Shop Windows to the Universe

Ready, Set, SCIENCE!, by the National Research Council, focuses on K-8 science classsrooms. Check out the other publications in our online store, as well as classroom materials.

Quickie Questions - Astronomy - Universe

Date Answered Questioner (age, location) Question Answer
March 6, 2011Gavin(Memphis TN)How big is space?There are two parts to the answer to the question "How big is space?". Part one is to consider how old are the most distant objects we can see, which is about 14 billion years. Part two is to consider that during that time, the universe was growing. After a little mathematics you calculate a size of 47 billion light years.
February 22, 2011George(New York)All substances in the universe moving away from each other.
But Is there no end to it?
Could you put your answer Astronomy Anomalies ?
See The Future of the Universe. If the motion of substances away from each other is fast enough, it will overcome gravity and never end (like a rocket exceeding escape velocity from the Earth). Otherwise, in the far distant future gravity will overcome motion and everything will return to one small volume again, a Big Crunch to reverse the Big Bang.
February 21, 2011George(New York)What is the difference between dark matter and dark energy?Matter and energy are equivalent in the sense that either can be converted into the other, such that the total matter plus energy in the universe, M, never changes. "Dark energy" is a hypothetical energy whose existence would help explain the observed accelerating expansion of the universe. Dark energy is about 73% of M, but only 1 gram in a cube 50,000 kilometers wide. "Dark matter" is also inferred to exist to explain cosmological observations, but is about 23% of M, and more variable in density than is dark energy. Both things are called "dark" because only gravity can "see" them, not light or any other forces. [Sources: Wikipedia and recalled lectures.]
April 23, 2010Rahul (India)why are galaxies moving from each otherThe most accepted theory about the origin of the universe is the Big Bang. This explains why the galaxies move away from each other as a result of the Expanding Universe.
February 22, 2010david (aberta canada)I'm a little confused. I've seen a program on discovery. Showing how they look at the universe, they look at light that reaches from millions of light years away. Which shows the past. How can they look at the Big Bang, aren't we part of the Big Bang. When it happened. And we are still moving away from that original spot.Cosmology is the the branch of astrophysics that studies the origin, evolution and structure of the universe. Its history is closely linked to the development of new ideas about the origin of the universe. While we can't see the Big Bang, there are related discoveries, like the The Cosmic Microwave Background Radiation that supports the Big Bang theory. All the visible universe seems to be expanding or moving away from a common point. More information on our web page Hubble Flow: The Expanding Universe , and the links therein.
February 10, 2010María (Sevilla, España)Vivo en Sevilla, mi madre es tu amiga y tengo una duda:
Por qué el espacio es negro?
Tu pregunta, aunque parece sencilla, ha sido formulada por siglos sin respuesta. La lógica indica que si el universo está lleno de estrellas, ¿Por qué la luz proveniente de ellas no mantiene el cielo completamente iluminado? Éste sería el caso si el universo fuera infinitamente grande e infinitamente viejo. Bajo estas condiciones verías en cualquier dirección que mires, una estrella. Pero por experiencia propia sabemos que no ocurre así, y esta contradicción es conocida como la Paradoja de Olbers. Aunque se han propuesto muchas explicaciones, la más aceptada actualmente es que el universo no es infinitamente viejo, tiene unos 15 mil millones de años. Esto significa que no podemos ver objetos que estén más allá de la distancia que luz recorre en ese tiempo. La luz de las estrellas que están más lejos de esa distancia no nos ha alcanzado, y no contribuyen a la iluminación del cielo. Para terminar una observación interesante, si sumamos todas las radiaciones de todos los objetos visibles, el color resultante del universo NO es negro. El artículo The Cosmic Spectrum and the Color of the Universe ofrece mucha información sobre el tema. ¡Pídele a tu mama que te ayude a traducirlo!
January 25, 2010kate (france)which statement is true about the creation or begining of the universMost scientists currently accept the theory of the Big Bang as the most likely origin of the universe.
January 18, 2010Steve (Virginia, USA)If our universe is supposedly in an expansion phase as a result of the theorized "Big Bang", then initially there was a "Big Crunch" at some point that all matter and energy existed in one point. Did time exist during this event? If this event was considered just that "an event" then did time exist before the universe began? Even before the "monobloc" phase? Or does time begin to exist when an event is "observed"?The "Big Crunch" and the "Eternal Universe" are different options offered by Cosmologists for the future of the Universe. This is a still an open topic. The following articles offer a good discussion on these issues, http://skyserver.sdss.org/dr1/en/astro/universe/universe.asp, http://csep10.phys.utk.edu/astr162/lect/cosmology/expansion.html, and http://archive.ncsa.uiuc.edu/Cyberia/Cosmos/ExpandUni.html.
January 12, 2010natasia (north carolina)what evidence shows that the universe is expanding?It was Edwin Hubble, during the 1920's, who first provided evidence that we live in an expanding Universe. Hubble's observations showed that the greater the distance to a galaxy, the greater the redshift in its spectral lines. These measurements strongly indicated that galaxies appear to be moving away from us with speeds proportional to their distance.
January 11, 2010 If gravity were to disappear completely from the Universe would the Universe reach its maximum entropy as a result of that?This is a question better answered by a expert in Cosmology, but here are my two cents: I don't believe that this hypothetical condition (an Universe with no gravity) will imply a maximum entropy condition. There is still the kinetic energy of the system available for work.
October 16, 2009Keerthi (Karnataka)How was universe created?The most widely accepted theory among scientsts is The Big Bang Theory. Please, visit our web page The History of the Universe for more information.
October 13, 2009Phil (ct, usa)How do scientists know the universe is expanding faster do to dark matter/energy or rather from the intense explosion from the big bang ( in an explosion matter accelerates to a point until an outside force -air resistance, gravity, etc. affects it but continues to accelerate until that point. How do we know we are not still in that acceleration stage?This is a still open topic of discussion. The following articles offer a good discussion on this topic, http://skyserver.sdss.org/dr1/en/astro/universe/universe.asp http://csep10.phys.utk.edu/astr162/lect/cosmology/expansion.html http://archive.ncsa.uiuc.edu/Cyberia/Cosmos/ExpandUni.html
October 6, 2009Rishabh (India)How entropy will be created if the universe keeps on expanding?This is still an open question in science. For a good discussion on the subject visit this page.
September 17, 2009mariam (UK)We always see the images of a unviverse expanding in a cone shape (erupting from a big bang at point1) why isn't it depicted as a sphere, if an explosion occurs at point1 then the expansion should be uniform in all directions spherically no?Yes, you are right, the Universe expands in all directions. See our representation of the expanding Universe here.
August 24, 2009Rebekah (São Paulo BRAZIL)I would like to know about the "beggining of the universe" I have to do a work about it.There are several theories about the beginning of the universe, the most widely accepted is the Big Bang. Our web page The History of the Universe and the links therein discuss this theory.
August 21, 2009SRISHYAM (India)Is there anything called 'alternate' universe?Yes, it is a technique used in literature to open new possibilities for the writer ad readers. An alternative universe fan fiction is a form of fan fiction in which canonical facts of setting or characterization in the universe being written about are deliberately changed. More information here. Now, regarding the possible existence of others universes, it is better to read this article.
August 18, 2009tyson (australia)i know of the big bang theory but cant help thinking of other way the universe could end!

is there another way th universe could end
The two main theories for the future of the universe are explained in our web pages The Big Crunch and An Eternal Universe.
July 24, 2009Miguel (Puerto Rico)If the nebulae are regions that form stars from the remaining materials of dead stars, why the nebulae will not supposed to form new stars in the cosmological decades from 15 to 37 (Degenerate era)?When stellar evolution, the current Era, comes to an end, we enter the Degenerate Era, where most ordinary stars will have finished nucleosynthesis as stellar bodies. Lots of information about this topic can be found here.
March 23, 2009Rich You state that the Universe is expanding. What is it expanding into?For a more in depth discussion on this topic see the following links: http://skyserver.sdss.org/dr1/en/astro/universe/universe.asp http://csep10.phys.utk.edu/astr162/lect/cosmology/expansion.html http://archive.ncsa.uiuc.edu/Cyberia/Cosmos/ExpandUni.html
March 10, 2009elena (MI/usa)is the universe flat or round or a bungi cord type of univerise?The answer to your question lies in the field of Cosmology. This short although interesting article will give you some answers.
January 29, 2009akshata (india)does the universe expands uniformly from everywhere?and if gravity slow downs the expansion rate then the universe will somehow end?To your first question the answer is yes, now, it would be better to visit our web pages The Big Crunch and An Eternal Universe to answer your second question regarding the end of the universe.
November 7, 2008VinayWhat is the future of the universe?What is the Future of the Universe? We may still be far from answering the question definitively, but we are at least able to predict certain possiblities. In our current view of the Universe there are 2 possible futures. One possiblity is that the Universe will come to an end in the opposite of a Big Bang called The Big Crunch, the other possibility is that we live in an Eternal Universe that will never come to end.
September 26, 2008MONIKA (NEW DELHI, INDIA)WHAT IS IN THE CENTER OF THE UNIVERSE? IF THERE IS A BLACK HOLE, THEN OUR GALAXY MUST BE ATTRACTED BY ITS GRAVITATIONAL FORCE, IS THAT RIGHT? IF IT IS THEN UNIVERSE MUST NOT EXPAND. IF THERE IS NO BLACK HOLE THEN WHAT IS THERE?We don't know what where is the center of the universe. This has been a permanent question hovering in the human mind forever. A great discussion on this topic can be found here. On the other hand, the graviational force is inversely proportional to the square of the distance, therefore the gravitational force is close to zero for great distances. Furthermore, other objects gravitational fields are closer, and more intense, like our Sun's and galaxy's.
September 22, 2008gurdish (india)Is this possible that many other universe like ours are present or many other big bangs occured?Yes, it is possible, but we don't know yet. The Big Bang theory have two options, one of them, known as the Big Crunch states that if there is enough matter in the Universe eventually gravitaional forces will stop its expansion. When this happens gravity will cause the universe to reverse its direction and begin to collapse under its own weight into a super dense state and possibly even collapse into an unimaginably massive black hole. Some theorize that the Universe could collapse into the same state that it began as and then blow up in another Big Bang. In this way the Universe would last forever but would continually go through these phases of expansion and contraction (Big Bang and Big Crunch).
September 9, 2008jimmy (U.S.A.)how big is our universeThe NASA website How Big is the Universe offers a nice discussion about your question.
July 1, 2008Aldrin (United Kingdom)If the universe had a beginning what was going on before that?The answer to your question is not straighforward, it involves a lenghty explanation, like this one.
May 13, 2008Sarah (England)How old is the universe?The age of the universe is the time elapsed between the Big Bang and the present day. Current observations suggest that this is about 13.73 billion years, with an uncertainty of about 120 million years. Adapted from Ned Wright's Cosmology Tutorial.
April 10, 2008Tameka (irvine,KY)what was the early universe like?This is a question that escapes the reaches of this section, but you can find a good deal of information on this topic here.
March 10, 2008LiamIs the universe flat or round?Besides many scientific efforts, this is still an open question. Different theories will offer different answers, but none is considered final (yet).
October 18, 2007(Australia NSW)I have heard that after the sun will die it will then eat all of the inner planets. My question is like there was a start to the universe with the theory the "Big Bang" will there be an end to the universe or will it continue to just keep going on?In our current view of the Universe there are 2 possible futures. One possiblity is that the Universe will come to an end in the opposite of a Big Bang called The Big Crunch. The other possibility is that we live in an Eternal Universe that will never come to end. Please, visite the two links to obtain more information on this topic.
January 16, 2007seth (usa)what is the big bangThe Big Bang is the prevailing scientific theory about the origin of the universe. According to the theory, the universe was created (between 10 and 20 billion years ago) from a cosmic explosion that threw matter in all directions.
February 25, 2003Jake (Minnesota, USA)If the light from the 'Big bang' (the source of everything) is just now arriving, how did we (and everything we observe) get here before it?Space in our Universe is actually "curved", not "flat". Imagine you lived in a two-dimensional Universe instead of our three-dimensional Universe. If your 2-D Universe was flat (like a giant tabletop) and you shined a light in one direction, it would go on forever. Now pretend your 2-D Universe was curved (like the surface of a very large ball). If you shine a light in one direction, the light would eventually go all the way around the ball and hit you in the back of the head. Our 3-D Universe is actually curved! Einstein predicted this in his theory of relativity, and was proven correct when astronomers measured light curving as it went past the Sun. Light from the Big Bang has made several laps around our Universe by now.
November 19, 2002Denis (India)Explain Olber's paradox.Olber's Paradox is a question that asks "Why isn't the night sky as bright as the sun?" If the Universe is thought to be infinite, with infinite stars, then everywhere we look we should see stars (even very far away), and these stars should contribute to the night sky being as bright as the sun. The best explanation (and answer) I found are on this page.

July 14, 1999Bhupendra (India)What is the fate of the universe? Is it going to expand indefinitely as Dr. Stephan Hawkings says, or start contracting again?Nobody knows for sure with our current knowledge what the ultimate fate of our Universe will be. One of the key factors is how much dark matter actually exists in the Universe. Stephen Hawkings is a brilliant man, but he has been wrong before. His field is so highly theoretical that little can be known for certain, and his opinion on the fate of the Universe is just that, an opinion.
June 16, 1999Sergio (Oregon)How many galaxies are in the universe?
How many stars are in each galaxy?
There are over 100 billion galaxies in the visible universe. The number of stars in each galaxy varies widely, but each galaxy probably has a couple billion stars on average. Talk about alot of stars!
June 11, 1999anonymous Approximately how old is the universe?While scientist cannot agree exactly, recent research has found an accurate approximation of the Hubble Constant. The Hubble Constant can predict the universe's age because it deals with how fast the universe is expanding. Read about it here.
May 25, 1999Jed (Nebraska, USA)Where does the word Universe come from?Universe is made from joining the words uni and verse. Uni means "one". Verse comes from the Latin word versus, which means "to turn". So, the Universe means "one turning". That means that the Universe is one whole thing turning! Pretty neat, huh?
January 29, 1999MatthewHas anyone developed a map of the universe? On Star Trek they talk about things like alpha quadrant or delta quadrant etcetera. I'm curious if that has any basis in reality and if so what the map for that looks like.No. There are many things to learn about and discover in our universe. To date, only a tiny fraction has been mapped. In our own solar system, however, we know generally the major components, and have a pretty good idea of most of their positions.
September 8, 1998Duleep_Bear (Australia)What is the age of the Universe?There is much debate over the current age of the universe among astrophysicists. But everyone agrees that it is somewhere between 10 and 20 billion years old.
June 3, 1998Yee (Malaysia)Will the universe expand forever? Why?The future of the universe is uncertain. There are two possibilities at this point; either the universe will end in the Big Crunch or it will expand forever. Right now, we just don't know which one will happen!
April 8, 1998Ruben (California, U.S.A.) When the universe expands does space expand or matter is created?Space is expanding with the Universe. But all the matter in the Universe was created during the Big Bang; most astronomers believe that no new matter has been created since then.
April 8, 1998Ruben (California, U.S.A.) What is space? What is it made of?Often when we talk about space we mean the region between stars, planets, galaxies...everything in the Universe. What is space? Better ask what it isn't! We distinguish space from the objects in it by the lack of matter. In empty space, there may be only a few atoms in a volume as large as your head. Even a gaseous nebula is more dense than that.
March 24, 1998Simon (Australia) If everything in the universe is accelerating away from us in every direction, are we at the center of the universe? If not where did the 'big bang' happen?We are not at the center of the universe. Everything is moving away from us because the universe is expanding. It is kind of like dropping a stone into a pond. The points on the circle are all moving away from each other, even though none of them i s at the center.
As for where the Big Bang took place, the best description is that it occurred in every single point of space in the universe. It had no single starting point. This is because it did not occur in space, it created space.
March 3, 1998Ronnie (Texas, USA) In any explosion, the force exits in a sphereical shape. From the 'Big Bang' theory, is the universe in a spherical shape, everything still going away form the center?The shape of the Universe actually depends upon its density. If the density exceeds the "critical density", then the Universe would indeed be shaped like a sphere. However, if the density is less than the critical density, the Universe is curved like a saddle. And, if the density of the Universe exactly equals the critical density, the Universe is flat like a sheet of paper. Astronomers still do not know the exact density of the Universe, but the most widely accepted theory holds that the density is very close to critical density, so the Universe is probably closest to the flat model.
February 18, 1998Sam (Finland) Is it true that the universe is expanding all the time and if it is so is there any limit in this expansion?In the 1920s, Edwin Hubble, for whom the Hubble Space Telescope is named, discovered that all galaxies appear to be moving away from our galaxy. The Big Bang theory, which currently best explains this and many other observations, predicts that the universe is expanding. However, it is not yet known whether this expansion will continue forever, or whether the gravity of the universe will eventually stop and reverse the expansion, leading to the 'Big Crunch'. This depends on the mass density of the universe, a very hot topic of debate among astronomers.
January 29, 1998Brianna (Alabama, USA)Do you really think the universe will end in 'the big crunch?' I know you said it is just a possiblity, but why?If the universe has a certain amount of matter in it (planets, stars, gas, etc.)...it is 'heavy' enough so that its own gravity would pull it together so that the universe would end in 'the big crunch'.
Recent discoveries (just last month) point to the fact that the 'big crunch' will probably not occur. The universe will just keep expanding forever! So no worries!
January 29, 1998Steve (Kansas, USA)Do you think it is possible that our galaxy and even the known universe are nothing but an infinitely small piece of something much, much more grand, something like an atom is but a small piece of cell and the cell is but a small piece of a larger organism and so on etc. Couldn't our universe be nothing but a cell of something much bigger? They say that the universe is as infinitely small as it is infinitely big!I guess it is a possibility...the only thing is, the universe is everything that exists in space and time. So, unlike a three dimensional atom which is part of a three dimensional cell which is part of a three dimensional human, this "something bigger" would have to be of a completely different set of dimensions, meaning we could have no physical contact with it. So, unless we figure out how to get into other dimensions, we will just have to use our imaginations.
January 29, 1998---Is there another universe?If there is another universe, we will never be able to have any physical contact with it. Our universe is everything that exist in space and time, so any other universe would have to exist in a completely different set of dimensions.
January 20, 1998Eric (Virginia, USA)What is the geometric relationship between the Great Pyramids in Egypt and our universe?Apparently, some of the pyramids were laid out in a manner corresponding to constellations such as Orion's belt. Others seem to match stars important to particular Pharaohs or dynasties.
January 16, 1998James (Oregon, USA)If the universe started as a point, what was outside that point?Nothing like the space-time we know now existed before the Big Bang. At that moment, in less than a quadrillionth of a second, enough energy to make all the material in the entire universe came into being, and was converted into atomic particles. But we don't know how or why all this worked, and most of us have trouble imagining such a great nothingness!
January 16, 1998David (Norfolk, England)What is (in terms of a range) the current estimated weight of the universe including dark matter?One of the key issues of astronomy concerns just this question - how much matter is really out there? Astronomers usually talk about the density of the universe not the weight of the universe. Astronomers have defined a "critical density" that ultimately determines the fate of the universe. If the density of the universe is less than the "critical density" then the universe will expand forever. If the density of the universe is greater than the "critical density" then then universe will end in the Big Crunch. Although there is still a lot of debate over the actual density of the universe (because of debates over things like dark matter), current findings show that the actual density of the universe is less than the "critical density" so the universe is likely to expand forever!
December 2, 1997Bobby (Quebec, Canada)How old is the universe?Although there remains considerable dispute over its precise age, the age of the universe is often cited as 15 billion years old. However, nearly everyone accepts that it lies somewhere in the range of 10 to 20 billion years old. Visit our pages on the history of the universe or cosmology to learn more about how the universe was formed.

Windows to the Universe Community

News

Opportunities


Windows to the Universe, a project of the National Earth Science Teachers Association, is sponsored in part is sponsored in part through grants from federal agencies (NASA and NOAA), and partnerships with affiliated organizations, including the American Geophysical Union, the Howard Hughes Medical Institute, the Earth System Information Partnership, the American Meteorological Society, the National Center for Science Education, and TERC. The American Geophysical Union and the American Geosciences Institute are Windows to the Universe Founding Partners. NESTA welcomes new Institutional Affiliates in support of our ongoing programs, as well as collaborations on new projects. Contact NESTA for more information. NASA ESIP NCSE HHMI AGU AGI AMS NOAA