Looking at the Beginning of the Universe

Happy New Year!!

What was the size of the universe after inflation?

..." The standard model of cosmology would say that the universe is infinite which therefore does not have a "size". However, if we take into account that the big bang occurred

13.7±0.1713.7±0.17 billion years ago we can define a meaningful size for the observable universe. You might, for example, define the size of the observable universe as the distance a photon could have traveled since the big bang.

Consider, for example, a cosmic microwave background (CMB) photon that was emitted as visible light about 379,000 years after the big bang and is just now hitting our microwave detectors (the redshift is z=1089): that photon has been traveling for 13.7 billion years so it has traveled a distance of 13.7 billion light years. So you might imagine that the current radius of the observable universe is 13.7 billion light years. However, during this time the universe has been expanding, so the current position of the matter that emitted that photon will now be 46.5 billion light years away. (By now, the little 10−510−5 bumps on the CMB will have condensed into galaxies and stars at that distance.) This gives a diameter of the current observable universe of 93 billion light years. Note that as time passes, the size of the observable universe will increase. In fact it will increase by significantly more than two (to convert radius to diameter) light years per year because of the continued (accelerating) expansion of the universe. Also note that we will not be able to use photons (light) to explore the universe earlier than 379,000 years after the big bang since the universe was opaque to photons at that time. However, in the future we could conceivably use neutrinos or gravitational wave telescopes to explore the earlier universe.

So given a size of the current observable universe, we can ask how big was that volume at any particular time in the past. According to this paper at the end of inflation the universe's scale factor was about 10−3010−30 smaller than it is today, so that would give a diameter for the currently observable universe at the end of inflation of 0.88 millimeters which is approximately the size of a grain of sand (See calculation at WolframAlpha).

It is believed that inflation needed to expand the universe by at least a factor of 60 e-foldings (which is a factor of e60e60). So using WolframAlpha again we find that the diameter of the universe before inflation would have been 7.7×10−307.7×10−30 meters which is only about 480,000 Planck lengths."

Nod to FrankH

http://physics.stackexchange.com/questions/32917/size-of-universe-after-inflation

Wow, you certainly know this subject.

Thank you for trying to enlighten me.

Unfortunately, you repeated the same theories that I have problems with.

Sorry for my down to earth vision. I have difficulty accepting all these theories as facts when they "seem" to go against many laws of classical physic.

So, if I understand well, we only see the end of the inflation period, not when the universe was a small dot as everything was dark.

Thank you again.

Happy new year!

Here is how I've seen it explained: Light and other objects move through space but space itself expanded exponentially (inflation) at the beginning of the universe. (Points on an expanding balloon can become farther apart without anything having to move on the surface of the balloon.)

The speed of light is just the speed limit of anything moving through space. Space itself can expand much faster.

"Space itself can expand much faster."

I will need some time to accept this...

Thank you.

Space isn't traveling anywhere, so it isn't violating any laws of physics when it "expands".

The reason you are having a hard time wrapping your arms around it is because you learn physics from a Newtonian perspective all your life and when the curve ball of relativity comes by it doesn't make sense.

You have two choices here. Either you accept what is presented as truth by learned physicists or you engage yourself with the prospect of learning the mathematics that form the foundation of physics.

Unfortunately, you won't be able to simply stop at the foundation, you will need to go much deeper into your studies and research before it really starts to click.

Until then you really won't have much of an academic leg to stand on to challenge well established theories in the scientific community.

That's just the way it is. You are asking questions about a very deep subject and the only way you are going to make any real sense of it is to learn the language of mathematics at a level that goes beyond simple algebra and even calculus.

"The reason you are having a hard time wrapping your arms around it is because you learn[ed] physics from a Newtonian perspective all your life and when the curve ball of relativity comes by it doesn't make sense."

Precisely!

...and the math left me in the dust about 50 years ago. I was aware of relativity then, and have pretty much accepted it as fact, but still find it totally non-intuitive.

even conceited opinions are posted regardless of their provability

I would give you two good answers for this one if I could.

One for the puns and one for the good simplification.

I am starting to see the light (this punting is contagious )

Thank you!

Happy new year to you too.

the center of the universe is wherever I'm at

Once again you make things clearer. You are our hero...

Joke apart,

Thank you.

The creation of the universe was anything but sudden. The process still goes on to this day.

That doesn't mean that the universe didn't have it's busy days. :-)

Thank you for bringing our feet back on earth.

Happy new year!

Happy New Year to all!

I've been absent for a while, but and SE, AH and others have said more or less what need to be said about "The Beginning", except perhaps that there are present studies that try to construct viable theories of "before the beginning".

The universe might be cyclic, with contracting phases and 'bounces' resulting in expanding phases. The idea is not that the previous phases have contracted to 'zero size', but rather to Planck density, when the bounces might have occurred. Remember that the 'singularity' was never a size limit, but rather an energy density limit.

There is nothing in our current observations that rule out such scenarios, but there are ideas on how to look for tell-tale signatures in the CMB data. It may however take decades to find anything definite, for or against.

-J