Dan B.

Thanks Strange It took me some time, but finally the BB process for infinite Universe is quite clear to me. The explanation is as follow: If the Universe is Infinite, then it was infinite before the Big bang. The BB took place everywhere in space. "To put it another way, the current evidence indicates only that the early universe - the WHOLE universe - was extremely DENSE - but not necessarily extremely small. Thus the Big Bang took place everywhere in space, not at a particular point in space." So, 13.5 BY ago, the whole Universe (Even if it was infinite) was extremely hot and dense. The CMB is decreasing over time. Hence, from about 5000 K, it went down to 2.7 K. However, I still have few questions - 1. What is the expected CMB decrease in the next one hundred years? Can we detect even small level decrease over our life time? 2. If the Universe is infinite today and it was infinite 13.5 BY ago, then how technically it could decrease its temp after limited time frame? As an example, let's look at infinite Oven at 5000K. If the door is open at the infinity, would we get any temp reduction at the center after some time? Can we show/prove any temp reduction in infinite oven?

Do you mean that about 13.5 BY the whole infinite Universe was an infinite hot dense? Based on the BBT, this hot dense has a specific limited size. If it is infinite hot dense (bigger than this limited size) then by definition we need to update the BBT. Why not? I disagree. Infinite Universe means Infinite Universe. If it was Finite Universe, then it must be called Finite Universe. It is a mistake to call it Infinite Universe while it is finite Universe.

If "it needs to have expanded for an infinite amount of time" does it mean that the Big bang must take place infinite amount of time ago? I still don't understand how the current BBT (which its age is limited to only 13.8 BY) gives an explanation for an infinite Universe.

If the Universe is infinite, then by definition it must have an infinite mass. How this infinite mass (everything) could come from the Big bang phase? Is there no finite mass capacity for a bang (even if it is an Ultra Big Bang)?

No I still don't know if the whole 14 Trillion Universe is an outcome of just one bang or several bangs process. In any case, let's take two space spheres at our current real Universe. 1. If the current distance between those two spheres is 10 Trillion LY, what might be the distance between those two spots 13.5 Years ago? If it is still several trillions LY: 2. How could any kind of radiation cross this distance in a 13.5 BY (even if we add the expansion and any other requested feature)? 3. How a single bang or even several bangs could have the same affect on those two different space spheres? I really can't understand this major issue. 4. With Regards to the black body radiation - Based on our understanding the current Universe has no ability to generate Black body radiation. This black body radiation is a product of a single event which took place at a specific time frame (300,000 year old). No less, no more. Therefore, when the Universe was 0.2 BY or even 0.4 BY - it couldn't generate a black body radiation. We get today some sort of an echo from age of 0.3 BY. However, how long this echo could stay with us? How could it still be there in a Universe size of 14 Trillion LY or even infinite? There is no expedite date for this echo?

sorry, but I really can't understand how the BBT works for a 14 trillion LY Universe. As long as we have discussed about the observable Universe (let's say 96 BLY) - the BBT process was perfectly clear. Actually, we call it observable - but in reality we can't see more than about 13 BLY at any direction. Therefore, the maximal Universe which we can see is only 26 BLY (Let's call it visible Universe). Hence, I thought that the Observable Universe is the Maximal universe which could be developed by the BBT process, but we can only see just part of it (visible Universe). Is it correct? In any case, now we discuss about a 14 trillion LY Universe. (Let's call it real Universe) Is there any explanation for the real Universe process starting from t=0 (13.8 BY) ago? Yes, I fully understand this explanation. I couldn't understand this explanation. How a space sphere at a distance of 10 Trillion Light Year away could technically gets the same CMB from the same source as we do? If they could get a CMB from a maximal distance of "about 13.5 billion light years away from them," then by definition our CMB and their CMB must get from different sources. So, could it be that they have a different Big Bang? If so, how many bangs are needed for the whole real Universe? However, diffrent BB meand different CMB. So how a real Universe (14 trillion LY) had been developed out of a single BBT process which took place 13.8 BY ago? any web site?

With regards the Black body radiation: https://ned.ipac.caltech.edu/level5/Sept02/Kinney/Kinney3.html Recombination and the formation of the CMB" The epoch at which atoms form, when the universe was at an age of 300,000 years and a temperature of around 3000 K is somewhat oxymoronically referred to as "recombination", despite the fact that electrons and nuclei had never before "combined" into atoms. The physics is simple: at a temperature of greater than about 3000 K, the universe consisted of an ionized plasma of mostly protons, electrons, and photons, which a few helium nuclei and a tiny trace of Lithium. The important characteristic of this plasma is that it was opaque, or more precisely the mean free path of a photon was a great deal smaller than the horizon size of the universe. As the universe cooled and expanded, the plasma "recombined" into neutral atoms, first the helium, then a little later the hydrogen." Would you kindly explain: How the black body radiation which is a direct product of: "The epoch at which atoms form, when the universe was at an age of 300,000 years and a temperature of around 3000 K " could technically gets to a space sphere at a distance of 10 trillion LY in only 13.5 BLY?

So, the observable Universe is an outcome of the BBT process. Hence, if I understand it correctly, as long as our Universe is as big as the Observable Universe, we have a perfect fit. However, based on the last valid data, the size of our real Universe is much bigger than the observable Universe. Why do you say "if"? Is there any problem with this new data? Somehow we need to give an explanation for a Universe which its minimal size is 150 times larger than the Observable Universe and its maximal size could be even infinite. What do you mean by - "It always been that much larger" If there was something before 13.8 BY ago, than why we do not start the BBT from that moment (even if it was always there)? In any case, if I understand it correctly, the Impact of the BBT is up to a 96 BLY sphere. So how the BBT set any impact on a space sphere at a distance of 10 trillion LY away from us? Sorry that I ask too many questions. I wonder if I'm the only person which asks those questions.

Yes, that is my intention. I have thought about this explanation for the last two days. If I understand it correctly - even if the Universe is 14 Trillion LY, it must had been grown from the same Big Bang. However, I couldn't understand the grow process from 150 mm to this size. I had the impression that the maximal size of the Universe is limited by its age, the maximal speed of mass, speed of light, expansion and some other factors from the BBT. So, is there any technical limit for the Universe maximal size from the BB (in 13.8 BY)? Or can we just assume that as we increase the 150 mm we can get bigger and bigger Universe (For example - from 300 mm the Universe can grow to 28 trillion Light year and so on - without any limit).

Thanks So now as we know that the Universe extends for at least 14 trillion light years in diameter - How can we explain a creation of that Universe size in only 13.8 BY? How the BBT fits to this size of Universe?

Thanks So, as the Observable Universe is about 100 BLY then the minimal estimated size of our Universe is: 15 trillion Light year. Is it correct? Sure. However, can you please elaborate if the speed of light has any affect on the WMAP data as stated:

If the WMAP data means (within very small error bars) that the Universe is Infinite - Why do we still claim that we don't know the size of the Universe? Even if the Universe is finite - do we have any idea what is it's minimal size? What do you mean by "(space isn't quantised)". How this data could affect the size of the Universe?

After all of this discussion, it is clear that our universe is bigger than our observable Universe, but how big? Is it Infinite Universe or Infinite number of finite observable Universes? What kind of data is needed in order to get a final confirmation for the above question? How can we explain the creation of each kind of Universe?

Please look at the following: http://www.astro.ucla.edu/~wright/infpoint.html It is stated that: "The size of the box in each view is 78 billion light years. The green circle on the the right is the part of the Universe that we can currently see. In the view on the left, this same part of the Universe is shown by the green circle, but now the green circle is a tiny fraction of the 78 billion light year box, and the box is an infinitesimal fraction of the whole Universe. If we go to smaller and smaller times since the Big Bang, the green circle shrinks to a point, but the 78 billion light year box is always full, and it is always an infinitesimal fraction of the infinite Universe. Note that the black dots represent galaxies, and the galaxies do not expand even though the separation between galaxies grows with time." At age of 1Gyr all the galaxies were quite close to each other, the density is very high and it looks as homogenous and isotropic Universe. Therefore, the transient from 1Gyr to 13.0 Gyr is quite simple and logical. However, let's try to understand the process from 1Yr to 1Gyr (or even from 1sec to 1Gyr). Please look at the following diagram picture: http://www.wisegeek.org/what-happened-after-the-big-bang.htm#expanding-universe-after-big-bang At 1Yr there are no galaxies. The whole Observable mass is concentrated at the size of the Milky way. Lets call it Early observble Universe. As there are galaxies all over the Universe, can we assume that there was many (or infinite) spots (at the size of our milky way) which represents other early observable universes? If that is correct than I have the following questions: 1. Could it be that there was not just one Big bang but an infinite no. of bangs? (each one set a new observabale Universe)? 2. If so, how could it be that all those bangs started exactly at the same moment? 3. Why they do not collide with each other? 4. How could it be that with so many bangs the Universe had been transformed to its current homogenous and isotropic shape?

https://medium.com/starts-with-a-bang/how-is-the-universe-bigger-than-its-age-7a95cd59c605

Thanks Great answer. That is a key issue. Let me use an example of a car in a motor way. At any given time we can measure its current speed. But that doesn't give any confidence that this speed was constant forever. In the same token, as all the above parameters might change over time, than by definition (based on the formula) we might get significant change in the calculated age. Different age means - different size of Universe. Hence, if I understand it correctly, our Universe might be bigger or smaller than our current expectation.

Thanks Correlation between the Universe age and its size: Let's look at the following diagram: At age of one second - the size of the Universe is just over one light year. At age of one year - The size of the Universe is less than the size of the Milky Way Galaxy. At age of 13.8 BL (Today) - What is the size of the Universe? (Is it 92 BLY)? In the same token, what is the expected maximal size of the Universe with regards to its age (at one second, one Year and today)? Could it be (for example) that at age of only one year the size of the Universe is over than 100 times the size of the Milky Way or even infinity?

What is the meaning of: "The rest of the universe beyond the observable universe". Let's start by understanding the meaning of: "observable universe" https://en.wikipedia.org/wiki/Observable_universe "The observable universe is a spherical region of the Universe comprising all matter that can be observed from Earth at the present time, because electromagnetic radiation from these objects have had time to reach Earth since the beginning of the cosmological expansion." The word observable used in this sense does not refer to the capability of modern technology to detect light or other information from an object, or whether there is anything to be detected. It refers to the physical limit created by the speed of light itself. Because no signals can travel faster than light, any object further away from us than light could travel in the age of the universe(estimated as of 2015 around 13.799±0.021 billion years[5]) simply cannot be detected, as they have not reached us yet. In practice, the limit on observation is not 13.799 billion light-years for two reasons.[10] The first reason is that space itself is expanding, so we can actually detect light from objects that were once close, but are now up to around 45.7 billion light years away (rather than up to 13.799 billion light years away as might be expected).[10] The second reason is that before the recombination epoch, about 378,000 years after the Big Bang,[citation needed] the Universe was filled with a plasma that was opaque to light, and photons were quickly re-absorbed by other particles, so we cannot see objects from before that time using light or any other electromagnetic radiation. (Gravitational waves and neutrino background would have been unaffected by this, and may be detectable from earlier times.)" Hence, if I understand it correctly - "observable universe" means the maximal predicted size of the Universe based on its age, space expansion... as estimated by BBT and the speed of light. We can't really see this Spherical region. We just know that based on the above data by the BBT and the speed light limit, that region is the maximal size of the Universe. Therefore, it seems to me that as long as the real Universe is in the equal or smaller than the observable universe, it meets the prediction by the BBT. So how could it be that the rest of the Universe could be bigger than the maximal predicted spherical region of the Universe (45.7 BLY)?

O.K. Let me ask the following: Based on the BBT we can give an explanation for the Observable Universe - That is clear! We can justify how a Universe with a radius of 42 BLY had been evolved in time frame of 13.8. However, it was stated that the real universe is bigger than the observable Universe. Some claim that it might be Infinite some might claim that it isn't - However, at least it is very big comparing our tiny observable Universe. The results from the WMAP show the universe/spacetime to be very nearly flat, at least within very small error bars. A flat universe denotes an infinite universe. Of course it is also possible that an even more accurate methodology may see that flatness as simply the small part of a much larger curvature. With regards to the BBT It is stated: Because it is still the best explanation for all the evidence. How could it be the best explanation if it can't give an explanation for the real size of our Universe? So even if the BBT gives perfect explanation to the Observable Universe, how can we ignore the rest of the Universe? But again - the time frame of 13.8 Billion years gives an explanation for a maximal universe size of 42 BLY. what about the rest? It doesn't. It describes the evolution of spacetime from 10-43 seconds post t, to what we are able to observe today. If the Universe is infinite, it would always have had to be infinite, and going back in time would just shorten the distances between any two points, up to around t+10-43 seconds. If the Universe is infinite, it would always have had to be infinite Hence do you mean that if the Universe is infinite, it was there infinite time before the BB (So, it age is intinite)? In the same token, If the Universe is bigger than the Observable Universe could it be that it was there before the BB? If the Universe was there before the BB, while the BBT doesn't cover its existence, than could it be that there is error in the BBT? I'm quite confused with that.

Yes, I agree that the Universe is not a star. I also agree that the density and the temp is much lower than an average star. But, why a special/unique star can't be in low density and low temp? Is there any limitation for star density or temp? However, if you don't like to call it star - then let's keep it under the name - Universe. Yes, the radiation from star is not black body. But that was not my intention. What about the radiation inside the star or in the photosphere? It is stated that it has a black body radiation. https://en.wikipedia.org/wiki/Black_body#/media/File:Idealized_photosphere.png "An idealized view of the cross-section of a star. The photosphere contains photons of light nearly in thermal equilibrium, and some escape into space as near-black-body radiation". But why? The answer is - thermal equilibrium: "The photosphere contains photons of light nearly in thermal equilibrium". Therefore, let me ask the following questions: 1. do you agree that if the Universe is in thermal equilibrium its radiation should be black body (or near black body)? 2. If so, what is needed for the Universe to be in thermal equilibrium? Do you agree that there is only one solution for that - an Infinite Universe?

Except it isn't. It is a collection of stars and galaxies separated by largely empty space Don't you think that on large scale the Universe is homogenous? It is stated that: https://en.wikipedia.org/wiki/Friedmann_equations "The Friedmann equations start with the simplifying assumption that the universe is spatially homogeneous and isotropic, i.e. the cosmological principle; empirically, this is justified on scales larger than ~100 Mpc." https://en.wikipedia.org/wiki/Cosmological_principle "Although the universe is inhomogeneous at smaller scales, it is statistically homogeneous on scales larger than 250 million light years. The cosmic microwave background is isotropic, that is to say that its intensity is about the same whichever direction we look at.[8]" If the Universe is Infinite, than could it be that a scale of 250ML years is like one grain of sand on Earth? Hence, don't you agree that on large scale the collections of stars galaxies and space are homogenous? In this case, why we can't consider it as an Infinite star with a density of: https://hypertextbook.com/facts/2000/ChristinaCheng.shtml "The critical density of matter in the universe that separates the two possibilities can be calculated from Einstein's theory. It is now approximately 10−30 grams per cubic centimetre. Small though this value maybe, it separates two entirely different futures for the universe" and a temp of 2.7K?

1. I claim that CMB in an Infinity Universe should carry a black body spectrum. https://en.wikipedia.org/wiki/Cosmic_microwave_background The CMB has a thermal black body spectrum at a temperature of 2.72548±0.00057 K. 2. We have to look at the Infinite Universe as an Infinite star. The radiation in an Infinite star does not leave the star. Therefore, as long as the radiation is located inside the Infinite star, it is in thermal equilibrium. Hence, we get it as a black body radiation. If the Universe was not infinite, than the radiation had to leave the Universe. In this case, once the radiation leaves or is decoupled it is no longer in equilibrium and it has no black body spectrum. That proves that the universe is Infinite

It seems to me that you are missing the point. The Internal radiation inside a star (or inside the photosphere) is a Black body radiation. Therefore, as small portion of this radiation is ejected out - it carries the black body signature. If the Inside radiation was not a black body then by definition it can't be a black body radiation as it goes out.

https://en.wikipedia.org/wiki/Black_body A star or planet often is modeled as a black body, and electromagnetic radiation emitted from these bodies as black-body radiation. https://en.wikipedia.org/wiki/Black_body#/media/File:Idealized_photosphere.png An idealized view of the cross-section of a star. The photosphere contains photons of light nearly in thermal equilibrium, and some escape into space as near-black-body radiation. Not Infinite number of stars but one Infinite star.

What is a Black Body ? A black body is an ideal body which allows the whole of the incident radiation to pass into itself ( without reflecting the energy ) and absorbs within itself this whole incident radiation (without passing on the energy). 1. So could it be that an infinite object as an infinite Universe meets this expression? 2. An Infinite Universe could also be considered to an infinite Star. We know that a star has an internal black body radiation. So, if a star has an internal black body radiation, why an infinite star (as an infinite Universe) couldn't have that kind of radiation? If that is correct, than the black body radiation of Universe proves that our Universe must be infinite L