What Happened Before the Big Bang?

The Bad Astronomer writes to tell us that a recent advance in Loop Quantum Gravity theory appears to allow the mathematics of cosmology to be extended to the time before the Universe underwent the Big Bang. Bad Astronomer also attempts to simplify things a bit with his own explanation of the new discovery.

The Paper & Article

[eldavojohn]

What Bojowald's work does, as I understand it (the paper as I write this is not out yet, so I am going by my limited knowledge of LQG and other theories like it) is simplify the math enough to be able to trace some properties of the Universe backwards, right down to T=0, which he calls the Big Bounce.

I caught this story on PhysOrg [physorg.com] yesterday and subsequently found the full text [nature.com] from the Journal of Nature Physics. While Mr. Bojowald has many papers currently up for review, I believe the precise paper is available on Arxiv [arxiv.org].

As Bad Astronomer noted, this isn't the first time something like this has been proposed. I think the first time I read about it was in a book by George Gamov [wikipedia.org] and then subsequent work/proposed theories done by Roger Penrose [wikipedia.org] & the well known Stephen Hawking.

Considering past results of my comments [slashdot.org] on matters I have little formal education on, I'll won't bother to remark on this work.

Re:There is no before the Big Bang.

[khallow]

While we don't have a working theory of quantum gravitation, we do have some strong hints that time and and space themselves were forged in the Big Bang. If you look at a Universe a Planck Length is size, the error in the time of any event observed would be longer than the time the Universe has existed for, to this point, and any error is position would be large than the current Universe at that size.

Time and length can be measured simultaneously without problem. Position, momentum and time, energy are the pairs that are subject to the Heisenberg uncertainty principle and cannot be measured simultaneously to arbitrary accuracy.

In short, time and space are useless measurements of a Universe this small.

But with high energy and momentum density, I think time and space make sense. And that's assuming that the Big Bang is a singularity with initial time origin.

Re:There was the sound of God asking for my zippo

[Anonymous Coward]

So basically, the universe is just one giant flaming God fart?

According to Peter Griffin [youtube.com], yes.

Re: Enter the Sphere

[Ucklak]

There are 3 'north' poles.

Only in the context of magnetic navigation does your comment relate to the magnetic north pole.
The magnetic pole is not fixed and is based upon the iron core of our planet. It has a deviation [noaa.gov] and changes over time and location.

There is the political north pole which cartography is based upon. This is where we get nautical measurements from. It is 5400 nautical miles from the North Pole to the equator.
90 degree right angle from pole to equator; 60 minutes each degree, 1 nautical mile per degree : 90*60 = 5400 nautical miles.

Then there is the axial or celestial 'North' pole which is where our 23 degree tilt comes from. That measurement is not a constant either as our planet has a `wobble`.

Re:Big Crunch vs Cold Death

[Ambitwistor]

Bojowald's original "bounce" solution merely has a single crunch which leads to a single bang. It also ignored the cosmological constant, which is what leads to the eternally accelerating expansion (dark energy) now favored. This does not by itself mean that loop quantum cosmology is incompatible with observation. It is possible (although maybe odd) that the universe could expand forever after the Big Crunch of a single progenitor universe. However, more importantly, the simple and highly symmetric LQG solutions so far considered are much more idealized than the actual universe, so it's quite probable that no truly realistic LQG solution has yet been written down. It's just a first step, to be able to write down any quantum gravity solution capable of describing the Big Bang.

A graint of salt

[Ambitwistor]

This result is interesting within the context of loop quantum gravity, because it offers an approximation within which the Big Bang can be modeled directly. However, it's worth not losing sight of the fact that the LQG theory upon which it is based has serious issues with consistency. It is based on a non-standard quantization technique with no experimentally supported basis, its Hamiltonian constraint has never been solved (which renders any approximation based on that constraint suspect), and it suffers from potentially infinitely many quantization ambiguities (again, with no known and maybe no possible experimental method for singling out the correct quantization. Some of these concerns are summarized here [arxiv.org]. (Yes, it's written by string theorists, and yes, string theory has its own set of problems with experimentally selecting the "correct" solution. But the correctness of string theory aside, the objections raised in that article against LQG are valid.) It's very premature to suggest that LQG's picture of the Big Bang may be correct when the fundamental theory itself has serious unresolved problems.

Re:There is no before the Big Bang.

[TrekkieGod]

It's not measurement that's the problem. It's existance. A quantum object does not have a well-defined position/momentum.

More information, please? This assertion is the fundamental problem I've always had with quantum theory, and every time I ask someone who thinks they know what they're taking about to explain it, they wave their hands around a bit, say "Heisenberg" a few times, then claim it's lunchtime and they really must go. The uncertainty principle as I've always had it explained to me (for instance, in my university physics course) is that observation of (ie. interaction with) a particle affects that particle in a way that you can't determine, and hence it isn't possible to simultaneously measure some quantities. There seems to be a big jump from "can't measure" to "doesn't exist" and no-one seems willing to talk about it.

I'm not a physicist, I'm an EE. I took one semiconductors class in college that touched a bit on this, and we didn't go very deep, so take this with a grain of salt. If I'm wrong, I'd appreciate very much if someone who knows more than I do can correct me. No experiment can ever, no matter how perfect, no matter how much technology improves, measure position and momentum so that the uncertainty on the measurement of momentum times the uncertainty on the measurement of position is less than the planck constant divided by 4 pi. This isn't due to the effect the observation has on the particle. Even if the observation has absolutely no effect on the particle, that's the best you can do. For example, if you two particles are entangled, and you make your measurement on one of them, your observation did not physically interact with the second particle. Nevertheless you still won't be able to measure the position of one of the entangled particles and then measure the momentum of the other and end up with values to a more precise degree than the one described in the equation above.

There are multiple interpretations for what is actually happening that prevents us from getting more precise measurements. Some of these interpretations assume that the reason we can't measure them is because the quantum particle honestly does not have its position and momentum well defined below that point. That seems to be the more accepted interpretation these days, although that wasn't always the case, which is why you were taught that the observer effect is responsible for the measurement uncertainty. Whatever is really going on however, we are sure that the uncertainty in measuring position and momentum is completely independent from the observer effect. Even if your experiment does not disrupt the particle, and even if your measurement device for position and your measurement device for momentum each are somehow individually more precise to values far below planck constant / 4 pi, you still won't be able to make a measurement on a particle without affecting the other measurement.

Einstein and Bohr had some some serious disagreements over the issue. Einstein believed as you do that you should be able to make those measurements given a proper experiment. Bohr held the opposite view. The Boh-Einstein Debates [wikipedia.org] are extremely interesting reading on the subject, and I recommend you take a look. These were two brilliant scientists trying to stump one another, so the arguments on each side were great.

Re:There is no before the Big Bang.

[xPsi]

You are basically right on (IAAP). Here's my two cents into the thread:

There are are lots of different ways to understand the Heisenberg Uncertainty Principle physically -- most of them not very satisfying without acclimating to the lingo and concepts of quantum theory. Nevertheless, I think one can gain an intellectual foothold into the idea, before even digging into the quantum theory, by realizing that ALL wave behavior (sound, water, radio, light, etc.) obeys something akin to a HUP. If you can get the basic idea down for sound or water waves, then you can start to build a conceptual bridge to matter waves. Since you are an EE, the conceptual underpinnings will probably look quite familiar.

Lots of mathematical qualifications aside, basically ALL waveforms can be represented by a sum of harmonic waves (pure sine and cosine functions). A single pure sine or cosine has a well defined frequency, wavelength, and wave velocity. However, in contrast, an arbitrary waveform does NOT have a single wavelength or frequency -- it has many, given by the distribution of sines and cosines that were used to construct it. A handy variable to use is called the wavenumber, which is basically the number of cycles per meter (proportional to 1/wavelength) of a harmonic wave. An interesting thing to do is plot a particular waveform, say a snapshot of a water wave shaped like a lump at a moment in time, and then also plot the distribution of wavenumbers from all the sines and cosines making up that lump. They are two representations of the same object. One looks like a water lump in space, and the other will look like another lump telling you the distribution of sines and cosines in "wavenumber space." What you find is that if your water lump in space is narrow, then it takes many sines and cosines of many wavenumbers to make that happen. If the water lump is very spread out, you only need a narrow range of wavenumbers of harmonic waves to make this happen. Many engineers are very familiar with this bandwidth effect in the context of transmission theory, but the same will be true for ANY waveform. It is a byproduct of wave theory: the width of the spatial distribution of an arbitrary wave is inversely related to the width of its wavenumber distribution. If you allow the wave to change in time, you get a similar inverse relation for the distribution of the wave in time and the distribution of frequencies in the wave. You are probably familiar with all that in the context of Fourier analysis etc. One says that wavenumber and position are "complimentary" (so are frequency and time).

The big leap in quantum mechanics is that the momentum of a particle is inversely related to the wavelength of some harmonic wave "associated with" the particle. The larger the momentum, the shorter the wavelength of the matter wave and vice versa. That is, momentum and position are complimentary variables. Keep in mind, the wave isn't the particle itself but rather tells you where the particle is likely to be. Once you accept the rather odd idea that momentum and wavelength are inversely related, *wave theory alone* tells you that the more likely a particle is to be at a particular location in space, the wider its distribution of wavenumbers is -- and thus the wider range of momenta it can have. Similarly, if you have a very narrow range of wavenumbers, the wider the spatial extent of the matter wave -- thus for a well defined momentum the particle has a wider range of spatial positions available to it. This is basically the heart of the Heisenberg Uncertainty Principle.

Since this matter wave tells you about probabilities, you need to prepare an ensemble of identical objects and do a statistical analysis of their positions and momenta to see the effect of the HUP. For example, lets say you prepare 100 particles each with a well defined position. Now you perform a position measurement followed by a momentum measurement for each particle. Taking your raw data, you made a plot of the number