Beginning of time

[Dominik Vugrinec]

Dear readers,

 

Welcome to this discussion it's a very weird topic and its been bothering me since the day i was managed to ask questions. Have you ever thought about the very beginning of time and the universe, I myself am not a very big believer in god and religion, it's not my thing. I am in love with Physics and to me it's a key in answering a lot of this big questions. The main question's that has been bothering me is what was before the big bang? How did energy just come to be (as stated in Conservation of Matter in chemistry is that matter can't be created or destroyed.) so how did this matter come to "life"? When exactly did time start, was it before the Big Bang or when Big Bang happened? 

This are just some of the questions that have been stuck up in my head and is it just me or does anyone think about this during the night when staring out into the stars trying to think what else is outside. 

 

Im really excited to see what you guys think of this and I hope I'm not the only one hahaha.  

 

Well, thank you in advance.

 

Kind Regards

 

Dom

[Emmi]

From one science aficionado to another, here's a short episode (it's about 40 minutes long) of a nonfiction science documentary series called How The Universe Works on cosmology and astronomy called "First Second." It goes through the first second of the Big Bang, and may start to answer your questions, or may give you more questions.

 

By the way, although we usually think of matter not being able to be created or destroyed, in some ways, it can. Matter and energy are linked by the equation e=mc², which means that matter is simply concentrated energy, and you can create matter out of energy and energy out of matter. Quantum physics actually allows for small random fluctuations to occur which allow particles to simply pop into and out of existence. A lot of cosmologists define time as starting at the instant of the Big Bang, and no one knows what happened before it (at least not yet!).

 

https://www.youtube.com/watch?v=zCTYJk_NpEc

[mechnight]

Thanks for the documentary Emmi!

 

I wouldn't really say there's been anything before the Big Bang. It was probably all some mess-up on quantum scale which started sort of a chain reaction, resulting in "Well.. Let it expand."

 

Btw Dominik, if you don't mind me asking, where are you from?

[Dominik Vugrinec]

Thanks for the documentary Emmi!

 

I wouldn't really say there's been anything before the Big Bang. It was probably all some mess-up on quantum scale which started sort of a chain reaction, resulting in "Well.. Let it expand."

 

Btw Dominik, if you don't mind me asking, where are you from?

Hi 

Im from Croatia, but i lived there only for five years, the first five years of my life. You could say I lived internationally my hole life. Im currently living in Abu Dhabi (U.A.E) where i will finish my IB Diploma. But this is a side topic. 

Thank you Emmi its a great documentary, to be honest i watched nearly every documentary on this kind of stuff and I must recommend my favourite "What the Bleep!? Down the Rabbit Hole" it's a great movie about Quantum Physics. And I'm really interested in that field and my personal goal is to finish a PHD in Physics. 

There i just gave you my short life story ahahaha.

Thank you guys in your replies.

Edited April 6, 2015 by Dominik Vugrinec

[Vioh]

Welcome to this discussion it's a very weird topic and its been bothering me since the day i was managed to ask questions. Have you ever thought about the very beginning of time and the universe, I myself am not a very big believer in god and religion, it's not my thing. I am in love with Physics and to me it's a key in answering a lot of this big questions. The main question's that has been bothering me is what was before the big bang? How did energy just come to be (as stated in Conservation of Matter in chemistry is that matter can't be created or destroyed.) so how did this matter come to "life"? When exactly did time start, was it before the Big Bang or when Big Bang happened? 

 

First, I’d like to thank you for such a good question. To be honest, I’ve done lots of research on this topic in the past but I didn’t truly understand anything, because it was so confusing. But thanks to you, I got my motivation back to actually study it seriously Now, it’s necessary to point out that this is a very hard topic & physicists are still struggling with it. The conventional Big Bang picture has been put into the so-called ‘hard’ science, but this picture doesn’t explain “what banged? why it banged? and what happened before it banged?” (Alan Guth). And with these questions being raised, there are still many debates in the scientific community about what theories are correct for describing the origin of universe. In the following 3 posts, I’ll try to point out some of the difficulties of this topic, as well as briefly rushing through one of the leading theories that we have nowadays (called the cosmic inflation). In the end, I will also mention Lawrence Krauss’ idea about the origin of universe, which is explained in details in his famous book Universe from Nothing.

 

Problem with asking what happened ‘before’ the Big Bang

 

As you probably know, Big Bang is the beginning of space & time. This means that it’s illogical to ask what happened ‘before’ the Bang, because the concept of ‘before’ relies entirely on the concept of time. But time didn’t exist until the Big Bang, so there’s no “before” of the Big Bang. It’s like asking what is the north of the north-pole? Well, the north-pole is the furthest north that you can go, so there’s no “north” of the north-pole.

 

The argument above is a very good one, in my opinion, but it doesn’t seem to satisfy anyone, because it is so mind-****ed. So Lawrence Krauss came up with a different argument. He thinks that this question of asking what happened ‘before’ the Big Bang is an interesting philosophical question, but an unimportant one. The reason is that even if there’s a model of what happened ‘before’ the Big Bang, there’s no way of testing it because we’re restricted within our own spacetime. Thus, this question doesn’t interest him as a scientist (because scientists want to test things empirically) (Source: 22:55). So what he proposes (which I’ll explain later) is that the universe can pop into existence by itself without any cause; and therefore, we needn’t bother ourselves with what happened ‘before’ the Big Bang.

 

Problem with Quantum Gravity

 

Quantum mechanics (QM) tells us that time can also be discrete just like how photons are the discrete particles of light. One discrete unit of time is measured in the Planck time (which is about ). There's no particular physical significance with this unit (i.e. it's not the smallest time interval), but it sets the upper limit for which the effects of quantum gravity are important (i.e. if you go to the time smaller than this interval, you will have to take quantum gravity into account). However, at this time scale, our physical laws (e.g. general relativity & QM) break down entirely, simply because we don’t yet have the theory of Quantum Gravity. This essentially means that it’s impossible for us to go back all the way to the absolute beginning of the universe (i.e. when time ). The conventional Big Bang theory that we learn in high school doesn’t start from ; it starts from when So things that happened from to is just an assumption in the conventional Big Bang picture.

 

Now, we tend to think that the Big Bang happened at . This is absolute correct, but it is not usually the way that physicists talk about the Big Bang. The reason is because the “Big Bang” has 2 different meanings:

• Meaning 1: Big Bang is the transition between the state of no space-time to the state of space-time. This is usually the way people would refer to the Big Bang, but it is a little problematic, because we have no idea what happened within the first Planck time during which Quantum Gravity took place.
• Meaning 2: Big Bang is the expansion of space-time from the very small to the very big, giving the universe as we see today. This meaning doesn’t address the problem of Quantum Gravity, but it talks only about the expansion of a very small universe to a very big one.

Cosmic inflation (proposed by Alan Guth) doesn’t explain the Big Bang as in the first meaning; rather it offers an explanation for the expansion of the universe from a very small size to a very big one (just like in the second meaning). Hence, it is completely valid to say that cosmic inflation successfully explains the Big Bang, even though it doesn’t take us back all the way to the absolute beginning of time.

Edited April 16, 2015 by Vioh

[Vioh]

Cosmic Inflation:

 

Here is a brief summary of cosmic inflation that ignores most of the mathematics that was used to predict this phenomenon. Inflation doesn’t start from the absolute beginning (as explained), but it originates from a very small patch of the universe (with the size of about in diameter). Inflation, which is based largely on general relativity (GR) & grand unified theory (GUT), suggests that this patch of universe is made up of a false-vacuum filled with false-vacuum energy. This false-vacuum energy is a form of positive gravitational energy and can produce a negative pressure, leading to the repulsive gravity that inflated our universe by a factor of about in only about seconds (i’ll explain the positive & negative signs later when I talk about the conservation of energy).

 

How did inflation end?

 

 

The graph above shows the energy of false & true vacuum states. Now, what inflation suggests is that during the period of inflation, false vacuum became so unstable that it then decayed to reach a lower energy state (the true vacuum state), by a process known as quantum tunneling (i.e. the state tunneled through the energy barrier between false & true vacuum states). And the energy released by this decay – which is basically the energy difference between false vacuum & true vacuum (see the graph) – was what that gave rise to matter & radiation that we see today (notice that this difference in energy has been staying constant with time, explaining why we have the first law of thermodynamics). The moment that the false vacuum decayed into matter & radiation was exactly when the inflationary period ended; and from there, the conventional Big Bang theory began. Notice that because false vacuum has positive energy and it later decayed into matter-radiation, this implies that the energy of matter & radiation is positive (remember this, because it’ll be important later on).

 

Now, what are the false vacuum & true vacuum really? Well, as you can see from the graph, both of them are just different states of the so-called scalar field (denoted by \phi). True vacuum has the lower energy level, which explains why the false vacuum decays into true vacuum, just like in the case of radioactivity that you learn in IB physics. But what is the scalar field really? This is hard to define, because the scalar field is actually the property of space itself. The stuff that causes this scalar field is somewhat ambiguous as far as my research can tell. According to Alan Guth (Source: 13:52), the false vacuum is just a state of matter at very high energies, and this is completely allowed within the GUT & GR. On the other hand, true vacuum is often associated with the so-called dark energy (which may be caused by virtual particles, popping in & out of existence as Emmi described). In general, the scalar field (either when it’s in false or true vacuum state) always has the effect of repulsive gravity which pushes things apart. But while false vacuum is responsible for the inflation of the universe, true vacuum is responsible for the accelerating expansion of the universe today. Another remarkable thing is that the energy density of the scalar field always stays constant even though the volume of space is increasing due to the expansion. The field just doesn’t dilute out. Here’s a quote from a Nasa's article:

 

“Empty space can possess its own energy. Because this energy is a property of space itself, it would not be diluted as space expands. As more space comes into existence, more of this energy-of-space would appear.”

 

This seems to violate energy conservation, but in fact, it doesn’t for the reason that I’ll explain later.

 

Summary of Cosmic Inflation

 

In short, inflation tells us that the universe started from a very small patch of space-time that was filled with positive gravitational energy of the false vacuum. This energy created a negative pressure, which then produced repulsive gravity that inflated our universe. Inflation ended when that positive false vacuum energy decayed into the positive energy that is stored within matter & radiation. And from that point on, the conventional Big Bang theory took over!

 

Inflation is currently the leading theory in cosmology because it can explain the Flatness Problem, the Horizon Problem, as well as the behaviours of the cosmic microwave background radiation (CMBR), all of which were not addressed by the conventional Big Bang picture. See more details here: 22:06

[Vioh]

Problems with Conservation of Energy in Cosmic Inflation

 

As I have mentioned, it seems that the picture of a cosmic inflation violates energy conservation. The problems are:

1. Where did the positive energy of the scalar field (which would later decay into matter-radiation) come from in the first place?
2. How can the energy density of the scalar field stay constant even when the universe is expanding?

The way of solving these 2 problems is to say that the positive energy of the scalar field is canceled out exactly by the negative energy of the gravitational field that is being created at the same time (notice that the gravitational field can store negative energy because it’s attractive). Remember that I said that the scalar field can create negative pressure? Well, the reason lies in the relationship between the pressure () & the energy density of the scalar field () which is described by . Since the data tells us that is positive, then the pressure must be negative! So the pressure being negative is basically the result of the mathematics.

 

Now let’s use an analogy to visualize negative pressure. Consider a balloon that is filled with gas, then what happens when the balloon expands? Well, according to the laws of thermodynamics (as studied in IB physics), the gas inside would exert a positive pressure on the balloon – which means that the gas does work on the balloon, causing the gas to lose its total energy. But if the gas exerts a negative pressure instead, then the whole thing is reversed, which means that when the balloon is expanding, it does work on the gas, causing the gas to gain its total energy. Similarly, because the scalar field exerts a negative pressure, it gains energy as the universe expands!!! Now, the analogy doesn’t work very well here because it’s hard to find the analogue for the balloon itself. But the important point here is that even though the scalar field gains energy due to the expansion, this newly-added positive energy of the scalar field also causes more curvature in space-time due to GR, thus adding more negative energy into the gravitational field. This negative energy will cancel out the positive energy, thus there’s no violation whatsoever! In fact, this is the reason behind the idea of a zero-energy universe. See more in details here (30:14) & here (51:00)

 

Lawrence Krauss’ Universe from Nothing:

 

Much of the content of Krauss’ famous book Universe from Nothing is actually about the cosmic inflation model of the universe; so his idea resonates very well with what I’ve written above. However, Krauss also adds some extra bit to explain the Big Bang as in the first meaning (i.e. he wants to extend the laws of physics back to the absolute beginning of time when ). Notice that even though Krauss understands that the problem of Quantum Gravity has not yet been solved, but he thinks that it’s fine to do some speculations about what really happened at , using the laws of physics as we know them. His idea is as follow:

 

The law of quantum mechanics (QM) tells us that space & time can actually be quantized (i.e. be divided into discrete unit). QM also tells us that quantum objects can undergo quantum fluctuation, which is caused by Heisenberg’s uncertainty principle (HUP). This is precisely the reason why virtual particles can spontaneously pop into existence from nothing (see the Casimir Effect). However, the problem with virtual particles is that they need positive energy to pop into existence, which they can’t get from ‘nothing’. So they have to disappear very quickly afterwards, such that they don’t violate the conservation of energy as indicated by HUP. That’s why they are called ‘virtual’, as they disappear too quickly for us to ever observe them directly.

 

Now, the idea that Krauss proposed is that at , spacetime could pop into existence by the process of quantum fluctuation. However, our universe didn’t disappear right away as in the case of virtual particles, because the total energy of our universe is PRECISELY ZERO, and it would always stay zero because the positive energy of the false vacuum is canceled out by the negative energy stored in the gravitational field. For this reason, the existence of our universe doesn’t violate the law of energy conservation, even if it stays in existence for a very long time. See more details here (51:07)

 

Krauss’ idea is possible & plausible. However, he seems to get lots of criticism. For example, Frank Wilczek (a Nobel laureate) thinks that it’s too early for us to speculate about what happens at time ; he thinks that we are far from understanding what happened at the very beginning of time, especially when Quantum Gravity has not yet been understood (see 19:50). Wilczek’s criticism is a fair point, in my opinion. However, I’m still glad that Krauss proposed this idea of universe from nothing, because it shows us that it’s not entirely impossible for science to address these hard questions without resorting to some sort of God.

 

Recommended lectures & videos:

• Alan Guth's non-technical lecture about inflation

• Alan Guth's technical lecture about inflation

• Lawrence Krauss debating with philosophers in Stockholm

• Lawrence Krauss talking about Universe from Nothing at the Nobel Conference & his discussion with other physicists

• Sixty Symbols' short video about inflation

PS. I’m not too sure of all the facts I have written. Hopefully they are all correct. Maybe you can do some research for yourself, and see whether you will reach the same conclusion as I do