the glass of the mirror depends on what that photon hits first: silver or silica. The principles behind quantum theory state that it is impossible to predict exactly what material each photon will hit first, and thus, it is a fundamentally random event; we can use probability and the Law of Large Numbers to predict percentages of light reflection and transmission, but tracing any single photon’s path through spacetime is impossible.
In any case, the important lesson to remember is that the initial singularity is a moment in time that is not part of this universe; only subsequent moments are. Kind of like the set of all real numbers that are greater than 0. This set includes.
There is really good evidence for the Big Bang in the form of what is left lying around in the universe and what that stuff is doing. We can be confident that the universe was once extremely compressed and extremely energetic and that after the Big Bang the universe developed in a way that is consistent with known physics. This shouldn’t be a surprise because “known physics” is modelled on the observed universe.
The problem is that when you try to work back to back in time to the instant of the Big Bang, the physics gets confusing. When physicists find they are in this kind of muddle, the usual strategy is to gather data and then find equations and models that match the data. Unfortunately, all the data available comes from this universe and in the time period after the Big Bang. We’re stuck! It’s like trying to build a car using a cake recipe or something. If we had just one reliable observation from before the Big Bang (if there was anything) or from another universe (if there are any), that would be incredibly illuminating and provide enormous guidance to physics, but there appears to be nothing available, and there is probably no hope of ever getting any of the data we really require.
in this situation, physicists have to make stuff up. They don’t make up random stories (like the universe was vomited up by a giant tortoise, or something) but try to form models that are consistent with what they think are deeper underlying principles of physics. Unfortunately, no one actually knows what these deeper underlying physics principles are either. We have to make a guess about that too.
The universe from nothing is one such idea. Or more correctly, one “group” of ideas: most of these speculations come in multiple versions and may overlap with other speculative models. The general idea is that that there is a background vacuum realm that is even more empty than empty space. It doesn’t even have SPECIAL dimensions and maybe not even time. This is basically impossible; you just have to kind of believe it or not. What this proto-space does have—or is assumed to have—is quantum fluctuations, a little like the quantum fluctuations in the “empty” space in our universe that can produce random particles. Here-and-there, every now-and-then—whatever that means in realm with no space and maybe no time—a tiny little of real space is created by quantum fluctuations. If this bit of space is too small, it might just disappear, but if it has a critical size, it grows in a kind of wild runaway process into a universe, aka a Big Bang. The energy of the Big Bang is provided by the gravitational potential energy of the new space itself (I believe).
Is there any evidence for this? Nothing, or almost nothing. There is just one key bit of evidence: our universe has not been around forever; it or at least the current form of it, did start somehow, about 14 billion years ago.
This is just one model out of many. It has a bit of inner logic, but it has no real evidence and isn’t even fully worked out. No one has seen the proto-vacuum; it is highly speculative. We just know that the universe exists and we guess there is some kind of cause, even if it is just a random fluctuation. Hopefully, someday someone will come up with a model that fits all known observations and is internally self-consistent, plus is simple enough and doesn’t have too many arbitrary elements, but we aren’t there yet
