Age of Universe: Big Bang, Braneworlds & Perspective

[KobiashiBooBoo]

TL;DR

Help grasp the concept that the universe has an age

Although I understand that time does not exist prior to the big bang, it's still a difficult concept that the universe - the sum of all that is and ever will be - has a beginnnig and therefore an "age." While we could say that time as a dimension began at the big bang, and it was meaningless before, is difficult for me to understand. Then there are the braneworld theories that indicate higher dimensional branes interacting which started our universe. I know we evolved on Earth so we are not selected to conceive of such things but I hope someone here can put things in persepctive for me and others.

 

[phinds]

First, the idea that the "big bang started everything" is a pop-science concept not embraced by actual scientists (even though you will hear some known physicists say that on pop-sci presentations).

The current theory of cosmological evolution is called the "Big Bang Theory" but it does NOT include a beginning. It starts about 13.7 billion years ago at the end of the theoretical (but highly likely) period of inflation, which itself does not start with a creation event. It is well understood how the universe evolved from that time.

If you rewind the cosmological clock back to zero you get to a point that pop-science presentation call THE BIG BANG and describe as an explosion in space that was the start of everything. What actual scientists say is that if you rewind the cosmological clock back to zero, you get to a point where our current theory has nothing to say and is not applicable.

 

[KobiashiBooBoo]

So the space between things was infinitesimally small (according to our familiar ways of measuring things - which is tied to our human experience) for perhaps an infinite period of time. Then inflation happened for whatever reason 13.7 billion years ago.

 

[Drakkith]

So the space between things was infinitesimally small (according to our familiar ways of measuring things - which is tied to our human experience) for perhaps an infinite period of time. Then inflation happened for whatever reason 13.7 billion years ago.

No, the universe was not infinitesimally small. If it is infinite in size today, it was infinite in size back then. The difference is that the density of matter was MUCH higher in the past. The big bang singularity is about the density of matter becoming so high that our math starts to give us infinities, which usually means we don't understand physics at that scale well enough to make useful predictions. In other words, our theory breaks down at that scale.

 

[KobiashiBooBoo]

If it is infinite in size today, it was infinite in size back then. The difference is that the density of matter was MUCH higher in the past.

This is a great way to understand it, I wonder why this concept is not communicated as much especially through the popular science channels.

 

[phinds]

This is a great way to understand it, I wonder why this concept is not communicated as much especially through the popular science channels.

Popular science TV channels are not about education, they are about selling soap / cars / etc. and pop sci books are about selling books.

 

[phinds]

So the space between things was infinitesimally small (according to our familiar ways of measuring things - which is tied to our human experience) for perhaps an infinite period of time. Then inflation happened for whatever reason 13.7 billion years ago.

I don't know where you got that from but it is pure speculation and likely not correct. The fact that the Big Bang Theory is silent on the question of any creation event does not mean there was no creation event, it just means we have no idea when/how it occurred.

 

[Drakkith]

I don't know where you got that from but it is pure speculation and likely not correct. The fact that the Big Bang Theory is silent on the question of any creation event does not mean there was no creation event, it just means we have no idea when/how it occurred.

To be fair, the universe isn't known to have a finite age, and the fact that our model predicts a singularity after a finite amount of time backwards is somewhat irrelevant since most of us agree that our predictive powers end at this point anyways. At best all we can say is that the universe as we know it is a bit over 13 billion years old.

 

[jbriggs444]

So the space between things was infinitesimally small (according to our familiar ways of measuring things - which is tied to our human experience) for perhaps an infinite period of time.

[emphasis mine]

There are various speculations for what happened earlier than what we have good evidence for. Some of those speculations have a history covering a finite range of times. Others have a history covering an infinite range of times (e.g. the "Big Bounce").

Either way, the intervals covered are "open". This is "open" in the mathematical sense like the open interval $(0, \infty)$ or the open interval $(-\infty, +\infty)$. Either way, there is no first instant of time. Nor any creation event. But one way the history of the universe is finite into the past and the other way the history of the universe is infinite into the past.

We like describing things with "manifolds". Manifolds are built with with "open" sets.

 

[vela]

This is a great way to understand it, I wonder why this concept is not communicated as much especially through the popular science channels.

It's quite possible that some of the popular science you've consumed said as much, but you just missed the point. There are a lot of intriguing ideas and concepts in cosmology, and it's easy to lose sight of what's understood vs. speculation. In addition, you need to recognize that our understanding of cosmology has evolved over time. It's not always obvious what the equations are telling us, and I think this has been particularly true in GR. Also popular science is necessarily imprecise by its nature—there's a reason why scientists use a lot of math. Finally, scientists are human, and some may not understand all aspects of the science correctly. They can often have the same misconceptions non-scientists have.

Despite all that, I don't subscribe to the cynical view @phinds has about popular science. Feynman, Weinberg, and others didn't write books simply to cash in. They found their work really interesting, and it's very human to want to share their work with everyone, not just other scientists. Communicating the ideas and concepts to a general audience is always going to require compromises, so it's almost never going to be 100% accurate. But hopefully it gets the general ideas across. As a consumer of popular science, you just have to be aware of these limitations.

 

[KobiashiBooBoo]

Thanks vela. I started my journey with Sagan as a youngster, and recently read Susskind, Smolin, and Greene - and the odd bits here and there. I have to say discovering this forum has been really informative. Better late than never!

 

[phinds]

Feynman, Weinberg, and others didn't write books simply to cash in. They found their work really interesting, and it's very human to want to share their work with everyone, not just other scientists.

I completely agree w/ that. I'm talking about Kaku and his ilk. There are very few people doing pop-sci presentation of the caliber of the two you mentioned. I see perfectly good scientists like Lawrence Krauss and Alex Filippenko sometimes saying things on pop-sci presentations that they would NEVER say in a room full of scientists.

 

[KobiashiBooBoo]

I completely agree w/ that. I'm talking about Kaku and his ilk. There are very few people doing pop-sci presentation of the caliber of the two you mentioned. I see perfectly good scientists like Lawrence Krauss and Alex Filippenko sometimes saying things on pop-sci presentations that they would NEVER say in a room full of scientists.

Can't stand Kaku or anything on tv. They aren't really going as in depth as they could. Greene takes liberties on his series but I enjoyed his first few books.

 

[PeterDonis]

Greene takes liberties on his series but I enjoyed his first few books.

You should be aware that his books take the same liberties as his TV shows. They might do it more subtly in some cases, but they still do it.

 

[berkeman]

Alex Filippenko

An EE friend of mine invited me to an auditorium presentation by Alex a number of years ago, where he discussed the amazing work of multiple teams that helped to understand and quantify the accelerating Universe. Brilliant ideas and technical work went into all of that work -- very impressive.

He was an engaging orator as well. It probably helped that most of the audience was technical in some way (the presentation was in Livermore California, not far from LLNL).

Filippenko is the only person who was a member of both the Supernova Cosmology Project and the High-z Supernova Search Team, which used observations of extragalactic Type Ia supernovae to discover the accelerating universe and its implied existence of dark energy. The discovery was voted the top science breakthrough of 1998 by Science magazine[2] and resulted in the 2011 Nobel prize for physics being awarded to the leaders of the two project teams.

Filippenko developed and runs the Katzman Automatic Imaging Telescope (KAIT), a fully robotic telescope which conducts the Lick Observatory Supernova Search (LOSS). During the years 1998–2008, it was by far the world's most successful search for relatively nearby supernovae, finding over 650 of them.[3]

His research, concentrating on optical spectroscopy, showed that many core-collapse supernovae result from massive stars with partially or highly stripped envelopes, helped establish the Type IIn subclass characterized by ejecta interacting with circumstellar gas, observationally identified the progenitors of some supernovae, revealed that many supernovae are quite aspherical, and showed that Type Ia supernovae exhibit considerable heterogeneity—crucial to the development of methods to calibrate them for accurate distance determinations.

https://en.wikipedia.org/wiki/Alex_Filippenko

 

[KobiashiBooBoo]

You should be aware that his books take the same liberties as his TV shows. They might do it more subtly in some cases, but they still do it.

Thanks, I'm not sure I have the background to identify those parts. For example, I did enjoy the string theory landscape explanations, but it took me a while to get the idea. I would not know if this was inaccurate, and I am sure things have changed since then. (re: Fabric of the Cosmos and The Elegant Universe)

 

[PeterDonis]

I'm not sure I have the background to identify those parts.

That's why we don't recommend trying to learn science from pop science sources--because they all take liberties, and unless you already know the science you won't know where the liberties are being taken. At least textbooks and peer-reviewed papers have some form of checking being done to try to ensure that liberties don't get taken. That doesn't always succeed, but your chances are still much better.

I did enjoy the string theory landscape explanations, but it took me a while to get the idea. I would not know if this was inaccurate

String theory has not made any testable predictions that are not made by other theories, so any claimed "explanation" of anything based on string theory is a speculative hypothesis at this point. Unfortunately, this is an area where even peer-reviewed papers don't always do a good job of preventing liberties from being taken.

 

[phinds]

That's why we don't recommend trying to learn science from pop science sources--because they all take liberties, and unless you already know the science you won't know where the liberties are being taken.

I watched a LOT of pop sci TV and read a LOT of pop sci books prior to finding PF. BOY HOWDY did I need to be disabused of a lot of what I "knew".

 

[vela]

I'm not sure I have the background to identify those parts.

The important thing is to be aware those parts are there so you can modify your understanding as you learn more. Also, recognize that you're at best getting an glossy overview of a topic from popular science. If you really want to learn physics, you need to take classes and use textbooks.

 

[KobiashiBooBoo]

The important thing is to be aware those parts are there so you can modify your understanding as you learn more. Also, recognize that you're at best getting an glossy overview of a topic from popular science. If you really want to learn physics, you need to take classes and use textbooks.

Many people aren't physicists or have the ability or time to become experts. That's why we need you!

 

[phinds]

An EE friend of mine invited me to an auditorium presentation by Alex a number of years ago, where he discussed the amazing work of multiple teams that helped to understand and quantify the accelerating Universe. Brilliant ideas and technical work went into all of that work -- very impressive.

I listened to the entire 96 1/2 hour lectures of his Teach-1-2-3 (The Great Courses) lecture series several years ago.

Filippenko is the author of and teacher in an eight-volume teaching series on DVD called Understanding the Universe.[7] Organized into three major sections in ten smaller units, this series of 96 half-hour lectures covers the material of an undergraduate survey course for An Introduction to Astronomy

Actual science throughout, no pop-sci crap at all.

 

[KobiashiBooBoo]

Here's the link: https://www.thegreatcourses.com/cou...erse-an-introduction-to-astronomy-2nd-edition

 

[KobiashiBooBoo]

Just re-read the above. I've learned so much since then. What an amazing thing to think about.