# Thread: the outer limits of space-time

1. Greetings forum-members.

I have a quick question: in considering the "big bang", and what a thing to contemplate I can tell you, with the idea that it was a big explosion that expanded outwards from a small source, is it true that conventional theory accepts that there exists a type of big-bang wave front way out in the outer limits of the Universe, a wave front we can pick up with our best telescopes, way`est of way`out, as some type of minute/faint yet typically background radiation energy region that substantiates all conventional ideas of the origins of the Universe?

Thanks for any replies.

2.

3. No. It's kind of a weird thing to imagine, but the big bang didn't have an epicenter, or a central point where it expanded from. The matter and energy involved didn't explode, it was the space and time which exploded, and dragged the matter and energy along with it. In a very real sense, every point in the universe is the center of the big bang. From any point in the universe, if you look out in every direction, you'll see space expanding away from you like you're the center of an explosion.

The common analogy is a balloon. Draw two points on an empty balloon with a magic marker. They might have a distance of 2 cm from each other, roughly. Now blow up the balloon. Each dot hasn't moved on the balloon at all, as far as it is concerned, but the distance between the dots has increased. The dots represent matter and energy, and the balloon represents the fabric of spacetime. It's not a perfect analogy, so don't take it too far, but it's a good place to start.

At the start of the big bang, all points in the universe where infinitely close to all other points in the universe. This is easier to imagine if you think of the universe as having a positive curvature, since then it would be finite. But the math works for flat and negative curvatures as well. The big bang didn't expand into space, it expanded space.

This is all according to current accepted scientific understanding and big bang cosmology.

4. Thank you for your response.

If I may, though, "if the big bang exploded everywhere, as you said, and I know what you mean, what is the real map of the Universe....what exactly defines that "everywhere" doesn't include the outer universe that presumably has no stars.......why didn't the big bang happen there"?

(It's a very difficult subject, I do agree..........a lot of smoke and no mention of the mirror)

5. The big bang happened everywhere.

It's really easier to imagine if you assume the universe has positive curvature. Then it's finite, and if you travel far enough in one direction in a "straight line", you arrive back where you started. Much like the surface of a sphere.

So suppose our finite positively curved universe is .001 seconds old (or whatever), and has a volume of a few cubic meters. This isn't the volume of the "explosion", this is the volume of the empty space in the universe. It is impossible to travel in any direction and not be in this baby universe (you'll end up back where you started). Just like if you're on the surface of the Earth you can't leave the surface of the Earth just by walking (spaceships and digging not withstanding, obviously).

There isn't an "edge" to this baby universe, in the same way there isn't an "edge" on the surface of a sphere like the Earth. As it expands, all points in our baby universe become further away from all other points in the universe. Like on the surface of an expanding sphere (balloon). Imagine if the diameter of the Earth increased. There'd be more surface, but the oceans still have the same amount of water, so the ratio of land to ocean would increase. The oceans would become shallower and there'd be more dry land. Same thing with matter and energy. As the universe expanded, they became less dense ("shallower"), and there was more vacuum ("dry land"). But even with all this expanding there still isn't an "edge".

It so happens that this also works with other curvatures (flat and negative, where the universe is infinite), even though it's really hard to imagine

6. I understand your response and the picture, the virtual model in my minds eye, that you are painting.

But, it does seem that if the Big Bang happened everywhere, it wasn't the size of the basketball that some say was the size of the pre big-bang? That the big bang was the size of what we have, if it happened everywhere,.......and the idea of "expansion from a smaller reference" was a preliminary explanation to a theory of the Universe? What therefore of the theories that the Universe is expanding, or contracting? Understandably the red-shift makes us believe that the universe is expanding, but what of the journey of returning to the source when travelling far enough owing to the curvature of space?

7. Originally Posted by theQuestIsNotOver
I understand your response and the picture, the virtual model in my minds eye, that you are painting.

But, it does seem that if the Big Bang happened everywhere, it wasn't the size of the basketball that some say was the size of the pre big-bang? That the big bang was the size of what we have, if it happened everywhere,.......and the idea of "expansion from a smaller reference" was a preliminary explanation to a theory of the Universe? What therefore of the theories that the Universe is expanding, or contracting? Understandably the red-shift makes us believe that the universe is expanding, but what of the journey of returning to the source when travelling far enough owing to the curvature of space?
Over time, the universe (the time light takes to travel between points) has expanded. In a positively curved universe, its volume would be steadily increasing (it would take longer and longer for light to wrap around the universe and arrive back where it started). So even though it's difficult to imagine, the early big bang universe really could have been a single point. In the same way that an expanding Earth, if we went back far enough in time, might have had 0 diameter. Even if we don't think it makes sense, we should be able to imagine it.

That's the core of the big bang theory. The current universe seems to be expanding. Or rather, everywhere we look in the sky stars are moving away from us, with more distant stars moving more quickly. And since we assume the Earth isn't really the center of the universe, we assume that all points in the universe are moving away from all other points. That is, the distance between any two arbitrary points in the universe is increasing.

So if we extrapolate backwards in time, there was a time when the universe had 0 volume. When it was a single point. Light would have taken 0 time to arrive back at its starting location in a positively curved universe. If this really were the case, it would leave behind "scars" on our current universe that we would be able to observe. One such "scar" is the surface of last scattering (or cosmic microwave background radiation). There are some others, but that's the primary one most lay people know.

Keep in mind that actual observation indicates that the universe is either flat or really really close to flat. If the universe isn't positively curved, you can travel in one direction and never arrive back where you started. But a positively curved universe is easier to imagine and makes a lot of the explanation easier to see, and most of it holds no matter how curved the universe is.

8. So, essentially, you are suggesting it is possible to create a mathematic map of the universe as it exists today; you are suggesting there is a positive-expansion precedent in place, you know the equations of the speed of light, that space is curved, and that more distant stars are older (which takes me back to my initial point, namely, "what exists beyond that most furthest and dimmest and thus oldest star?"). Understandbly people get confused when taught the subject.

9. The universe probably is flat instead of positively curved, but yes, no matter what the curvature you can create a "topological" (mathematical) map of the universe. You wouldn't necessarily know where stars and galaxies are in the entire universe, but you could understand its nature.

Let's say the universe is 14 billion years old (roughly). That means the "observable" universe is a sphere with a radius of 14 billion light years. The edge of this "observable" universe is the surface of last scattering, and is what the universe looked like 14 billion years ago.

Let's magically travel to the edge of the visible universe. What do we see now? Galaxies and stars and dust and nova, exactly like on Earth, just not the exact same ones. This part of the universe is also 14 billion years old. If we look in the direction of Earth, we'll see what the Earth looked like 14 billion years ago (before Earth and the solar system existed, obviously). We'll see an edge of the visible universe, and the surface of last scattering where the Earth should be.

Now lets magically go out 28 billion years from Earth. What do we see? More of the same. Different galaxies, but still galaxies and stars and planets and all of that. All of it exactly 14 billion years old. And 14 billion light years from this new point we again see the surface of last scattering. If we look in the direction of Earth, we see a surface of last scattering where we just were, and where Earth sees one right now, but with the visible portion in the opposite direction of where Earth sees it.

If the universe is curved, eventually (300 billion light years? 100 trillion light years?) we'll end up back on Earth. If it's flat, we can go on forever and never see Earth. But we'll always find stars and galaxies and the like. And there'll always be an edge of the visible universe where we can see what the universe looked like at the moment of its creation, because that light is 14 billion years old and is just reaching us.

Anyway, this is what theory predicts. There isn't a way to actually magically travel 28 billion light years, so we can't back this up with direct observation. But there is a great deal of indirect evidence for this model of the universe. Enough for it to be the "standard" model of cosmology for scientists.

10. So, what's the point?

Why not leave the stars to astrolgers, as an entire scheme, a "please avoid this, it won't make sense, it's entirely impractical, and you won't make any money out of it in your life-time other than being a scientific hope-master for the possibility of future space-travel, which, if it does occur, would require the human mind to open big-bang doorways, to go into a wormhole of the big bang itself or hopefully uncover mormholes themselves intricately designed by fate to please our curiosity"?

In this age of recession, can we be sure that a study of the stars will provide answers for atomic phenomena here on Earth, especially if space and time is different in the outer reaches of space, that "space" we study of a distinctnly different time.

OR, can we JUMP to the conclusion that if the laws of space-time are uniform, let us make the big-bang some time of pre-required "axiom" of alertness, of vigilance, to "theory creation"?

11. A quick aside: one way to think of the surface of last scattering is as the horizon of the visible universe. There's stuff past that, we just can't see it.

As for the use of astronomy: it does make sense, if you're willing to stretch your mind a little. It definitely makes sense in a purely mathematical model, where you just manipulate equations and rules and don't worry about trying to imagine any of it. (This is called the "shutup and calculate" model of science )

As to whether it has any real world impact, I don't know. It's a lot like the national endowment for the arts. Any benefit it provides is not easily quantifiable. It is an entirely reasonable political position not to want tax payer money to pay for this sort of science. Just like it's an entirely reasonable position not to want tax payer money paying for the NEA or PBS, etc. It's not a position I personally hold, but I can respect it.

If you want to discuss the politics of it, open a new thread in the politics forum and we can discuss it there.

12. If we taske this issue to "politics", it might come back here on the debate of the real use of "physics" when looking at the stars.

I think my greatest doubt with contemporary physics is that they use "theory" to join dots without any mathematics to join those dots "directly". So, "theories joined together to produce other theories, more fundamental ones, while ignoring any pure independant mathematical link" is like passing the current "stimulus package bill" through the US senate: that there is no infrastructure, no real math in place to vlaidate their decison making.

I guess the real question is, "who is to say that the physics in the stars all that time ago is the same as our own "here and now""?

(late edit)

I have an idea: "can we suggest that the dimmest stars are the earliest ones, and thus the light that we see of them represents an embryonic stage of universal life, and that the less dim stars are more recently created and thus point to some growth of the laws themselves of space-time as we could perhaps know them"? Could the "red-shift" effect therefore be some type of "rusting" effect, or maybe "development" effect? Just an idea. Do scientists think of these things, things like this, this process of inquiry, such possibilities?

13. This is called the difference between positivism and scientific realism. In a positivistic philosophy, it is impossible to understand the underlying mechanisms of the universe. At best we can provide theories which explain as much of the data as possible. In scientific realism, the math of our equations are the actual equations the universe uses to run itself.

Something like string theory is more scientific realism. It's strongly based in pure mathematics, and attempts to understand the universe on first principles. In comparison, relativity was based more on positivism. There were some odd observations (speed of light is constant for all observers), and a theory was built around those observations to explain them. It suggested new falsifiable predictions, which were proven correct by observation and experiment.

I would argue that positivism makes for better science than scientific realism. The turn around time from odd observation to scientific theory to engineering is much shorter. String theory has been going at it for 30+ years and still isn't even properly done, let alone able to make many relevant falsifiable predictions. So IMO asking scientists to provide concrete theories grounded in a realist philosophy at best wastes resources, and at worst leads to decades of wasted effort. It's a good thing that the theories provided in cosmology are explanations based on data instead of derived from pure mathematics.

There are essentially five aspects of science:

1. Data Gatherer: without any input of ego, consistent measurements of natural phenomena are taken. There's no theory trying to be proven or disproven. It's just a humble record keeper taking notes on the way things actually are. In Astronomy, Tycho Brahe was such a man. These are the unsung heroes of science. This is not usually a profitable endeavor. It's also usually boring as hell.

2. Pattern Recognizer: based on the data gathered by the Data Gatherers, a law is formed to try and explain this data. There's no reasoning at this point, it's just identifying the mathematical relationship inherent in the data. In Astronomy, Kepler was such a person. He took Tycho's data, and formed Kepler's Law from it. This might be profitable since it allows prediction of future data.

3. Theorist: Based on the recognized mathematical relationship of the data discovered by the Pattern Recognizer, the theorist attempts to provide a theoretical bases for the data. Newton was such a person. In his Principia Mathematica, he presented his theory of universal gravitation. He also presented a new form of Mathematics to explain how his theory of universal gravitation can explain Kepler's Law. Calculus is probably one of the greatest inventions ever made by Man. It is absolutely invaluable to modern engineering. While there is a lot of prestige for a successful theorist, there's very little money.

4. Experimenter: Once a theory is created, it often makes falsifiable claims. In order for the theory to become widely accepted, Experimenters construct experiments to test it. Sometimes the theory is disproven and has to be entirely thrown out. This happened with the theory of the luminiferous aether, and led to the creation of relativity. There isn't usually any profit involved unless someone has a stake in disproving the theory (the link between tobacco and cancer, for instance, had many in the tobacco industry trying desperately to disprove it. There was a lot of money spent in this endeavor).

5. Engineer: was a theory is firmly established, engineers can use it to invent artifacts for mankind. Once relativity was established, it allowed for the Manhattan Project and the creation of a nuclear weapon. Engineering is highly profitable.

Now, all 5 aspects of science are extremely important. However, only #5 is really profitable. But you need the other four steps in order to get to #5. The time frame is usually decades between #1 and #5, and there are few businesses in existence today who can afford that kind of long term vision, so most privately funded science involves engineering and a little bit of experimentation (usually to disprove an "inconvenient" theory). Without public funding of science, only engineering would thrive. But with only engineering we wouldn't have electronics or space ships or ipods or anything like that.

Now astronomy has very little engineering aspect. We can't build a star, even if we knew how. However, some of the most important breakthroughs, which affect us in our everyday lives, occurred because of scientific work in astronomy. The invention of calculus allowed work in electronics many years later. Work that had little apparent value beyond astronomy at the time led to our modern affluence and way of life.

So I would argue for public funding of the first 4 aspects of science, even though there's little apparent benefit at the moment. It's the only way to stay competitive 50 or 100 years from now. Once the science gets to the engineering stage, it makes sense to turn it over to the private sector to make a profit on it, since they'll do so more efficiently than any government could. Except obviously weapon technology. You don't want the private sector building fusion bombs.

14. Originally Posted by theQuestIsNotOver
I have an idea: "can we suggest that the dimmest stars are the earliest ones, and thus the light that we see of them represents an embryonic stage of universal life, and that the less dim stars are more recently created and thus point to some growth of the laws themselves of space-time as we could perhaps know them"? Could the "red-shift" effect therefore be some type of "rusting" effect, or maybe "development" effect? Just an idea. Do scientists think of these things, things like this, this process of inquiry, such possibilities?
Dimmer stars do tend to be older, because they burn their fuel much, much slower than brighter stars. However, we know how far away they are. The light from a dim star 20 light years from us takes 20 years to get to us. The light from a bright star 10 billion years from us takes 10 billion years to reach us. That bright star from 10 billion years ago looks very similar to bright stars today. We thus have a lot of data about stars and their lives over the course of the life of the universe. And from this we can construct models of stellar evolution: how stars age as they get older. And these models seem to explain stars near us (and thus very recent in time) and far from us (and thus representing the universe billions of years ago).

What you call "rusting" sounds similar to the hypothesis of tired light. While you might be able to explain red shift using it, it doesn't explain the cosmic background radiation. There are other issues, too. As a result it is not commonly accepted by scientists.

15. Your "five step summary" is as you say it is, which is why when we entertain ourselves with ideas of living "lost in space" we may as well accept that we go back to "positivism" if all else fails.

My leaving remark in high school was, "success is the result of positive thinking": very mathematical, optimistic, and reflective at that. I was being reflective, at that: maths did me well.

I am just worried though that the hope to communicate with one another in (or about) a stellar environment has disallowed enough thought for ideas, possibilities, that we once thought (the ideas) clouded our judgment, clouded our vision, in not realising back then that we didn't have enough information available to bite that bullet on that pursuit......that it would come to nothing, a charity for those who merely could spin a good yarn.

It's like this, perhaps: "If there is a God, he would take care of all mystical things, all things entirely out of our reach, things like the stars.....for instance, in the hope we can design places here built on the hope of a peaceful night's sleep, when we really need the rest after a hard day in the field".

If we want to really invest in something, a flag, something that bears stellar entities, we should either be content in spinning a good yarn, or doing the math relevant to our basic and proper reference as decion-makers, and good ones, in this so-called universe.

(later edit)

So, who does the "buck stop with" in physics in a recession? Will our Governments more stringently aske "where the math is" after going through this new-millennium financial baptism of fire? Surely they will. It's a good thing. For the planet. For by which, in doing the math, you can open up a book of cause and effect on issues, incidents, variables, and outcomes, that point directly to a sustained and sustainable reassurance of certaintyfor as long as we can live in teaching our children the same language of survival, one that works.

16. It's not just clever stories. As I pointed out above, often these clever stories lead to very real engineering advances that improve all of our qualities of life. If we only funded based on mathematical truth, we would at best be wasting resources (Math is more labor intensive than theory), and at worst be sent on wild goose chases (just because something is mathematically true does not mean it represents the universe the way it actually is).

In the US, the National Science Foundation funds most of the #1-#4 steps of science. In a recession, it is often one of the first things to suffer budget cuts. Other times the government (especially under Democratic control) expands funding to promote educated job growth.

The NSF funds projects based on a funding review. To get money, you generally have to convince scientific reviewers that your research might be valuable. Scientific reviewers tend to be colleagues in your field, since they're the only ones smart enough to tell if you're just full of crap.

Which means that while the government as a whole decides how much money to give to science, it's the scientists in the field which police where that money goes. The existing balance between scientific realism and positivism in the American scientific community decides how the funds are allocated, so it's sort of a chicken and the egg situation. For funding to shift to more math based, the scientific community would first have to shift to being more math based.

17. I understand this process. Usually in times of uncertainty, internationally, to enforce newly-adopted trade tariffs the latest and greatest scientific wheels are flown in full-force. The works of cutting edge research "that works" to the point you may as well be using the planet as your own footstool. I am not foreign to that idea. It's the God of science, otherwise you may as well be Plato, hypothesising all day long as a poor freak.

With physics, though, ultimate advancement is geared along the nuclear-weapon front: technology that is not radioactive but very precise and effective..........just knocking out someone or something from a great distance. The ""how can we better harness the here and now atomic energy front" category. I don;t think that's going to go away.

18. I think that was true even as recently as 15 years ago, but modern military science seems more geared towards small scale logistics. Stealth, for instance. And defense against IEDs and RPGs.

19. I disagree............I hope. My hope is we are designing weapons to make us the marksmen, the sharpshooters, this planet may want us to be, to shoot down destructive influcences like wayward rocks from space, in our defense as a people, as a civilisation, to make this planet think that we actually can in all reasonable jutice represent it in moving on to greater spheres.......out there, somewhere......without feeling we have abandoned anything, but that the security continues.

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