Sunday, April 22, 2007

Einstein - Relativity

In reading a review of two new books on Einstein this morning, I had this odd thought. Under the theory of relativity we are able to study the light coming to our planet which bears images of billions of years past. Currently some scientists claim that we are able to see to approximately 500,000 years after the big bang. So with that set up, here is the question: If the entire universe was compacted into this little ball of matter and energy prior to the big bang, at some point there will be no light for the telescopes to see. If there was something prior to the big bang, and it gave off light, will we be able to see past the point of no light to the place where there was light?

9 comments:

bernardo said...

This is an aspect of astrophysics I do not claim to really understand myself, but apparently there was no space or time before the big bang. I don't know why this is necessary in order for big bang theory to make sense, but it's what I keep hearing from physicists. So there could not be anything "before" the big bang. And during the big bang, there could not be anything other than the big bang. Again, I know I am not explaining this idea very well, and I don't know why so many scientists think it's true. I'm just saying that the answer to your question probably lies somewhere in this direction.

In essence, though, you are right in that, since the universe is growing at a constant (or smoothyly-changing) rate, there is some distance such that no light should come from beyong it. If light does come from beyond it, this probably means that the big bang theory would need re-workng. But, again, I am not a physicist. I do pride myself in knowing some of the fundamentals of quantum physics and astrophysics, but not so much the big bang stuff.

(Especially don't ask me about how the elemental particles during the big bang coalesced into the particles we have today. That's a huge field of study, and pretty much all I know about it is that it exists and that it generates confusing graphs once in a while).

Tom Foss said...

So with that set up, here is the question: If the entire universe was compacted into this little ball of matter and energy prior to the big bang, at some point there will be no light for the telescopes to see.

What? How in the world do you come to this conclusion?

Most of the light we see was and is generated by stars. Light moves at a constant speed (in a vacuum) of 3.0x10^8 m/s. So in one second, a photon (a particle of light) travels 300,000,000 meters (give or take--that figure's rounded off a bit).

The direct information that we have about the early universe is mostly the Cosmic Background Radiation. When the Big Bang theory was first developed, one of the predictions was that, since the universe was once a hot morass of high-energy photons and plasma, there would be some remnants of that energy, cooled substantially in the billions of intervening years. Not too much later, some scientists inadvertently discovered that background radiation, and the measurements fit the predicted values so well that the error bars don't fit on the graph.

Anyway, I imagine that when you say that scientists can see back to 500,000 years after the Big Bang, that's what you're talking about, the Cosmic Background Radiation (CBR)that lingers like a low-energy afterimage of the early universe.

Now, I think what you're getting to here is that eventually we'll be able to look so far back into the past that there's nothing to see. What this demonstrates to me is a profound misunderstanding not only of what the Big Bang theory suggests, but of how we obtain information about the early universe.

The CBR shows to us a time when the average temperature of the universe was 3,000K, or about 2/3 the temperature of the surface of the sun. It's around this time that the universe had cooled enough (through the expansion of space) for hydrogen atoms to form. Before this, there were no stars (and for quite some time after this as well), quite simply because it was too hot for stars to exist. So the only thing producing light was the entire universe.

It's possible that we'll be able to look past that someday, but I'm not sure how. The cosmic background radiation is quite literally the remnants of that early hot universe, where high-energy photons and electrons filled space. As space has expanded, those electrons and photons have cooled, some have gone into the formation of the various celestial bodies, and what radiation remains is spread out and cooled to a very, very low frequency. By measuring the fluctuations in this frequency, we can get an image of how the universe looked billions of years ago, but it's a snapshot, not a time machine.

For all of the objects in the universe, we can only see them once light generated from them or bounced off of them reaches our surface. We don't see the sun as it is, but as it was eight minutes ago. If something is 1 light-year away, it means it takes one year for light to reach us from it, and we are seeing it as it was a year ago. Some stars are thousands and millions of light-years away, which means that the light reaching us from them was first emitted eons ago. We can only see out into the universe the light that has had enough time to reach us, and that's a limiting factor.

And that's why it's so neat that we have this CBR; we can see it because it's already here, it's all around us, because at one time in the distant past, it filled all of space.

If there was something prior to the big bang, and it gave off light, will we be able to see past the point of no light to the place where there was light?

Again, you have a very profound misunderstanding of what the Big Bang theory states. First, the Big Bang was an explosion not just of matter and energy (like the explosions you may see in an episode of the A-Team), but of spacetime itself. At one point, the zero point of the universe, all the matter and space was compacted into an infinitely small, infinitely dense ball. The subsequent expansion was of space, not just energy.

Here's a hypothetical to illustrate this: let's say you and I are standing in the early universe. We're standing 1 meter apart, and the universe is expanding at a rate of 1 meter per second. After 1 second, we would be 2 meters apart. After 30 seconds, we would be 31 meters apart, and so on. The actual space we are standing in is expanding, and we are being pulled along with it.

Now, that was very, very simplified, and ignored the actual properties of the early universe, as well as the expansive effects that might occur on matter or whatever as well.

What Einstein contributed to the equation was that time is another dimension (along with the three spatial dimensions: length, width, and depth), and taken together we call these dimensions "spacetime." The Big Bang was an expansion of spacetime, as well as energy. So, it makes no sense to say something like "before the Big Bang," since the Big Bang was essentially the beginning of the passage of time.

One of the other consequences of the theory of relativity is the existence of singularities. General relativity suggests that gravity is an effect of matter on spacetime, where the very fabric of space warps around a mass. The common model is that you imagine a big black rubber sheet. This is space. Now, if you toss a bowling ball onto that sheet, it will make an impression, warping the sheet around it. If you drop some smaller objects onto the sheet, they will be pulled into that depression. That's basically the relativistic view of gravity.

Well, there are some objects that are so massive and so dense that they warp space around them so tightly that not even light can escape them. In common parlance, we call these things "black holes," but in technical terms, they are singularities. Now, inside of a singularity, things are so twisted that there is nothing we would recognize as the passage of time. If you were to fall into a black hole, you would be falling forever, and you would be falling faster at one end than at the other.

Well, the zero point of the universe, that moment before expansion, is also a singularity. The best mathematical models can only wind the clock back to a fraction of a second after the expansion started, because before that you have this infinitely dense ball of energy and space for which there is no passage of time.

So, while there's the potential to see farther back than 400,000 years after the Big Bang, the conditions of the early universe and the physics of why we can see even that far back would suggest that it's unlikely. We may never see back to the event itself, and talking about things "prior to the Big Bang" are essentially nonsensical, because the Big Bang was an absolute zero for time in this universe.

Incidentally, nothing about the theory of relativity, in either the special or general case, allows us to "study the light coming to our planet which bears images of billions of years past." Relativity tells us some interesting things about that light, but has little to do with allowing us to study it.

Randy Kirk said...

WOW! Thanks Tom, I think. Now I feel like I need to go read a book on this.

Let me see if I understand a couple of things. If light is made by or reflected by some object in space, when we see the light we are seeing history. To the extent that we are able to view the item in detail, wouldn't we be seeing weather or other activity that happened then, as opposed to right now?

If that's the case, the oldest light source we can see would do the same, correct?

Then, you say, prior to that, there was a time when there was no visible light, and we have detected this. With what?

And then, in the beginning, there was this infinitely dense ball of energy, matter, and space. Didn't earlier theories suggest that prior to the big bang, a prior universe may have imploded into this ball? What have we learned to make this impossible? If it isn't impossible, would we be able to see light from that universe?

What percentage likelihood would you personally give to the Big Bang theory? Knowing that we have almost no knowledge of how clouds work around our own little planet, can you imagine giving it a likelihood above .1 percent.

Tom Foss said...

Now I feel like I need to go read a book on this.

Better yet, call up your local community college or something and see if you can get an appointment with an astronomy professor.

Let me see if I understand a couple of things. If light is made by or reflected by some object in space, when we see the light we are seeing history. To the extent that we are able to view the item in detail, wouldn't we be seeing weather or other activity that happened then, as opposed to right now?

To some degree, yes. The problem is that the only things we can view in any detail right now are stars. We don't have telescopes powerful enough or with enough resolution to see any but the largest, hottest, most gaseous planets ("hot Jupiters" as they are sometimes called). If we could see a planet in detail, then we would effectively be looking into its past, as many years ago as it took the light to travel here.

Just as when we look at the sun, we are seeing it's past, about 8 1/2 minutes ago, the time it takes light to travel the 93 million miles between the sun and the Earth. If the sun went supernova, it would take us eight and a half minutes to find out.

If that's the case, the oldest light source we can see would do the same, correct?

I have no idea what you're saying here.

Then, you say, prior to that, there was a time when there was no visible light, and we have detected this. With what?

No, I didn't say that. In fact, I said that there was a time when the entire universe was filled with high-energy (that's going to be in the visible spectrum and probably above) photons (particles of light) and electrons. As the universe expanded, these particles cooled off; some coalesced into stars and, later, planets. Though these particles cooled, they are still found everywhere in the universe, just more spread out than they used to be.

Now, as you may or may not know, the visible spectrum makes up only a small fraction of the entire electromagnetic spectrum. At the high-energy end is ultraviolet light, X-Rays, and gamma rays. At the low-energy end is infrared light, microwave radiation, and radio and television signals. At this point, the high-energy photons from the early universe have cooled down into the microwave level, and they were detected first in 1965 by a radiometer designed to conduct radio astronomy (measuring low-energy transmissions from various celestial bodies). The scientists detected this background noise that they couldn't account for, and after trying to find out what was causing it, discovered that it almost perfectly fit the predicted value of the cosmic microwave background radiation. Subsequent studies, specifically the COBE satellite, have made more detailed measurements of the background radiation.

And then, in the beginning, there was this infinitely dense ball of energy, matter, and space. Didn't earlier theories suggest that prior to the big bang, a prior universe may have imploded into this ball? What have we learned to make this impossible? If it isn't impossible, would we be able to see light from that universe?

The idea that there might have been some previous universe is pure speculation, based on a once-popular oscillating model of the universe. The idea was that, given enough mass, eventually the gravitational pull would slow, stop, and reverse the expansion of the universe, resulting in a Big Crunch event which would bring the universe back to its pre-Bang state. Unfortunately, this doesn't seem to be the case. Modern cosmological models show that not only is there not enough mass to slow and stop the expansion of the universe, but there is some energy causing the expansion to accelerate. The modern eschatology is that the universe will die a "heat death," where the entropy will increase to a maximum, resulting in a generally homogenous, lifeless universe.

The reason we wouldn't be able to see light from the prior universe is that those photons, like everything else, would have been crunched back into the ball at the beginning. There's no space for that light to travel through from the previous universe, the very fabric of space would have been crunched into that singularity.

It's very, very tough to think about this sort of thing, because there is no good analogue in our experience to this.

What percentage likelihood would you personally give to the Big Bang theory? Knowing that we have almost no knowledge of how clouds work around our own little planet, can you imagine giving it a likelihood above .1 percent.

You keep bringing up clouds, and I never quite know why. We know the physics of how clouds form, we know the physics of their movement and travel, we have a whole science devoted to the study of clouds and other weather effects, called meteorology. We know what they're made of, we know what different types of them are and what properties are specific to each type...what is our huge ignorance regarding clouds?

But, to answer your question, yes, I'd give it a very, very high likelihood. Somewhere in the 90% range. First, it explains why everything in the universe is moving away from each other. Second, the predictions made by the theory have not only been confirmed (the real test of a theory) but spectacularly confirmed. It is very rare in science for the measured numbers to match as closely to the predicted numbers as the measurements of the CBR.

There are a lot of factors in weather that make quantitative measurements difficult (check out chaos theory sometime). Out in the vacuum of space, those factors are minimal. We can get quite a lot more in numbers and measurements about radiation in the universe, a relatively simple thing, than we can get from the very complex, interconnected set of laws and circumstances which govern weather.

Which is, of course, assuming I have the foggiest clue about what you're saying with this cloud stuff. I'd really like to see your sources for that...I mean, really, clouds and astronomy are pretty unrelated. It's like asking "how reliable is the theory of gravity, given how little we understand about the human brain"?

Randy Kirk said...

Pretty interesting about the early history of the universe as currently understood.

Here is my problem which probably deserves a post of its own, and goes to one of the most basic ideas of this entire blog. What is and isn't evidence, and how do we evaluate it?

You give an 80% likelihood to an idea that deals with beginnings of the entire universe that must be interpreted through the vastness of time and space using instruments and techniques that are less than a generation old. A supposed 2000 scientists are giving a 90% likelihood that we are going to be experiencing a 3 degree raise in temperatures over the next 50 years, using computer models that can't even be used in retrospect to predict current weather patterns.

Yet, when I say that billions of people self-report a perception of relating to God, you say that is not evidence at all or less than 1% likely to be true. This makes it hard for us "laymen" to put much faith in many of the conclusions of scientists.

Bernardo said...

"What is and isn't evidence, and how do we evaluate it?"

This is evidence:

http://en.wikipedia.org/wiki/COBE

I mean, really, how much better than this...

http://lambda.gsfc.nasa.gov/product/cobe/cobe_images/firas_spectrum.jpg

... can you get? From here: "The FIRAS data match the curve so exactly, with error uncertainties less than the width of the blackbody curve, that it is impossible to distinguish the data from the theoretical curve. These precise CMB measurements show that 99.97% of the radiant energy of the Universe was released within the first year after the Big Bang itself. All theories that attempt to explain the origin of large scale structure seen in the Universe today must now conform to the constraints imposed by these measurements. The results show that the radiation matches the predictions of the hot Big Bang theory to an extraordinary degree."

Looking at COBE data and doubting the Big Bang is like looking at fossil data and genome data and doubting evolution, or looking at geological data and doubting that the earth is billions of years old: Only a deceitful God would set things up in such a way that so strongly suggests mistaken interpretations.

Randy Kirk said...

Let me the real skeptic. The original formula's turn out to be wrong because of incorrect assumptions. The incoming information from the telescopes is skewed by some aspect of the information retrieval system, the way the readings are effected by time travel, or 1,000,000 aspects of the universe that we can't even possibly know.

Example, we just learned new aspects of how solar flares work on the sun that blew the scientific communities' collective mind. One simple system 8 1/2 minutes away that has been studied with great care. All changed. 80% certainty. I'd say almost 100% certainty that within 20 years we will find out we were completely wrong, and in another 20 we will have another theory or go back to this one. I'll be in the ground by then, so I won't be able to collect on the bet.

bernardo said...

So, yeah, our models aren't perfect, and no one claims that they are the exact truth. But observation allows us to explore the areas where our models are least accurate, so we can improve them. And when a model matches all observable evidence as closely as any instrument can detect - even when a new instrument is designed specifically for the sake of observing, for the first time, something that could make or break the validity of a model - then it's pretty crazy to think that the core of the model completely misses some important aspect of reality. Not completely crazy, but pretty crazy.

Here's one key difference between the solar STEREO observations and the Big Bang COBE observations: In the solar ones, they went "We think that the stuff that comes out of the sun is made by mechanisms A, B, and C, so let's go have a closer look to check", and they were wrong. In the Big Bang one, they went "We're pretty sure that the stuff in the universe came from mechanisms A, B, and C, but if this is the case, then this particular radiation pattern should also be observable, so let's go look for it", and they found it. So, yes, there could be other mechanisms behind the observations they made. But the fact that the scientists went looking for such a particular distribution of radiation, and found it so exactly without ever having looked before, is strong evidence for their model.

When was religion ever this powerfully predictive?

(And if your answer is "biblical prophesies"; Sure, there's a lucky guess or two in there, but most biblical prophesies are only prophetic when taken out of context, and most of the remaining ones were edited afterwards to get stuff right, and that's not counting all the ones that DIDN'T come true).

Randy Kirk said...

Personally, I would not compare Biblical prophesy to scientific analysis and prediction. As often stated here, I am a great fan of science, and fully appreciate the benefits of the knowledge it produces.

On the other hand, I think I have a higher level of skepticism with regard to the claims of science than do most who call themselves scientists. I have used hyperbole in this blog with regard to some of the excesses and unethical aspects of science. I know that there are many scientists that, to the best of their ability, acknowledging their humanness, taking into consideration the unique lens through which they view things, do their very best to stay neutral in their analysis. Having said that, I just think it is harder, when you are immersed in a certain culture, to avoid the conflicts and the distortion caused by that immersion.

Of course, this would then apply to those of us immersed in the Christian culture, as well.