Question: I have read that the diameter of the universe is 96 billion light years. How can that be if the universe is a mere 14 billion years old? Am I to conclude that the 96 billion figure is some extrapolation based on rapid inflation? – Carlton
Answer: One of my physicist colleagues, Frank Heile from Stanford University, has provided an excellent answer to this question. First of all, the 13.8 billion light years is derived from the radius of a sphere of the Cosmic Microwave Background (CMB) radiation that is being observed by the Wilkinson Microwave Anisotropy Probe (WMAP) and Planck satellites. These satellites have mapped the structures which are precursors to galaxies and clusters of galaxies. Second, the 93 billion light year diameter estimate refers to the “observable” universe.
Now, if we waited another 46.5 – 13.8 = 32.7 billion years, we should actually be able to see the light emitted right now from those superclusters of galaxies which formed from the CMB structures. The light is already on its way towards us but it will take a while to reach us since it will have to come from a sphere with a diameter of 93 billion light years. This is the explanation for the difference; the “observable” universe is larger than we can see it today.
This is only, at best, a theoretical estimate of the diameter of the universe, though. We now know that due to dark energy the expansion of the universe is accelerating. This acceleration will not allow us to see those superclusters which are now 46.5 billion light years from us. In fact, if we wait the requisite 32.7 billion years those superclusters will be receding from us at a rate that is greater than the speed of light. We just will not be able to observe those galaxies and clusters of galaxies which have formed at the edge of the universe.
Question: What does the structure of the universe look like at the largest scales?
- Galaxy cluster are distributed evenly throughout space with no large gaps
- There are many more galaxies and clusters in some directions (up and down the milky way’s disk) and very few galaxies in other direction
- Linear or wall like distributions of galaxies, clusters, and superclusters surrounding relatively empty regions- like soap bubbles
- Galaxies and cluster are very thiny spread out in the near distance, and are more closely packed at greater distances from the milky way
Answer: I think that option 3 comes closest to the actual distribution of galaxies in the universe. The large-scale structure of the Universe is made up of filaments and voids. When we look closely at the filaments, we find that they can be broken down into superclusters, clusters, galaxy groups, and finally into galaxies.
Question: Is it possible that the big bang occurred in a pre-existing universe? if not, how do we know? – Gary
Answer: I think that the best evidence to support the fact that the Big Bang happened in this universe is the fact that we see evidence for its existence in our universe. There really isn’t any reason to invoke the existence of another universe to explain the Big Bang.
Question: Isn’t it possible that the answer to the increasing speed of the expansion of the Universe is that it is being pulled apart not being pushed apart? If the “unknown” Universe was trillions of light years of dark energy and when the “singularity” appeared, it would have exploded, for lack of a better term, inflation would have occurred, then as gravity was created, the expansion would have slowed down but as the years have gone by the power of all that dark energy, as thin as it is, will eventually overcome the gravity contained in the “known” Universe and pull it into oblivion. – Philip
Answer: To suggest that the accelerating expansion of the universe is caused by a “pulling” force rather than a “pushing” force would require identifying the source of the “pulling”. Dark energy is theorized to be a component of the known universe that we had not originally appreciated. If one wants to incorporate an external force, then one needs to identify from where this force came, which is the difficult part.
Question: It is a challenging research topics to search how supermassive black holes formed at the early epoch. I am very much interested to do my future research on this topic. Could how please tell me what can be possible solution for this problem? How can SMBH formed at early epoch? – Anirban
Answer: The discovery of a supermassive black hole (SMBH) in a quasar (a special kind of galaxy) which is at a redshift which places it at an age of only about 900 million years after the Big Bang certainly pushes the theory of the formation of SMBHs. One of the most popular theoretical scenarios associates the first massive black holes with the remnants of the first generation of stars in a galaxy. I believe, though, that the discovery of this very young SMBH means that the formation of black holes must happen over a much shorter timescale than previous believed.
Question: If the universe is expanding and all galaxies are moving away from each other, how is it possible that the Andromeda and milky way galaxies are on a collision course? – Johnny
Answer: It is correct that on the largest scales that the universe is expanding such that all galaxies are moving away from each other. On smaller scales, though, there are so-called “peculiar motions” of galaxies, where one galaxy is found to be moving toward another galaxy due to local gravitational effects in the vicinity of the two galaxies.
Question: Hi! I am from Salt Lake City Utah. I’m in the sixth grade and in middle school. Middle school is really amazing and I love it. But what I love about it the most is my science teacher. His name is Mr. Krause and he is the best. he is smart funny and explains stuff in the best way! Right now we are almost done with astronomy. We started talking about the universe and I asked him this question and got a good answer but I thought I could ask you and get an even better answer? Here it is: Could we be looking at the size of the universe the wrong way? Could the universe just be one HUGE galaxy and there are multiple universes just like there are galaxies? Perhaps one day one universe will collide with another just like galaxies in our own universe.
Thanks for reading my comment! Astronomy has always interested me along with many other things about our world and its history like the past cultures. Thanks again and I hope you understand what I am trying to say. – Kailey
Answer: That is really great that you have such an amazing science teacher! You should be sure to tell him how much you enjoy his teaching. As for your question about how we view the universe, let me just say that any description of the structure of the universe has always to be based on measurements. In fact, this rule that any explanation of anything has to be based on fact applies to everything in science. Now, since we observe stars and galaxies in our single universe, and we believe we have a pretty good understanding of how they interact and evolve, we feel confident that our observations are described very well by a single universe. To turn that around, we can definitely say that we have no evidence for there being any additional universes other than our own. That said, it is still possible that there are multiple universes, the evidence for which we just have not found yet. This is a hypothetical scenario, though, that is not based on any measurements we have made.
I do hope that you continue to enjoy your science class Kailey and that Mr. Krause enjoys teaching science as much as you enjoy learning it.
Question: I am not able to understand one thing, when we say we saw a star exploded billions of light years away, does it mean it exploded billions of light years ago but the light reached to you just now. Aren’t we studying the phenomena which has happened billions of light years ago. Is it possible that another big bang has already happened, just the explosion light/energy has not reached to us yet? – Dipanshu
Answer: When we say that we have seen a star explode that is billions of light years ago, it means that it exploded billions of years ago since that light from that stellar explosion had to travel billions of light years to get to us. Note, though, that a stellar explosion is not the same as the big bang, in that the big bang expansion started everywhere at once, and was not characterized by an explosion at a single point.
Question: Some years ago I read an article that said (if I recall correctly) that there were quasars that seemed to be associated with galaxies (maybe in the center), but the quasar’s much larger red shifts implied that their distance was far more than the associated galaxies’ distances. Has this ever been resolved? – Bill
Answer: The research that you are referring to was done mainly by two astronomers, Halton Arp and Geoffrey Burbidge. They proposed, based on observations of seemingly associated nearby galaxies and purportedly distant quasars, that quasars were simply ejected matter from these galaxies. In fact, once large surveys of galaxies (such as the Sloan Digital Sky Survey), became available it was possible to better test this apparent correlation. In summary, Arp and Burbidge were wrong, their assertion due in fact to what astronomers call a “selection effect”. If you are interested in more details on this now historical discussion see the Galactic Interactions blog post on the subject.
Question: We know that stars and galaxies we see are just fossil light as they were millions or billions of years ago. Is it possible to extrapolate the changes that we see today in those galaxies to determine their current state? – Vinod
Answer: In a way, yes. Since, as you point out, we see what amounts to the “fossil light” from stars and galaxies in the universe, we can piece-together how things evolve with time by sampling various times within this fossil record to study the evolution of these stars and galaxies. Note also that the timescales for the evolution of objects in the universe are, with few exceptions, much longer than a human lifetime, or even the total historical record of scientific measurements. This means that astronomers must study the evolution of just about every object in the universe by sampling its evolutionary state at different times in the cosmological record.