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Another physics pop quiz(27 posts)

Another physics pop quizDougSloan
Jul 5, 2002 6:02 AM
Some may have thought the last one too easy. How about these questions?

1. I cannot get a grasp on the concept of "infinity" in the physical universe. What does it mean?

Subparts:

a. What lies beyond the physical matter of the universe (or, is it truly infinite?)?

b. What was happening before the beginning of time? (and will there be an end? - if so, what happens after that?)

c. Do we simply lack the language and concepts to describe the true nature of the universe (despite Stephen Hawking making an excellent attempt)(but I can't accept this cop-out)?

I really want to know.

Doug
that's why we have religion (nm)ColnagoFE
Jul 5, 2002 7:05 AM
I don't remember the concept of infinity explained nmDougSloan
Jul 5, 2002 7:27 AM
no...butColnagoFE
Jul 5, 2002 8:31 AM
It's all covered by faith in organized religion. Basically there are things we will never know and that could be considered god...infinity...whatever. It's part of god's plan and all will be revealed when you kick the bucket. not that i believe any of that, but religion has long been used to "explain" things that science has yet to explain or can't explain.
answer: chronosynclasticinfudibulationAllisonHayes
Jul 5, 2002 8:51 AM
the ability to be everywhere at all points in time

also, chronosynclasticinfudibulation can be explained by quantum mechanics and Heisenberg's Principal of Uncertaity

As things approach zero, they tend to approach infinity and physics as we know it falls apart.
An attemptMcAndrus
Jul 5, 2002 8:53 AM
1 - Infinity is a mathematical concept used to explain the thing that can be explained in no other way. We are unable to understand the endless so we define it as the anti-thesis of something else. The opposite of finite (which we grasp quite well) is infinite. In mathematics it is a useful concept. The result of a number divided by zero is called either "undefined" or "infinite."
1.a - We do not have any technology to determine what is beyond the universe. As far as I know we do not even have any theoretical physics to guess at it.
1.b - See 1.a. If there was a beginning then there logically will be an end.
1.c - It more than lacking a language, it's lacking the conceptual ability to even ask the questions correctly. I believe we are truly and ultimately unable to answer such questions. To imply the existence of something before the universe and something after the universe implies existence and some variation on the universe we know (more later).

The Judeo-Christian version of this simply says, "In the beginning, God created...." God was before and God will be after. There may be merit to the position that religion is an attempt to explain the unexplainable.

As I understand it, our universe may be one of three types: steady-state, expanding from the big-bang, expanding and contracting from repeated big-bangs. The prevalent theory (and you seem to have read Hawkins) is the expanding big-bang. I think the evidence is still incomplete.

I forget what the number is but I know some physicists have tried to calculate the size of the universe based on the date of the big-bang and the speed of expansion since. This would mean the universe is finite but we may never be able to find its limits.

When I want to really mess up my own brain without beer, I ponder this: where does the matter consumed by a black hole go? Are there white holes? Does the matter slip into the black hole and reappear in a white hole? Does the destruction of matter in a black hole in fact create a new big-bang in some other universe?

Jeez, Doug, I was just trying to spend a quiet Friday at work, slipping into the weekend and you go and ask questions like this. Have you no mercy?
it's really boring here at work today? (nm)ColnagoFE
Jul 5, 2002 9:00 AM
I can respond to this one, at leastDougSloan
Jul 5, 2002 9:14 AM
I can't even respond to Allison's post. Other than some chemical names, I think that may be the first word I've seen that I can't pronounce, no matter how hard I try. :-)

There is something to that "ask the right question" issue. Maybe time or the 3 physical dimensions are not what we think they are (unified theory?). In other words, in a world with only square blocks, how can we construct a sphere?

A cyclic universe is much easier to comprehend than a finite one. At least is solves the before and after issues. Scientists are still wrestling with the rate of expansion and total mass/gravity issues to tell whether it will do the big squish or forever expand.

Matter in black holes doesn't go away; from what I understand, all the space between the particles goes away. However, I saw a documentary about this, and they were discussion some type of energy emissions from black holes in the center of galaxies radiating out from what would be the axles if the galaxy were viewed as a bicycle wheel. Further, they have determined that all galaxies have black holes at the center. Very fascinating.

Black holes are hard to imagine. I think I heard something like the mass of a thousand suns could fit in a tablespoon of black hole matter.

If the universe has a quantifiable size, then what is beyond that? Just nothingness? Do you reach the "other side" like a sphere? I can't get a grip on that.

I'd love to be a theoretical physicist, if I were smart enough. The math gets really hard.

Doug
if 'beyond physical matter', then it isn't a physics question! nnova
Jul 5, 2002 9:10 AM
m
metaphysics? (nm)ColnagoFE
Jul 5, 2002 9:20 AM
sure it isDougSloan
Jul 5, 2002 9:28 AM
Empty space (if there is such a concept) and energy are within the realm of physics.

What I mean is, once you reach that last planet circling that last sun in the last, outermost galaxy, then what? Do you look one direction and see absolutely nothing, and in the other see billions of stars and galaxies?
edge of expansionmaricio
Jul 5, 2002 10:28 AM
If you were on the edge of the expanding universe, yes you would see nothing in one direction and billions of stars in the other.
Universe: Beige, not Turquoisenova
Jul 5, 2002 11:27 AM
http://www.wired.com/news/technology/0,1282,50930,00.html
what does "absolutely nothing" look like?ColnagoFE
Jul 5, 2002 11:46 AM
by definition it is not empty space.
what does "absolutely nothing" look like?maricio
Jul 5, 2002 10:37 PM
Just because it is not empty space doesn't mean it doesn't look like empty space.

It probably looks like rainbows with leprechauns bouncing around or something.
Throwback to dark matter. But better.Leisure
Jul 7, 2002 2:47 AM
Long postulated and sometimes still batted about.

The nice thing about the end of the Universe where absolutely nothing exists is there's no way to actually get there and figure it out. The end of the Universe is travelling outward at the speed of light (or, in theory, faster?) and is defined by the light that was first emitted at the Big Bang. Nothing can catch up with it. When you sit on the last planet on the last solar system, that light is still moving outward relative to you at the speed of light and has been doing so since the beginning of definable time. It gets worse. The individual photons out there are, by definition, moving away from each other at the speed of light. So one photon that we might measure as moving outward any infintessimal distance in front of the other is, relative to itself, moving farther ahead of the other at the speed of light, and has been doing so since the beginning of time. Which makes the universe a cute little sphere from which you can never definably escape. Black holes are postulated to be a way around it, but who knows.

I suppose it's kind of fun to postulate about what's out there, though. I figure it is only what it is which is absolutely nothing, with no definable dimension, and the size of the universe extends only as it expands to define the properties of new space. I wonder if they'll ever discover that the universe/space is defined by an inert wave-particle medium on which resonant energy either aggragates into what we know as mass or bounces about freely constrained by the properties we ascribe to light.

I'm just bullshitting about that last part by the way. I don't claim to be any sort of specialist in the subject. I think it's more fun to let imagination run wild in these subjects than to have to actually be responsible and figure out what's empirically/theoretically viable.
re: Another physics pop quizmaricio
Jul 5, 2002 10:16 AM
a. The universe is like a balloon expanding; our physical universe is not truly infinite. I guess there is a vacuum of nothingness beyond the expansion. Some people think it's bold to believe our universe is the only one though.

b. No one understands the beginning of the universe until about 10^-43 of a second. To describe the first instant, we need a theory that links general relativity with quantum mechanics. General relativity describes the structure of spacetime (large-scale) and quantum mechanics describes subatomic particles.

In the first instant of time there were very large random mass and energy fluctuations (that we can't explain).

What was happening before this, where did this mass-energy come from? Nothing...? Lends support to creationist theories in my opinion.

Will there be an end?
Yes. This is a multi-part answer as there are different things that can occur.

Some people believe the universe is closed and that the gravity that pulls everything together will eventually cause expansion to stop then reverse. This would eventually end everything in a "Big Crunch".

If the universe is open and will continually expand forever, the end will be gradual. In the universe there is a star-gas-star cycle. As this cycle continues, more matter will be locked up in stars, planets, neutron stars, black holes, etc, and the creation of stars will slow down and stop. In about a trillion years all the stars would have died (our own sun will die in about 5 billion years). Infrequent collisions between objects will be the only new activity in the universe, flinging some objects further from all other objects out in space, and causing other objects to lose energy and fall to the galactic center forming a gigantic black hole.

The universe will consist of black holes containing as much as a trillion solar masses, immensely far away from each other, and other scattered frozen chunks of planets, and stellar corpses.

If that's not enough, there are theories that protons have a half-life of 10^32 years or so and all matter will disintegrate into radiation and subatomic particles by the time the universe is 10^40 years old.

The black-holes themselves are predicted to slowly evaporate through "Hawking Radiation". Trillion solar-mass black-holes would be expected to evaporate in about 10^100 years.

After this, the universe would only be individual photons and sub-atomic particles immensely far apart.

This would be the end of time, as nothing would ever change or be abe to cause change; although, there are people that believe in a rebirth of the universe as well. I don't know very much about this.

c.
My understanding is that most scientists believe that the true nature of the universe can be understood quite well, except for that first 10^-43 of a second of time where very little can be explained.

I am no astrophysicist, but the universe does interest me. I took an Astronomy class that gave me a lot of insight into what is believed of the universe. I am amazed at how much of it we know and can understand. It really is fascinating.

I hope my response helps.
coolDougSloan
Jul 5, 2002 10:29 AM
Good info.

What if they are incorrect about the fundamental assumption/observation that the universe is expanding? Would that throw everything off? Or, is it really beyond question at this point?

Doug
Expansionmaricio
Jul 5, 2002 10:41 AM
Some people do believe that the universe is not, overall anyway, expanding.

This would mean that we're moving towards a "Big Crunch". That, as far as I know, doesn't throw too much off though.

Einstein believed there was some other force that is pushing things apart, aside from the initial Big-Bang; and that the universe is actually accelerating as it expands. I can't remember what he called this force.

There apparently has been evidence recently to support this belief.

There is indeed a lot we don't know, but what we do know has a lot of scientific and physical evidence behind it.
ExpansionMcAndrus
Jul 5, 2002 11:13 AM
Maricio is right that the universe is expanding and I can think of no reputable evidence to suggest otherwise. When Hubble developed the Hubble Constant in the 30s (or 20s?), he proved the expansion by observing the red-shift of the light being emitted by objects moving away from Earth.

Hubble's Constant was actually more of a shock to cosmologists than was Einstein's Relativity. Until then, the prevailing theory was a steady-state universe wherein objects moved around a lot but the universe as a whole was stable. It took a lot of physical observation but very little imagination to look at Hubble's Constant and extrapolate that a center-point for the expansion must exist.

The expansion was confirmed in the 1960s when the first radio-astronomers (I forget the names) discovered the 3 degrees (Kelvin) radiation that exists throughout the universe and is a remnant of the big bang.

The continous-expansion vs oscillating question will be answered when physicists can (or cannot) discover if enough black-matter exists to create the gravity necessary to pull the universe back together once it's reached the limits of its expansion. I believe they've established that there is not enough normal matter to create sufficient gravity to cause an oscillation - for the universe to reverse back to a singularity.

Maricio also mentioned a point I'd forgotten, entropy. Even in the continously expanding universe, eventually time will cease as everything falls apart at the molecular level.

And what's at the edge of the universe? I'd vote for nothing: at least nothing we can comprehend.
ExpansionLeisure
Jul 7, 2002 2:10 AM
The most recent estimate I heard was they think the universe only has about 10% of the mass required to cause a Big Crunch. I heard elsewhere that they were still postulating whether or not neutrinos carry a virtual mass, and if they indeed do they could make up the difference.
creationist theory is not science...ColnagoFE
Jul 5, 2002 11:51 AM
it is just a way to explain the unexplainable...just as plausible might be to say the easter bunny created everything.
Meet your maker sonny....AllisonHayes
Jul 5, 2002 1:02 PM
re: Another physics pop quizSkip
Jul 5, 2002 2:11 PM
OK, here's one for you.

Imagine that aliens landed from the far reaches of the universe, and said that they know the answers to the questions you ask, but that we (the human race) are not intelligent enough to even grasp the concepts - that it would be like trying to get ants to understand the theory of relativity.
knowledgeDougSloan
Jul 5, 2002 3:00 PM
If they were truly intelligent, they would be able to communicate it to us in simple terms. At least we possess the ability to think and communicate, unlike ants, which are pretty much instinctual, aren't they? (I realize they communicate basic things, but not abstract concepts.)

I'd at least ask them to try.

doug
knowledgeSkip
Jul 5, 2002 3:46 PM
Could you explain to the ants, in simple terms, and have them comprehend the theory of relativity? I don't know whether ants think or reason, but they definitely have the ability to communicate, and their social order is very well developed. I would surely hope that we (humans) are more intelligent and advanced than ants; we possess the ability to think and communicate, yet I can't speak ant (in any language, tongues, mental telepathy, energy, chemistry, body language, etc.). Even if we learned some means to communicate with ants, would/could they understand it? My analogy was only to try to point out the vast chasm that may exist between our most intelligent (maybe even our collective, human, intelligence) and a far superior "mind"; that our perceived ability to be able to comprehend anything, if it was just explained "right" or "correctly", or in terms we were familiar with, etc., may be beyond our comprehension - hard to take, I know. We all want to assume that we are the top of food chain, most intelligent. But when you start thinking on terms of universal scale, and think that "we" are as good, or close to, as good as it gets, or even that we are the only intelligent life in the universe - we are pretty pathetic. If we can't even acknowledge or perceive the possibility of such a chasm of intelligence/knowledge/wisdom, how could we ever hope to understand the concepts?
Uh, well, what I tend to think about...Leisure
Jul 7, 2002 4:00 AM
1. I figure "infinity" to only exist outside of dimensional constraints. Any dimension by definition invokes the existance of boundary conditions, meaning an end, a limit beyond which you cannot go. Infinity cannot exist in dimensional space because it could only do so infinitely (even in the condition of infinite space), which would rip apart that space. So answering 1a., the universe cannot be infinite in any way, shape, or form. Infinity may exist, but it would not do so within a definable space. I can't prove any of this by argument, but there are examples.
- Black holes are bodies of mass that exceed very high densities (they don't have to, but we are used to thinking of them that way). There is no way they can definably reach infinity, they simply exceed the limits of definable space-time and rip it apart.
- Light defines the fastest velocity you can attain. Attempt to surpass it, and space and time will dilate to prevent you from doing it. You therefore cannot reach infinite speed.

I figure infinity is probably solely the domain of God (or whatever infinite force you want to hypothesize) and does not manifest in any other form.

1b. Before the beginning of time, there was no time. It was not a defined dimension and therefore nothing was happening. That is the boundary condition that constrains the beginning of the known universe in all its dimensions, and those dimensions as we know of them didn't exist beyond that. Whether or not this corresponds to the Big Bang or something else is anybody's guess.

1c. Sometimes I think we make life more complicated than it needs to be. Sometimes nothing is really nothing. It defies being defined because a definition is itself something, and we have thus made something out of nothing.