Why does the universe have to have a beginning?

[Vexa]

If energy cannot be created or destroyed, that means all the energy that ever was and ever will be already exists. Wouldn't this mean that the universe has always existed? ..in one form or another. Everything that dies here on Earth goes back to the planet and new life is created. The universe could have this cycle as well.

I guess it's difficult for us to imagine something not having a beginning.

 

[payumooli]

When we look at the Cosmic Microwave background or CMB radiation. We see a uniform pattern. From this we deduced that there was a period when the universe was hot and dense.
When we see the distant galaxies we see that they are moving away from us according to hubbles law. We can use either general relativity or Newtonian gravity to explain the expansion of the universe as a function of time.
Now when we run the time backward we can reach the point of CMB where our equations still predict the observation.
But there is no way for us to know the state of the universe before the CMB so we contemplate various possible explanations which wll make the equations elegant.

 

[Chalnoth]

If energy cannot be created or destroyed, that means all the energy that ever was and ever will be already exists.

This is a good essay on the subject:
http://math.ucr.edu/home/baez/physics/Relativity/GR/energy_gr.html

The basic gist is this: when taking into account the nature of General Relativity, the conservation of energy becomes much more subtle. In the typical formulation of GR, energy is simply not a conserved quantity. It doesn't change in specific situations, but in general energy tends to change quite a lot.

But it doesn't change willy-nilly. General Relativity does have its own conservation laws. And it is possible to use this fact to develop a concept of gravitational potential energy (this is known as the Hamiltonian formalism). If you do this, and apply it to a universe like our own, you get that the total energy in all matter plus the total gravitational potential energy is identically equal to zero (provided the spatial curvature is positive, even if only a little bit). This means that you can create all the universes you want, as it requires no energy whatsoever to do so.

 

[alpha2cen]

Total Universe Energy = Dark Energy + Dark matter(convert to matter) X C^2 + matter X C^2 + 4K * (hole universe specific heat)

Energy conversion law

Initial Energy = Current Energy.

Assumption

At the beginning

Total Static Energy => Entropy Increase

 

[Chalnoth]

Total Universe Energy = Dark Energy + Dark matter(convert to matter) X C^2 + matter X C^2 + 4K * (hole universe specific heat)

Energy conversion law

Initial Energy = Current Energy.

Assumption

At the beginning

Total Static Energy => Entropy Increase

Energy isn't conserved in this sense in an expanding universe.

 

[alpha2cen]

Total Universe Energy = Dark Energy +Dark Matter(convert to matter mass) X C^2 +matter mass X C^2 + 4K X (hole universe specific heat capacity)

Energy conversion law

System ---current universe

Assumption Initial Energy =0
Initial Energy =Current Universe Energy
0 = Current Universe Energy

Assumption Initial Energy NOT 0
Initial Energy =Current Universe Energy
At the beginning static energy => entropy increase

System --- current universe +other universe
Initial Energy =Current Universe Energy + Other Universe Energy
0 = Current Universe Energy + Other Universe Energy
Current Universe Energy = - Other Universe Energy

 

[bcrowell]

Now when we run the time backward we can reach the point of CMB where our equations still predict the observation.
But there is no way for us to know the state of the universe before the CMB so we contemplate various possible explanations which wll make the equations elegant.

This is incorrect. The CMB is a physical phenomenon, not a name for a time. It exists today, and it also existed in the earlier universe. The CMB comes frome the surface of last scattering, which existed at a definite time, about 400,000 years after the big bang. This time is not the earliest to which we can extrapolate using the known laws of physics. We can extrapolate much, much earlier than that before running into conditions under which we don't know the laws of physics. We don't really know about inflation, but inflation would have been around t=10^-32 s. None of this has anything to do with making equations elegant.

 

[Chronos]

In bouncing cosmological models, there is no big bang event. In such models the universe had no 'beginning'.

 

[daniel rey m.]

Vexa,


Is that an idea of your own or is it something that's been going around? That reasoning concerning the Universe seems to be unassailable. It's a brilliant insight. It cuts the Gordian Knot. There's no need for mathematical calculations anymore. The law of conservation is proof that the Universe is eternal and it shows that the Big Bang Theory is mistaken.

As though that weren't enough, there are alternate explanations for the spurious proofs of that theory (the redshift of absorption lines on a spectrum, the CMBR, Olber's Paradox [nights are dark rather than dazzling], the images of a more violent, supposedly "younger" Universe on the edge of its most distant visible parts).

 

[elisir]

Vexa,

Physics is not to describe the infinite past or future of things. We never and ever can infinitely extrapolate a theory which we know only is capable of approximately describing the universe, to its infinite past or future. So the questions of beginning or end simply relies outside the realm of physics. Ask this question from Mullah in Qom, or priests in Vatican. But I assure you no one can give you a satisfactory answer as long as you do not cheat yourself.

 

[Chalnoth]

Is that an idea of your own or is it something that's been going around? That reasoning concerning the Universe seems to be unassailable. It's a brilliant insight. It cuts the Gordian Knot. There's no need for mathematical calculations anymore.

No need for mathematical calculations? There really isn't any better indication that it's just plain wrong. If there is no need for mathematical calculations, then there is no possibility of comparing with experiment.

The law of conservation is proof that the Universe is eternal and it shows that the Big Bang Theory is mistaken.

Which law of conservation, specifically? Because conservation laws stem from symmetries of the universe. They are not absolute, but dependent upon these underlying symmetries. See theorem[/url].

As though that weren't enough, there are alternate explanations for the spurious proofs of that theory (the redshift of absorption lines on a spectrum, the CMBR, Olber's Paradox [nights are dark rather than dazzling], the images of a more violent, supposedly "younger" Universe on the edge of its most distant visible parts).

Uhhh, those are only the most basic, simple arguments for the big bang theory. The actual arguments used within cosmology include vastly more data. This is a good overview of the evidence available today:
http://www.talkorigins.org/faqs/astronomy/bigbang.html

 

[daniel rey m.]

Chalnoth,

Vexa mentions only one law of conservation…or did he ever talk about electric charge, linear and angular momentum, number of baryons, number of leptons, strangeness, spin….

"No need for mathematical calculations? There really isn't any better indication that it's just plain wrong. If there is no need for mathematical calculations, then there is no possibility of comparing with experiment." Plain logic can lead to inevitable conclusions about the nature of reality, too.

That's how the Greek thinkers discovered that matter is made up of invisible particles, and they didn't do it with artifacts and computations, but just by observing. They saw that the stones of their paths wore away but there were no residues to be seen. They concluded that tiny parts of them had been removed. They also saw how the wind was able to push a heavy ship forward, or break a branch, and that one could smell things at a distance, but nothing was seen in the air, so the only explanation was that there had to be invisible particles in the air that pushed things or went through the nose.

You're throwing at me "a good overview of the evidence" that says it didn't all start at a point, that it was more than that, but that they don't know how much more. To begin with, since a point is something without the least magnitude, anything that's not a point is infinitely large as compared to the nothingness that is a point.

Second, they never mention time. They believe that the Thing was apparently always there until it decided to expand. That's not what classical Bigbangers say: what they say is that time and space came into being as soon as the expansion began, so that it makes no sense to ask what came before. This is suspiciously similar to Kant's concept of "empty time".

Then space magically kept expanding into nothing since anything apart from expanding space is nonexistent, so that it makes no sense to ask what lies beyond the growing frontier. This is a logical impossibility since anything spatial must necessarily be contained within something that is also spatial, rather than by nothingness, which does not exist, by virtue of its own definition.

The root of the problem is that the mind can't grasp the idea of endless space and time and will attempt to place limits. They've gone back to the time of the Greeks, whose Universe was a closed sphere beyond which there was nothing at all (neither space nor matter).
***

 

[Chalnoth]

Vexa mentions only one law of conservation…or did he ever talk about electric charge, linear and angular momentum, number of baryons, number of leptons, strangeness, spin….

What, energy? That's not a conserved quantity in General Relativity.

Plain logic can lead to inevitable conclusions about the nature of reality, too.

Nope. In fact, there aren't any inevitable conclusions about reality. That's impossible. Plato's school was completely and utterly wrong on this point.

All of our conclusions about reality are necessarily contingent upon observation. And performing observations inevitably means doing some math. Sorry, but that's the way it works.

You're throwing at me "a good overview of the evidence" that says it didn't all start at a point, that it was more than that, but that they don't know how much more. To begin with, since a point is something without the least magnitude, anything that's not a point is infinitely large as compared to the nothingness that is a point.

What does that have to do with anything? The big bang theory doesn't include the behavior at the beginning. Full stop. It only describes the behavior of the universe after a certain time, and says nothing about what came before (well, technically, you can extrapolate the equations as far back as you like, but the results are nonsensical, so we artificially cut off the equations before a certain time to keep the theory sensible, assuming that there is some as yet unknown theory that accurately describes earlier times).

You have to go beyond the big bang theory to talk about the beginnings of the universe. There are many candidates, but none stick out as being particularly better than the others.

Then space magically kept expanding into nothing since anything apart from expanding space is nonexistent, so that it makes no sense to ask what lies beyond the growing frontier. This is a logical impossibility since anything spatial must necessarily be contained within something that is also spatial, rather than by nothingness, which does not exist, by virtue of its own definition.

That's not a valid conclusion. You can simply state that space-time is only defined on the manifold, and there just isn't anything beyond it. This is most easily visualized in the case of a closed manifold, where you can't talk about what lies beyond the X direction, because if you were able to travel far enough in that direction, you'd arrive back at your starting point.

The root of the problem is that the mind can't grasp the idea of endless space and time and will attempt to place limits. They've gone back to the time of the Greeks, whose Universe was a closed sphere beyond which there was nothing at all (neither space nor matter).
***

What the mind can or cannot grasp is not a problem for mathematics, fortunately. Mathematics is a crutch we can use to augment our puny brains so that we can accurately describe systems that we can't begin to understand on an intuitive level.

 

[qraal]

If energy cannot be created or destroyed, that means all the energy that ever was and ever will be already exists.

Energy can be positive or negative. Equal quantities of both mean the average is zero, but one could have infinite amounts of both regardless. Conservation Laws from thermodynamics come from observing Earth-bound systems at the micro-level. WHat they then mean at the cosmic level is entirely debatable and has been debated for over a century and a half so far.

Wouldn't this mean that the universe has always existed? ..in one form or another.

Eternal energy and universes appeal to unimaginative philosophical types who can't think outside what they know directly or can see. Kind of boring really.

Everything that dies here on Earth goes back to the planet and new life is created. The universe could have this cycle as well.

Why? Everything reproduces here too. Do Universes? Everything here evolves. Do Universes? These are dubious analogies, but have been seriously proposed from time to time. They aren't (very) scientific, but can be fun.

I guess it's difficult for us to imagine something not having a beginning.

We can't imagine our own personal beginnings except vaguely, nor can we imagine our own non-existence. But neither is excluded because imagination fails us either.

 

[LBrandt]

If energy cannot be created or destroyed, that means all the energy that ever was and ever will be already exists. Wouldn't this mean that the universe has always existed?

Regardless of whether one believes in the "big bang" or not, the above assumption makes no logical sense. The law of conservation of matter and energy to which you refer, is a physical law of THIS universe. We are not allowed to simply extrapolate and deduce that this same law would apply to a different or previous universe. On the contrary, since we know nothing of any universe but this one, we have to assume that the physical laws of THIS universe apply to THIS universe alone. As far as the "Big Bang" theory goes, all of the matter and energy that exists today was created by the event of the "Big Bang", so any discussion of physical laws of the universe must apply only to THIS universe and not to anything else.

 

[Chalnoth]

Regardless of whether one believes in the "big bang" or not, the above assumption makes no logical sense. The law of conservation of matter and energy to which you refer, is a physical law of THIS universe.

Well, no, it actually isn't. General Relativity includes no law of conservation of energy (though energy is conserved under special conditions, or if you formulate things to force it), and conservation of matter is only an approximation used in chemistry. Quantum field theory throws conservation of matter out the window.

 

[LBrandt]

Well, no, it actually isn't. General Relativity includes no law of conservation of energy (though energy is conserved under special conditions, or if you formulate things to force it), and conservation of matter is only an approximation used in chemistry. Quantum field theory throws conservation of matter out the window.

Ok, I'll accept that. But in any case, the OP's original assumption is still illogical, since it suggests that this universe must adhere to a rule that could not have existed without this universe.

 

[daniel rey m.]

Chalnoth,

"All of our conclusions about reality are necessarily contingent upon observation. And performing observations inevitably means doing some math. Sorry, but that's the way it works."

As you say, conclusions follow observations, which was how they inferred the existence of atoms in those days (B.C.), but contrary to what you say, it was a case in which, surprisingly, observing implied no mathematical reckoning, and they managed to discover the microstructure of matter, because the proof was there for all to see.

" What does that have to do with anything? The big bang theory doesn't include the behavior at the beginning."

Oh yes it does, because for Bigbangers their "singularity" IS "the Beginning". "The behavior at the beginning" is simply a Seed On Standby, a Seed In Abeyance, the Seed in the Dormant Mode, or the Universe in the Latent Phase. That Thing is behaving in a certain way: IT IS WAITING. That's where their Genesis starts. They're inventing their unique, singular Cosmic Seed and placing it somewhere, which they call Everywhere, and so the Expansion started everywhere since they deny the existence of anything apart from the Seed. What the theory omits is what caused the expansion, the Let There Be Light, the Fiat Lux. They refuse to talk about the Before (time) and the Beyond (space), and no wonder, since their imagination and their equations don't let them go that far back or afield, respectively.

Their "singularity" is a point and a point is "that which has position but no magnitude", in other words, an impossibility and strictly an ideal, mathematical object. A Belgian priest first said that in the Beginning there was the Point, and the Point expanded, and science built a new religion around this. Heretics are not burnt at the stake anymore but they're treated with scorn.

"That's not a valid conclusion. You can simply state that space-time is only defined on the manifold, and there just isn't anything beyond it."

By "simply stating" that you're decreeing nothingness into existence, which is an illegitimate leap of logic. The magical "manifold", like the "singularity", is merely a creature of the mathematical equations.

" (…) conservation of matter is only an approximation used in chemistry. Quantum field theory throws conservation of matter out the window."

…just an approximation, yes, because the loss of matter in chemical reactions (vs. NUCLEAR ditto) is infinitesimal and can be conveniently ignored, but we live in a strangely dual world. Physics has a set of rules for the macroworld and another one for the nanoworld. First you mention the Law of Conservation of Energy, then the Law of Conservation of Matter, but since matter and energy are the twin manifestations of one same thing and so are interchangeable (cp. E = mc^2) what we have is matter/energy and one law implies the other. If a theory throws one of them out the window then surely it must be a window of the house where the theory dwells temporarily, and from which it can be thrown out by the next lodger, not the window of the Universe.
***

 

[Chalnoth]

As you say, conclusions follow observations, which was how they inferred the existence of atoms in those days (B.C.), but contrary to what you say, it was a case in which, surprisingly, observing implied no mathematical reckoning, and they managed to discover the microstructure of matter, because the proof was there for all to see.

Doesn't work. The problem here is that without mathematics, you have no way of knowing how good an observation is. While it's obviously possible to reach some very limited but correct conclusions in this manner, you have no way of ensuring the validity of the result.

Even if you don't like this, I'll just point out that with math you might potentially be able to make the very limited deduction that atoms exist, but there's no way you could discover even part of the periodic table.

Oh yes it does, because for Bigbangers their "singularity" IS "the Beginning".

This is just false, though. As I said, while there is a singularity in the math, the theory doesn't include that singularity.

One way of understanding it is this: the big bang theory assumes General Relativity. But we are quite sure that General Relativity cannot be valid above the Planck density. So we cannot trust the theory in any regime where it states there is a density near or above the Planck density. And the region around the singularity is one such regime.

So the singularity is excluded from the theory, meaning the big bang theory says nothing whatsoever about any beginning of our universe.

By "simply stating" that you're decreeing nothingness into existence, which is an illegitimate leap of logic. The magical "manifold", like the "singularity", is merely a creature of the mathematical equations.

No. It's just a statement that space-time is defined on the manifold. There is no concept of "outside" the manifold to talk about. The manifold, by the way, is hardly magical, but a very specific mathematical construct.

…just an approximation, yes, because the loss of matter in chemical reactions (vs. NUCLEAR ditto) is infinitesimal and can be conveniently ignored, but we live in a strangely dual world. Physics has a set of rules for the macroworld and another one for the nanoworld. First you mention the Law of Conservation of Energy, then the Law of Conservation of Matter, but since matter and energy are the twin manifestations of one same thing and so are interchangeable (cp. E = mc^2) what we have is matter/energy and one law implies the other. If a theory throws one of them out the window then surely it must be a window of the house where the theory dwells temporarily, and from which it can be thrown out by the next lodger, not the window of the Universe.
***

But as I stated, the energy is not a conserved quantity in General Relativity. Instead, General Relativity conserves the stress-energy tensor, which includes energy density, momentum density, pressure, and twisting stresses. Conservation of the stress-energy tensor forces, under specific conditions, the energy component to not be conserved. General Relativity is still quite well-behaved, and does lead to energy conservation under many situations. But the expanding universe is not one of them.

One way this can be understood is by the fact that under General Relativity, gravitational potential energy is not considered. For example, if I have two masses that begin stationary some distance from one another, then their gravitational attraction will pull them together, giving them more and more kinetic energy. Under the typical formulation of General Relativity, this is just an example of the two masses gaining energy.

Under classical mechanics, we usually consider the kinetic energy of the particles as stemming from gravitational potential energy, so that the overall energy of the system remains the same. If we so choose, we can also define a potential energy in General Relativity. This formulation is known as the Hamiltonian formulation of GR. With this definition, energy is conserved overall, and in fact the energy of a closed universe is always identically zero. However, no matter how you describe the energy, whether using the normal formulation or the Hamiltonian one, the fact still remains that you can have a universe that changes the amount of energy in matter fields quite dramatically with time, and one which changes the amount of matter as well.

Finally, a small nitpick. The equation:
$$E=mc^2$$

is not complete. This is only the energy of a non-moving particle. The full equation is:
$$E = \gamma mc^2$$

Where $\gamma$ is the usual velocity-dependent factor in General Relativity. This means, for instance, that you can slam together two low-mass particles with very large kinetic energy, and end up with two different high-mass particles with lower kinetic energy.

 

[daniel rey m.]

" (…) while there is a singularity in the math, the theory doesn't include that singularity."

Those reckonings are not a part of the theory? The claim that it doesn't include the singularity is puzzling because the expansion implies a Square One. It had to start somewhere and that somewhere is supposed to be a phenomenon one could describe with the phrase "infinite point density". (I just coined it! Where can I apply for the ©?)

It looks like the theory conveniently and pointedly ignores what it points out as the starting point. Isn't this scientifically dishonest and irresponsible? The theory talks the talk, but does it walk the walk? It refuses to face the Chasm, the Maw of Infinitude/Eternity, like the predecessors in Ancient Greece. It gives birth to the Point, then it turns its back on the child?

"Finally, a small nitpick."

That's no nitpicking but a timely revelation. Thank you for the patience.

 

[Chalnoth]

Those reckonings are not a part of the theory? The claim that it doesn't include the singularity is puzzling because the expansion implies a Square One. It had to start somewhere and that somewhere is supposed to be a phenomenon one could describe with the phrase "infinite point density". (I just coined it! Where can I apply for the ©?)

As I said, the theory doesn't include the start.

The thing you have to realize is that nobody within science expects any of our theories to be completely, absolutely true. Instead, they all have a range of applicability. The big bang theory, for instance, is an accurate description of the behavior of our universe from the time that big bang nucleosynthesis occurred to now. It probably works well for some time before that, but as yet we can't say just how far before that time we can extrapolate it. Quantum gravity effects will come into play somewhere. Furthermore, we also know that inflation (or something equivalent) had to occur earlier, but we don't, as yet, know the precise time that inflation ended. And unfortunately inflation, like the standard big bang theory before it, doesn't include a sensible beginning.

So as of right now what happened prior to big bang nucleosynthesis is rather uncertain. We just don't have the experimental results to nail it down accurately. If we are able to nail down the precise properties of dark matter, we'll probably be able to extrapolate back in time a bit further. If we can detect primordial gravitational waves, we'll probably be able to understand the behavior still further back in time.

But as of right now, it's not actually clear whether or not we'll be able to build a theory about how our universe began that we can actually be sure is accurate. It's just a very, very difficult thing to measure, even in principle.

That's no nitpicking but a timely revelation. Thank you for the patience.

I'm glad :)

 

[Physics-Learner]

Regardless of whether one believes in the "big bang" or not, the above assumption makes no logical sense. The law of conservation of matter and energy to which you refer, is a physical law of THIS universe. We are not allowed to simply extrapolate and deduce that this same law would apply to a different or previous universe. On the contrary, since we know nothing of any universe but this one, we have to assume that the physical laws of THIS universe apply to THIS universe alone. As far as the "Big Bang" theory goes, all of the matter and energy that exists today was created by the event of the "Big Bang", so any discussion of physical laws of the universe must apply only to THIS universe and not to anything else.

exact a mundo, as the fonz would say.

this seems to fall on deaf ears. all that we know applies TO THIS UNIVERSE ONLY.

 

[yoda jedi]

If energy cannot be created or destroyed, that means all the energy that ever was and ever will be already exists. Wouldn't this mean that the universe has always existed? ..in one form or another. Everything that dies here on Earth goes back to the planet and new life is created. The universe could have this cycle as well.

I guess it's difficult for us to imagine something not having a beginning.

maybe there is a beginning but remotely so far ago, example in the andreas linde eternal inflation model.