What is our universe expanding into?

  • Thread starter Robert100
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  • #26
Expansion of Universe

The CMB photons 'cool' simply due to redshift, which is caused by expansion alone (ignoring the Reese-Sciama effect).
That is why I had stated that this is not as simple a question as it appears because I knew I would be opening a new debate.

Cooling of 'photons' due to redshift cannot be explained through redshift because universe at smaller scale is neither homogenous nor it is isotropic.

I do not want to enter into a new debate on big bang theory because it would be sheer waste of time. At best, big bang theory can only be described as highly imaginative.

We can accept the premise that a blackbody in pure thermal equilibrium may have temperature (Photons are not supposed to have temperature) but to state that photons are the source of CMB radiation would be asking us to take our imagination beyond the realms of science.
 
  • #27
Maths in Physics

We must have read different posts. He made it clear that answers could not be given to those who asked questions, except for those already studying doctoral level physics. He only gave a handful of sentences for explanation, something totally insufficient even for a topic in 9th grade physical science, let alone graduate school level physics. And people recently implied that I am anti-relativity crank. From whence does this anger come? (Yes, they used the word "crank", which is only used in physics to discuss the crazies who think they disproved relativity, QM, etc.)

In any case, don't overlook the point of my most recent letters. They were about how we should treat each other on this forum. Our purpose is mutual support and education, right? Conside the recent topic I started on "How can empty space expand"? There was no anger, no charges of misrepresentation or claims that the question implied "crank" views. Rather, people answered with references, and tried to explain the basic concepts. That is par for course here, which is why this is the only physics forum I frequent on any regular basis.

In any case, I totally agree with you that we should not divorce physics from math. I don't believe any such thing.



I totally agree with everyone here on this. I certainly am not claiming to have found a hole or error in relativity! Please re-read my earlier postings.

In any case, don't make this a choice between light-weight pop science without content, or balls-to-the wall tensor calculus. There is quite a lot of room in between. I remember being at PASCOS 91 (Particles and Strings Conference) at Northeastern University, Boston, MA, listening to talks by Ph.D. physicists for Ph.D. physicists, including Stephen Hawking. The arcane points had serious math, sure but guess what? Everything was also discussed in plain English terms, with diagrams and analogies. This was not some pop convention open to the public. It was hard core.

But a physicist needs to explain in English, with diagrams, explanations and analogies, because not all physicists have the same background. An expert in solid state physics could be almost as lost in the math of string theory as an Ballet dancer.

Recall your reference for me to read http://www.arxiv.org/abs/0707.0380
"Expanding Space: the Root of all Evil?" by Matthew J. Francis, Luke A. Barnes, J. Berian James, Geraint F. Lewis

This is a perfect example of a comprehensible answer to a very complex physics question. While an analysis of the question requires serious math, the main point was zeroed in on using simple logic, in plain English arguments. For educated laypeople, especially people with a BS in physics or engineering, this article is certainly comprehensible.

Now, you are correct on this point when you refer to the many low level popular texts out there that give the reader the illusion of comprehension, yet actually teach the reader very little. Sadly, I have concluded that even some of the popular works by Stephan Hawking fall into this category. His works explain quantum mechanics, relativity, string theory, time itself, the creation of the universe, etc. Yet if you quiz an intelligent reader on these subjects after they have read his books, you'd find that they have no idea what they are talking about. It seems to me that his books cover far too many topics in too short a space to really explain anything well.

Most pop science books by others give the illusion of knowledge, without true conceptual understanding.

Yet there are fine physics books out there that allow intelligent readers to understand the basic ideas of complex subjects. Richard Feynman's excellent QED isn't "QED for idiots". Most working physicists have never studied QED, and thus most wouldn't understand it all without Feynman's work. It does not commit the sin of oversimplifying so much that it is wrong. It actually gives you a way to understand what is going on. Of course this is done without the math, so that the reader obviously cannot do any problem solving, or make his own predictions, or use it to find limitations in other areas of physics.

Consider special relativity: I have used (advanced) high school physics books that are useful for explaining this theory!

Consider general relativity - Bernard Schwarz's "Gravity from the Ground Up" (Cambridge Univ. Press). This is certainly not "pop science". What about Lee Smolin's excellent "The Trouble With Physics", which allows even laypeople to understand the criticisms made against the trend to accept string theory as the only theory of everything?

I'll save the big guns for last: Taylor and Wheeler's "Spacetime Physics". You don't even need to understand all the math in the book. The first three chapters alone, with graphs, pictures, analogies, and a few simple ideas turn our intellectual world upside down. We suddenly can see for ourselves that measurements which we believe to be invariant can, in fact, vary, when looked at from another reference frame or coordinate system. We learn that the basics of special relativity can be derived from common sense analysis, if one only asks the right questions in the right order.

These books assume that physics is not only for physicists who specialize in relativity and quantum mechanics. The authors understand that educated laypeople - and physicists in other areas of physics - want to understand these great ideas in a meaningful way, and not in the pop sci way that so many inferior books present. That is usually the attitude on these forums as well.




I agree with you. No one should imagine that learning a subject at the level of the books I have mentioned allows someone to do this. I am thus confused by the way that people have begun attributing this position to me. Some posts here seem to have been written by people under the impression that I believe that I have found a flaw in general relativity. Yet I have no such belief at all.

Marcus writes:


Well, I don't get this. What he calls "Robert's theorem" is a part of basic geometry. It always has been, and always will be. In both two- and three-dimensional classical geometry, expansion by definition always implies the existence of a space into which the expansion takes place. I believe that it was Marcus himself who said this earlier - From the ancient Greeks until 1850, this was always accepted as common sense, true by definition. However, around 1850 people began to consider new geometries, and new ways to describe geometries, both static and dynamic.

Marcus stated quite correctly that there are ways to describe the expansion of the universe "from the inside", without any need to reference any volume outside of what we are describing. That's true - and I never said otherwise. But this doesn't mean that everyone in the world (including me) is now suddenly a "crackpot" because we note that as we blow up a balloon, the volume of the room that we're in (outside of the balloon) is now less. As the balloon expands, the space in the room outside the balloon decreases. This proposition is still true.

The question is whether or not this can meaningfully be extended to the entire universe, to which people here say "No, it shouldn't." I asked why not, and no one answered in polite fashion. Instead, I was lectured to, and told "Just believe the math". That is nonsense, and against the philosophy of teaching, against the philosophy that most of us here usually present.

My real question has always been the same, and only recently did one person finally "get it". (That person being Marcus.) I didn't ask about the technicalities of tensor calculus integrals. Rather, I asked:

(a) is the math proving that no outside can possibly exist?

(b) is the math, at least, strongly suggesting that no outside can possibly exist?

(c) is this math actually silent on the issue? That is, the math only describes the changing volume of the universe, without need for us to discuss any larger volume it could conceivably be embedded in?

At this point, it now seems clear that everyone agrees with (c). And this is what I have held to be true all along.

Given that (c) is true, I am asking "What do you think this implies"? And pow! Suddenly I am perceived as an anti-relativity crackpot. So sad. I am reminded of the way that physicists were attacked when they asked "But what does the wavefunction mean in quantum mechanics"? Until 20 years ago, most physcists responded "Shut up! It doesn't mean anything! Just calculate". Today, of course, the great majority of the physics community reazlies that this was a gross error, and that in fact people should be encouraged to ask such questions.


Robert
I think we need to discuss the role of maths in physics. Theories of physics are supposed to be the outcome of the study of nature and are not supposed to be based on mathematical equations.

Maths enters the scene after the theory but now we have mathematics giving us new theories. I have explained in my earlier post that 'Photons' having temperature is against all known properties of photons but mathematics allow the possibility of photons having temperature. This is simple abuse of mathematics. mathematics is not a 'creative' science. It is not supposed to generate new ideas but is only required to convert what we can say 'Theoretical Physics' into 'Applied Physics'.

We are so lost in the mathematics of relativity that we have forgotton the theory of relativity.

Big Bang theory suggests that 'time' and 'space' expanded for a brief period. Go back to theory of relativity and try to get a clue that would back this statement.

Einstein definitely would not be at peace wherever he might be.
 
  • #28
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Robert100 said:
...including Stephen Hawking. The arcane points had serious math, sure but guess what? Everything was also discussed in plain English terms, with diagrams and analogies. This was not some pop convention open to the public. It was hard core.
Really? That doesn't sound like Stephen at all... :smile:

On a more serious note, I have to say that I found shoehorn's explanation both correct and patient. A grade-school translation of what he said would perhaps be:

Lengths, areas, and volumes all depend on the ruler (the metric) one measures them with. General relativity states, very loosely, that over time the rulers one uses to measure such things must change. As a result, lengths, areas, and volumes all change over time.

This property does not depend on "higher-dimensional space."
There are plenty of points one could quibble with in there but this, in essence, is what shoehorn was getting at. The only difference is that he wished to be precise about what he was saying, presumably for your benefit. Given that he provided an excellent explanation of why your initial question was misguided, and given how he also provided an explanation of the correct way to ask the question, I think you should be grateful instead of accusing him of attacking you.

Just my two cent.
 
  • #29
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"Lengths, areas, and volumes all depend on the ruler (the metric) one measures them with. General relativity states, very loosely, that over time the rulers one uses to measure such things must change. As a result, lengths, areas, and volumes all change over time.

This property does not depend on "higher-dimensional space."

What do you meen when you say the ruler changes. Isn't a unit only prescribed by humans for purpose of measurement by comparison.

I'm probably just ignorant, but I can't see how the length of fictional units can have anything to do with volume or expansion.

1/2+1/4+1/8.....=1 Infinate midpoints can be crossed in a finite unit.
 
  • #30
marcus
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What do you meen when you say the ruler changes. Isn't a unit only prescribed by humans for purpose of measurement by comparison.
...
TR345, I never heard of the ruler changing (as part of GR)
it is only that distances increase. the UNITS don't have to be changing

the distance function is called the "metric". that is what changes.
the units (e.g. the ruler) should probably not be thought of as changing
 
  • #31
Time dilation and length contraction are the concepts arising out of Lorentz Transformations. We may discuss in brief Max Born's clarification...

max Born explains that concepts arising out of Lorentz Transformations are only a way of regarding things and cannot be construed as any change in physical reality and hence are outside the scope of law of causality.

One question that arise out of this explanation is, does it reduce Lorentz transformations and theory of relativity to of mere philosophical value? As physicists, we can only be interested in the study of physical reality and the factors that bring about a change in the physical reality.

It would also be important to mention here that length contraction due to cooling of a system (like the metallic structure at CERN that has contracted by 3mm/meter) is explained by different principle. Lorentz transformations predicts change in the systems due to motion. Relativistic mass is one such change and is one of the most important changes Einstein introduced in his special theory.
 
  • #32
universe expansion

Robert;
You may as well give up this discussion. Trying to "logically" convince a group of mathematicians or so called physics majors, that something has to have a space to expand into is a futile and frustrating effort at best. If you asked a group of mathematicians to prove mathematically that "nothing is everything and everything is nothing" each would come up(given enough time)with a different equation that they would swear is irrefutable proof that this statement is true.
Einstein once said in reference to religious belief versus science;
"The more a man is imbued with the ordered regularity of all events the firmer becomes his conviction that there is no room left by the side of this ordered regularity for causes of a different nature. For him neither the rule of human nor the rule of divine will exists as an independent cause of natural events. To be sure, the doctrine of a personal God interfering with natural events could never be refuted,in the real sense, by science, for this doctrine can always take refuge in those domains in which scientific knowledge has not yet been able to set foot". end of quote.
I fear this argument of universal expansion is one of those domains in which scientific knowledge with all it's mathematical tools has not yet been able to set foot.
However...be assured, there are thousands of logical thinkers out here in the "world beyond math" that have asked the same question you have without getting a logical answer. How laughable that with our meager minds with it's meager tools sitting inside a "bubble" can hope to explain what is happening outside this "realm". When all their mathematical tools and ordered physics fail them...well...the next step for their minds with well defined tools and borders will be to add a creator or god to their equation for they cannot perceive that we humans can exist without one or the other.
No matter how hard you try, these great "genius's" in this forum will never be able to wrap their minds around the "logical thinking" that you have displayed.
You are not alone.
(forgive the emphatic number of quotation marks).
...Rationalism101...
 
  • #33
Robert;
You may as well give up this discussion. Trying to "logically" convince a group of mathematicians or so called physics majors, that something has to have a space to expand into is a futile and frustrating effort at best. If you asked a group of mathematicians to prove mathematically that "nothing is everything and everything is nothing" each would come up(given enough time)with a different equation that they would swear is irrefutable proof that this statement is true.
Einstein once said in reference to religious belief versus science;
"The more a man is imbued with the ordered regularity of all events the firmer becomes his conviction that there is no room left by the side of this ordered regularity for causes of a different nature. For him neither the rule of human nor the rule of divine will exists as an independent cause of natural events. To be sure, the doctrine of a personal God interfering with natural events could never be refuted,in the real sense, by science, for this doctrine can always take refuge in those domains in which scientific knowledge has not yet been able to set foot". end of quote.
I fear this argument of universal expansion is one of those domains in which scientific knowledge with all it's mathematical tools has not yet been able to set foot.
However...be assured, there are thousands of logical thinkers out here in the "world beyond math" that have asked the same question you have without getting a logical answer. How laughable that with our meager minds with it's meager tools sitting inside a "bubble" can hope to explain what is happening outside this "realm". When all their mathematical tools and ordered physics fail them...well...the next step for their minds with well defined tools and borders will be to add a creator or god to their equation for they cannot perceive that we humans can exist without one or the other.
No matter how hard you try, these great "genius's" in this forum will never be able to wrap their minds around the "logical thinking" that you have displayed.
You are not alone.
(forgive the emphatic number of quotation marks).
...Rationalism101...
Thanks.

I certainly do not treat it as a case of we against them. I am a part of them and hope you are also in the same boat. Development of science or for that matter development of any field of knowledge is not possible by closing down the possibilities. A scientist has to be like a chess player who looks for new openings all the time but he also goes back and studies previous games to see if someone has made a mistake or had a missed a promising line of play.

As far as acceptance of certain facts is concerned, you would agree with me that string theory is devoid of any scientific facts. It's argument is that possibility of existence of strings and extra dimensions cannot be ruled out and existence of extra dimensions can resolve lots of problems of theoeretical physics. With this logic one can propose anything. Science is no longer what it once was, physics definitely is not. Understanding nature is not the priority of some physicists, winning noble prize is the only objective they work for,

I certainly believe that Einstein's arguments presented by you are not correct. These arguments come from the wrong belief that if I cannot understand something then it cannot be understood by anyone. We react to the words and not the concept.

If isotropic and homogenous CMBR shows anything then it shows that universe functions as one unit and that entropy is an active process in the universe and different parts of the universe are in communication with each other. Some scientists fails to realize that in a universe where matter is constantly getting converted into energy, if CMBR is isotropic then some mechanism has to be in place that ensures that energy distribuion is equitable and that with such equitable distribution it is impossible for CMBR anisotropies to exist for such a long time. CMBR anisotropies can only be result of presence of matter and energy that we cannot notice at present due to our observational limitation but I was the first person to predict that dark matter and dark energy must exist even outside the galaxies but as you would expect no one was willing to buy the argument. However, it has now been established that dark matter and dark energy exist even outside the galaxies (independent of baryonic matter). Some scientists are still not willing to accept it even though international team that had reported it has released related data and pictures.

Most of the scientists have started realizing that the current view of the nature is not taking them anywhere but do nto know what to do. It is in such frustration that they have to explore such wild ideas as string theories.


You probably have heard the story 'The Emperor's clothes' but I will still tell it here. There was an emperor who was obsessed with new expensive clothes. Two gentlemen walked into his capital and let it be known they were weavers and could design the clothes that would be invisible to a person who was unworthy of his office or who was unusually stupid.

Emperor summoned them ordered that they weave such clothes for him. They demanded that since clothes were very expensive and they needed their design to be a secret therefore their project should be funded. The funds were granted immediately and two gentlemen promptly set up the looms. They kept on working on empty looms. Eager to know the progress of the work, Emperor sends his most trusted minister to see the progress of the work. Two gentlemen showed the minister empty looms and described most wonderful design and colors of the fabric that was not there at all. Minister was shocked to learn that he was not fit for his office because he could not see anything. He had no choice but to praise the work done by the weavers. He promptly reported the progress to the emperor. On the appointed day, emperor walked into the loom with his minister and a big entourage.

As soon as they entered the loom minister started praising the fineness of the fabric, richness of the colors, and delicacy of design. King could not see anything but had no choice but to approve the clothes. He was promptly made to wear the non-existent clothes and set out on public procession to display the wonderful clothes. Everyone was praising the new clothes of emperor until a child shouted that emperor was not wearing anything at all. Slowly, everyone shouted the obvious fact. Emperor realized that probably they were right but had no choice but to continue with the procession.

We have no choice but to continue with the procession. If scientists take a U-turn then all the Government fundings may be stopped. What do you think would be the outcome of the LHC experiment?

Scientists involved are in a fix. If they report that Higgs Boson has been detected then they are in problem and if they do not declare that they have detected Higgs Boson then they are in bigger problem so the only choice left is to report some sort of positive development and continue the project stating that further tests are required. It happened with LEP and it is happening at Familab and it will happen at CERN.

Hopefully, one day a child will shout that emperor has nothing on.

I agree with what you state about the present condition of physics but if you think that we cannot make a difference then you are giving up too early. Even one person can make a difference and that for me is the crux of the story.

Join hands, have faith in yourself, and believe that you can understand nature. I assure you that you will be able to make a difference.

Best of Luck. Looking forward to your response and response of all like minded persons.
 
  • #34
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Science, mathematics, and philosophy have no way to deal with rational, unbounded, unobserved space. Therefore, the question 'into what is the Big Bang Universe expanding ?' is, at best, difficult to understand or answer.

A better question to ask is 'how does one convert rational, unbounded, unobserved space into empirically bounded, observed space?'

Answer: To convert rational, unbounded, unobserved space into empirically bounded, observed space, simply move some three dimensional matter/energy along with an observer into the previously empty space.
 
  • #35
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Himanshu777, really inspiring to read what you wrote :)
 
  • #36
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(D) There are many more ways that other universes can exist. I refer you to the recent writings of Max Tegmark.

http://space.mit.edu/home/tegmark/multiverse.html

All these possibilites are well known in the literature, yet most people here, and sadly most physics books, seem unaware of these possibilities. I am at a loss to explain this.

Robert
Could it be that a lot of 'modern cosmology' not only is not physics, it is absurd. When someone states that there is no limit to how fast space itself can expand, that someone has entered the world of Alice in Wonderland. Space, itself, cannot expand faster than the speed of light, simply because space does not expand at all. When matter/energy move in space, they can create volumns that can be expressed mathematically, but no actual space has moved. Mathematics is the language of physics only when it speaks empirically.
 
  • #37
The premise of this question is sound. Nothing doesn't exist. It can't. For the universe to expand, it can't be surrounded by nothing. If nothing is even simply a container, or "empty" space, then it is something. Even to refer to nothing as anything means it is something that can be described, which means it's not nothing. Along with Robert100's question, my second favorite is: "Why isn't there nothing"? Here is where the observer or point of consciousness becomes important.... Back to the Q - unless the definition of "expanding" includes an assumption I'm missing, or there are properties associated with distances increasing that I don't understand, I would like to see continued exploration of the question. Robert100, did you move this to the Cosmology forum and are you getting additional responses there? Maybe the question would make more sense if we go back in time: What was here before the Big Bang? It didn't expand into "nothing" - did it?
 
  • #38
russ_watters
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You're right in your characterization of what "expanding into nothing" means, but wrong about the implications for cosmology:

The universe isn't "expanding into nothing", it just isn't expanding into anything. Also, this is a 2 year old thread and really isn't a philosophical question anyway, so I'm locking it.
 

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