What do you think about the Big Bang?

[Beyond]

I thought we just got through having a conversation that the matter and energy were already here before the Big Bang arrived to change it?

[Beyond]

So, you are saying that the prevailing theory is that the whole universe came into being about the way it is now, in under 1 second? Or, in the blink of an eye? Where do you find anything even remotely close to that speed that brings anything into being?

[bystander]

The whole universe, as it is now, took about 13.7 billion years to form. The first stars and galaxies didn't form until about 400 million years after the big bang (the advent of reionization). A universe we might recognize wasn't until after reionization, about 1 billion years after the BB. The farthest thing we can see (the Cosmic Microwave Background Radiation (CMB)) is from about 377,000 years after the BB.

Schematic timeline of the universe, depicting reionization's place in cosmic history. (NASA/JPL-Caltech)

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[Beta]

The Big Bang event is defined as the moment that the Universe came into being... and time itself was created with the Big Bang.

I beg to differ (or at least doubt). The Big Bang event is a something we extrapolate from present observations, something that happened roughly 13.5 bya, and we don't yet understand it completely. Someday we'll have better theories, and maybe they'll describe how time began then and how inflation followed from that and so on. But maybe they'll tell us something different like, I don't know, a small cold mostly empty expanse of space that was there for at least hundred trillion years before it fractured and produced lots of energy and inflation and so on (I'm making this up). In that case it would still be perfectly reasonable to call that event "the Big Bang" (and to wonder how the small cold space began, if it ever did).

I agree that it's wrong to talk glibly about "before the Big Bang", but I think it's also unjustified to claim with certainty that there was no such thing.

[bystander]

You can beg to differ all you want, according to the BBT, space and time came into being at t₀, the beginning of the Big Bang Timeline. Anything before is in the realm of cosmogony and beyond the scope of this forum.

[Chris Peterson]

I thought we just got through having a conversation that the matter and energy were already here before the Big Bang arrived to change it?

I didn't have that conversation. I'm just pointing out that the idea is not one that most cosmologists would agree with, and in this forum it hasn't been presented as a scientific theory.

[Chris Peterson]

I agree that it's wrong to talk glibly about "before the Big Bang", but I think it's also unjustified to claim with certainty that there was no such thing.

It is pretty certain that there was no "before" in any usual sense of that word. Whether our Universe came into being as an effect of something outside it is a complex question, that may be unanswerable. That cause-and-effect scenario doesn't require that time existed, so "before" becomes an abstract mathematical construct.

[Beyond]

UREKA! - (i think) -- This is an "ask Astronomy questions forum". Astronomy deals with things the way they are - and not how they got that way.
Cosmotology deals with how things came into being and not how they are now.
So if you are inquireing about how things came into being you are out of bounds of this Astronomy forum.
I never realized that before. Of course I'll have to wait for a response or two to see if i agree with my assessment of the situation.

[bystander]

Astronomy is the study of the physical universe beyond the Earth's atmosphere, including the process of mapping locations and properties of the matter and radiation in the universe. Astrophysics is the branch of astronomy or physics that deals with the physical properties of celestial bodies and with the interaction between matter and radiation in celestial bodies and in the space between them. Cosmology is the study of the physical universe, its structure, dynamics, origin and evolution, and fate. All fall within the scope of this forum.

Cosmogony is any philosophical theory concerning the coming into existence or creation of the universe, or about how reality came to be. The term refers to creation theories of the universe. There are no scientific inquires or physical models that can explain the earliest moments of the existence of the universe. This, then, is beyond the scope of this forum.

Cosmogony can be distinguished from cosmology which studies the universe at large and throughout its existence, and which technically does not inquire directly into the source of its origins. There is some ambiguity between the two terms; for example, the cosmological argument from theology regarding the existence of God is technically an appeal to cosmogonical rather than cosmological ideas. In practice, there is a scientific distinction between cosmological and cosmogonical ideas. Physical cosmology is the science that attempts to explain all observations relevant to the development and characteristics of the universe as a whole. Questions regarding why the universe behaves in such a way have been described by physicists and cosmologists as being extra-scientific, though speculations are made from a variety of perspectives that include extrapolation of scientific theories to untested regimes and philosophical or religious ideas.

Cosmetology is learned at beauty school and has nothing to do with anything in this forum.

[Beyond]

Ok, disregarding the fact i did not spell correctly what i was thinking (cosmology), then every term of science used to describe any thing this side of Tee-zero(i can't type it with this keyboard so i have to spell it)is acceptable and everything on the other side of Tee-zero (cosmogony) is out of the bounds of this forum at least until such time as someone reputable comes up with some kind of model for it. Did i get it right?

Now, how about realms and dimentions? Do they fit here?

[bystander]

This forum deals with main-stream science, anything else is outside the scope of the forum. Idle speculation and honest questions about possibilities are fine, but if you wish to espouse some alternative theory, you had better be prepared to defend with rigorous evidence and facts complete with reputable sources. Although we do joke around in this forum, we are serious about our science and excessive tomfoolery or trolling is stringently discouraged.

[Chris Peterson]

UREKA! - (i think) -- This is an "ask Astronomy questions forum". Astronomy deals with things the way they are - and not how they got that way.
Cosmotology deals with how things came into being and not how they are now.
So if you are inquireing about how things came into being you are out of bounds of this Astronomy forum.
I never realized that before. Of course I'll have to wait for a response or two to see if i agree with my assessment of the situation.

Cosmology is a branch of astronomy. Like all science, it deals with how things are, and how things got that way. There is nothing wrong with posing the question "what caused the Big Bang". The best scientific answer is that the question cannot be answered, may not be answerable, and may not even be a scientific question. There are people trying to formulate mechanisms by which a sort of hyperuniverse can spawn a universe, but for the most part these are very speculative ideas, which are largely untestable and are therefore largely unscientific.

[Ann]

Chris wrote:

There is nothing wrong with posing the question "what caused the Big Bang".

Good to hear, Chris!

The best scientific answer is that the question cannot be answered, may not be answerable, and may not even be a scientific question.

I get that, too. But scientists don't always agree among themselves. (Never fear,though, Chris, I'm not a fan of the wildest speculative theories about the cosmos. Having grown up among religious fundamentalists who told me that the world was coming to an end any day now took away most of my appetite for dramatic unproven theories.)

I'm going to ask another "honest question" which has probably been asked before. Inflation, the inflation that happened almost instantly after the actual Big Bang, is unexplained, as far as I can understand. Inflation has been "added" to the theory about the Big Bang because it answers many questions about the universe, like how the observable universe can be so uniform and isotropic. But as far as I can understand, inflation has been inferred from the appearance of the universe, not from any mathematical theories of how the Big bang "ought to" enfold. So science can't say why inflation happened.

Recently, the apparent acceleration of the universe dropped the latest bombshell in astronomers' laps. I followed astronomy throughout the nineties, and I vividly remember that astronomers speculated on just how much the expansion of the universe was slowing down. When it was found to accelerate, most astronomers were absolutely dumbstruck, and many refused to accept the findings.

So my point is that we have a case of early inflation that astronomy can't really explain, and now we have a case of universal accelearation that no one can really explain. Is there a connection between the two? I think I know what you are going to answer, Chris: no, there is no connection because the two forms of increasing expansion of the universe are so fundamentally different. And I guess I realize that myself. Nevertheless, there seems to be an underlying principle here, saying that the universe might increase the amount of its expansion for no reason that science can readily explain. To me, that points to some sort of connection.

Ann

[Chris Peterson]

I'm going to ask another "honest question" which has probably been asked before. Inflation, the inflation that happened almost instantly after the actual Big Bang, is unexplained, as far as I can understand.

That's not true. In fact, there are explanations for inflation- scientific theories that are testable. It would be far better to say that the cause of inflation is still under investigation, and that no single idea has been tested sufficiently to make anybody confident that the process is well understood. But that doesn't mean that most people don't think we're on the right track towards an understanding. Inflation does fit in with the mathematics used to describe the early Universe.

Recently, the apparent acceleration of the universe dropped the latest bombshell in astronomers' laps. I followed astronomy throughout the nineties, and I vividly remember that astronomers speculated on just how much the expansion of the universe was slowing down. When it was found to accelerate, most astronomers were absolutely dumbstruck, and many refused to accept the findings.

Again, a mischaracterization. The result was unexpected, and astronomers were quite properly skeptical of the initial findings. Once the observations were confirmed, however, very few refused to accept them. And the shift in accepted understanding occurred very rapidly.

So my point is that we have a case of early inflation that astronomy can't really explain, and now we have a case of universal accelearation that no one can really explain.

Dark energy explains the acceleration. And dark energy fits very nicely into the Big Bang cosmology. So again, I'd quibble with your suggestion of this being unexplained. That is very different from not fully understood.

Is there a connection between the two?

There may well be. Both inflation and accelerated expansion are posited to be caused by negative pressure effects of vacuum energy. Whether the mechanism is the same, or even the energy, we aren't going to know until more theoretical work is in place, and more observational evidence as well.

[Henning Makholm]

So my point is that we have a case of early inflation that astronomy can't really explain, and now we have a case of universal accelearation that no one can really explain.

Dark energy explains the acceleration. And dark energy fits very nicely into the Big Bang cosmology. So again, I'd quibble with your suggestion of this being unexplained. That is very different from not fully understood.

What happened to the "cosmological constant" that was supposed to be the canonical cause of an accelerating universe back when I learned GR? At some point there was talk about evidence for it being positive, but shortly thereafter everybody started talking about "dark energy" instead. I took that to mean that some reason had been found that it couldn't be the cosmological constant, and instead the observed effect had, for ease of reference, been given the placeholder name "dark energy" until a good explanation had been found. So, if an explanation has been found, why is we-don't-know-what-this-is sounding placeholder still being used?

Or was it, in fact, just that somebody decided that "cosmological constant" did not sound sufficiently mystical and therefore invented a new name for the exact same term in the equation? If so, the new name appears to be distinctly inferior to me. It suggests that there is something tangible in spacetime that does something, rather than just a different connection between contents and curvature that one might otherwise have expected. Not to speak of the confusion with "dark matter" it invites.

[Chris Peterson]

What happened to the "cosmological constant" that was supposed to be the canonical cause of an accelerating universe back when I learned GR?

Dark energy is essentially the same as the cosmological constant, with most standard theory variants.

[bystander]

Revised theory of gravity doesn't predict a Big Bang
PhysOrg | General Physics | 12 July 2010

The Big Bang theory has formed the basis of our understanding of the universe's origins since it was first proposed in 1927 by Georges Lemaitre. And for good reason: the theory is supported by scientists' latest observations and experiments, and is based on Einstein's widely accepted theory of general relativity. But scientists are always on the lookout for any evidence that might suggest an alternative to the Big Bang. The latest in this area of research comes from astrophysicists Maximo Banados and Pedro Ferreira, who have resurrected a theory of gravity from the early 20th century and discovered that a modified version of the theory may hold some surprises.

In a recent study published in Physical Review Letters, Banados and Ferreira have reconsidered the theory of gravity proposed by Arthur Eddington, a contemporary of Einstein. Eddington is perhaps best known for his trip to the Island of Principe on the west coast of Africa in 1919, where during a solar eclipse he observed that the Sun's gravity does indeed bend starlight, providing one of the earliest confirmations of general relativity.

Although Eddington played a significant role in developing general relativity, during the following decades he became more interested in finding a theory to unify gravity and quantum mechanics - a task that is still being studied today. In 1924, Eddington proposed a new “gravitational action” as an alternative to the Einstein-Hilbert action, which could serve as an alternative starting point to general relativity. In astrophysics, a gravitational action is the mechanism that describes how gravity can emerge from space-time being curved by matter and energy. However, Eddington’s theory of gravity only worked for empty space and didn’t include any source of energy such as matter, making it an incomplete theory.

Since Eddington’s proposal, scientists have attempted various ways of including matter into the theory, although they have run into problems. In this study, Banados and Ferreira have tried a new way to extend the theory to include matter by using a gravitational action called the Born-Infeld action.

In their analysis, the scientists found that a key characteristic of Eddington’s revised theory of gravity is that it reproduces Einstein gravity precisely in the vacuum conditions (with no matter), but it produces new effects when matter is added. Due to this characteristic, the revised theory has implications especially for high-density regions, such as in the very early Universe or within a black hole. For instance, the theory predicts a maximum density of homogeneous and isotropic space-time, which could have implications for black hole formation.

More intriguingly, the theory could lead to an entirely new view of the Universe that doesn't include a Big Bang. In Big Bang theory, the state of the Universe is a singularity in early times, meaning that the Universe was once infinitely small. However, Eddington’s revised theory requires a minimum length of space-time at early times, which means that the Universe could not have been a singularity. The theory predicts that, depending on the Universe’s initial density, it may have loitered for a long time at a relatively small size before growing large enough to be controlled by standard cosmological evolution. Another possibility, depending on the initial conditions, is that the Universe could have undergone a bounce, resulting from the collapse of a previous Universe. Any kind of singularity-free Universe would solve the singularity problem that has bothered scientists about general relativity, since a singularity cannot be mathematically defined. ...

Eddington’s Theory of Gravity and Its Progeny

• Physical Review Letters 105 011101 (02 July 2010) | DOI: 10.1103/PhysRevLett.105.011101

[The Code]

The whole universe, as it is now, took about 13.7 billion years to form. The first stars and galaxies didn't form until about 400 million years after the big bang (the advent of reionization). A universe we might recognize wasn't until after reionization, about 1 billion years after the BB. The farthest thing we can see (the Cosmic Microwave Background Radiation (CMB)) is from about 377,000 years after the BB.

Schematic timeline of the universe, depicting reionization's place in cosmic history. (NASA/JPL-Caltech)

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Whats That? 8.6 Billion years, With no expansion? Now that,s interesting.

tc

[bystander]

Whats That? 8.6 Billion years, With no expansion? Now that,s interesting.

Where do you get that? It's been expanding all along. Now, the rate of expansion is increasing.

[swainy]

Whats That? 8.6 Billion years, With no expansion? Now that,s interesting.

Where do you get that? It's been expanding all along. Now, the rate of expansion is increasing.

Does that mean the graph is misleading? Looks like 2 vertical lines, to me. From 400 million to 9 billion.

tc

[bystander]

Does that mean the graph is misleading? Looks like 2 vertical lines, to me. From 400 million to 9 billion.

I think you are trying to read something into the illustration that isn't there. I'm fairly certain there was never an intent to imply expansion was at a standstill.

[Chris Peterson]

I think you are trying to read something into the illustration that isn't there. I'm fairly certain there was never an intent to imply expansion was at a standstill.

Certainly not. Expansion has been at a near constant rate since shortly after the inflationary period, and even as the effects of dark energy have begun to increase expansion in the last few billion years, the actual rate has only slightly increased. That's why we can quite accurately determine the distance to objects by treating Hubble's constant as a constant (which in fact, it is not).

[swainy]

Does that mean the graph is misleading? Looks like 2 vertical lines, to me. From 400 million to 9 billion.

I think you are trying to read something into the illustration that isn't there. I'm fairly certain there was never an intent to imply expansion was at a standstill.

Hence the wink. Quite interesting, though, 8.6 billion years steady rate expansion, then BAM! What changed?

tc

[Chris Peterson]

Hence the wink. Quite interesting, though, 8.6 billion years steady rate expansion, then BAM! What changed?

You're still reading too much into the illustration. There was no "BAM". Since inflation, dark energy has been increasing the expansion rate. But gravity is stronger, so the effects of dark energy are very hard to see until the Universe expanded enough that the average density dropped, shifting the balance a bit away from gravity and towards dark energy. The illustration greatly exaggerates the change in expansion rate over the last 4 billion years. Instead of a bell, the image should look more like a pair of cones, a very flat one before inflation, and a very steep one after, with just the barest amount of flaring now showing up.

[swainy]

The illustration greatly exaggerates the change in expansion rate over the last 4 billion years. Instead of a bell, the image should look more like a pair of cones, a very flat one before inflation, and a very steep one after, with just the barest amount of flaring now showing up.

I did ask if the Graph was misleading. Thanks Chris. JD

tc