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Q & A: Why does the universe exist?

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Most recent answer: 11/12/2016
Why does the universe exist?
- Navneeta
Timpany School, Vizag,Andhra Pradesh,India
Navneeta -

Whoa! Thatís quite a question! And the answer actually lies on the border between science, philosophy, and stuff we just donít know. But rather than answering it myself, let me give you a (rather long) quote from Dr. Leon Lederman, a very cool (and quite famous) particle physicist:

"In the Very Beginning there was a void -- a curious form of vacuum -- a nothingness containing no space, no time, no matter, no light, no sound. Yet the laws of nature were in place, and this curious vacuum held potential. Like a giant boulder perched at the edge of a towering cliff . . .

Wait a minute.

Before the boulder falls, I should explain that I really donít know what Iím talking about. A story logically begins at the beginning. But this story is about the universe, and unfortunately there are no data for the Very Beginning. None, zero. We donít know anything about the universe until it reaches the mature age of a billionth of a trillionth of a second -- that is, some very short time after creation in the Big Bang. When you read or hear anything about the birth of the universe, someone is making it up. We are in the realm of philosophy. Only God knows what happened at the Very Beginning (and so far She hasnít let on).

Now, where were we? Oh yes . . .

Like a giant boulder perched at the edge of a towering cliff, the voidís balance was so exquisite that only whim was needed to produce a change, a change that created the universe. And it happened. The nothingness exploded. In this initial incandescence, space and time were created.

Out of this energy, matter emerged -- a dense plasma of particles that dissolved into radiation and back to matter. (Now weíre working with at least a few facts and some speculative theory in hand.) Particles collided and gave birth to new particles. Space and time boiled and foamed as black holes formed and dissolved. What a scene!"

(from , copyright 1993 by Dr. Leon Lederman and Dick Teresi, published by the Houghton Mifflin Company.)

He goes on to describe the universeís growth and expansion, but the important part for your question is right here. Basically what heís saying is that the universe exists because it can exist. Before the universe, there was nothing. But there was the chance for that nothing to become the universe. And since the possibility existed, it was bound to happen eventually. And so here we are.


[There are other possible pictures suggested since that was written, as mentioned below.]

(published on 10/22/2007)

Follow-Up #1: quantum creation

So that means the universe exists because there was a chance to be born, and I think that is very close to the quantum mechanics way to think. And the basics of the quantum theory is that every possible outcome from every moment should be performed. So there are some conclusion from that way of think-the basic is that there is no God or something like this, and everything is like this because all probabilities must be covered. So what do you think of that :)
- Mitko,age16
Although the answer didn't use the word 'quantum', you were very perceptive in noticing that the explanation was entirely based on quantum mechanics. Lederman's version did not explicitly assert that all quantum outcomes occur (the many worlds interpretation) but that would indeed help explain details of our universe.

You're right also that we try to go as far as we can with explanations based on observations and the mathematical theories they inspire, without invoking other hypotheses.

Mike W.

(published on 10/22/2007)

Follow-Up #2: origin of universe?

1. If universe came out from absolute void, how the possibility or potential for the universe to fall in reality was contained. Also how the click, required for execution/ start of big bang, created itself. 2. In case of big bang, how singularity (which is too simple and plane), gave the birth of complex universe means how all the information of even my single finger or an ant in Africa, existing at certain point of time-space, was preserved in so called potential of asolute void. 3. There exists no reference out of the universe so the existence of universe is self referential and as the self reference leads to nothing, how universe is believed existing. Please don't tell me it is so vivid. 4. I will put next questions after receipt of answers from you. 5. See you.
- Muhammad Shehryar Khan (age 45 years)
DG Khan, Punjab, Pakistan
1. At this point, I think that the 'absolute void' picture is not very much accepted. In some sort of consistent quantum gravity picture, the singularity of General Relativity will be removed. That probably means that the beginning of our spacetime will somehow connect up with a broader manifold. Needless to say, there are some serious speculations underway concerning how that works. There are even some distinct predictions of different pictures for the ripples in the cosmic microwave background. Notice that there has actually been some progress since Tamara wrote the first answer in this thread.

2. That's a challenging question. If the time evolution of the quantum universe has the properties of quantum field theory (unitarity) then information is somehow conserved. There are disputes about how to integrate that feature with gravitational horizons. If I understand correctly, the current consensus is that unitarity does hold, and that quantum gravity should remove the problems not only at the origin but also at black hole horizons.

3. This is a deep philosophical question. That's another way of saying it's too hard for us.

Mike W.

(published on 05/16/2011)

Follow-Up #3: Why do laws of nature exist?

Dr. Lederman didn't really answer the question. He just pushed it back a level. From the original answer: "Yet the laws of nature were in place, and this curious vacuum held potential." To rephrase the original question: Why do laws of nature exist?
- Walter (age 37)
Hudson, NC USA

We have no idea. It's hard to even imagine what an answer would be like. Yet it's tempting to wonder about.

Mike W.

(published on 02/26/2014)

Follow-Up #4: Will the universe stop expanding and start contracting?

As we know that the universe was started after the big bang, the energy released from the big bang has created the matter and from that matter galaxies and planets were formed. As we know that the universe is expanding due the dark energy,. But a time would come when this dark energy will get depleted and gravitational force will become more stronger than dark energy. And thus contraction of the universe will happen and again the big bang would take place, this process will continue and the big bang will take place again and again thus in the reality we should consider both big bang theory and steady state theory also as per the law of conversation of energy the energy remains same every time. Thus everything gets repeated in the big bang, like to say, if I am writing this and you are reading this, This things have being happen before at the time of big bang that took place before, and this will happen at the time of big bang which will take place again. Can this be true?-DIVYA
- Divya barmeda (age 14)

There are several plausible theories of the fate of the universe, the one you are proposing is one of them.   However there is experimental evidence that the universe is actually expanding at an ever increasing rate.  This is attributed  to "Dark Energy", which contributes a repulsive term in the Friedman equation that describes how the energy in the universe drives its expansion.

You might want to check out some of these references:


Just to add a few responses to some points in your question: 
1) The dark energy doesn't cause the expansion, it just gradully speeds it up.
2) So far as we can tell from various lines of data, the dark energy density isn't changing. It's not being "depleted". Ordinary matter density does go down as the universe expands, so that makes the acceleration increase a little. As Lee's links point out, however, we don't know what will happen in the very long run. /Mike W.

(published on 11/12/2016)

Follow-up on this answer.