Does the Universe have an edge?

I don't think anyone really knows. There are lots of ideas, though. If there has only been one Big Bang (which in itself seems unlikely to me), then the Universe has an average radius, approximately the age of the universe times the speed of light, ignoring the possibility of stuff that travels faster than the speed of light. Intergalactic space is thought to have an average density of something like 1 hydrogen atom per cubic meter [citation needed] although recent news from the big telescopes suggests that there are stars and planets also outside of galaxies. 1 atom/m^3 is pretty empty.  If the universe is alone, I suspect there is no way we will ever see its edge, as it is receding from us at or faster than the speed of light.

There are cosmologists who believe in all seriousness that our universe is expanding like a bubble in a foam of universes, in which case it is possible, I suspect, that we will some day detect the boundary, where it impinges on another universe. Does the edge slow down? Is there a shock wave? Please forgive me for being so Newtonian about this, but I can't imagine a foam of universes where all of them can expand indefinitely at or above the speed of light. Not, at least if they all share the same dimensions*. Then the question begs to be asked, does the foam have a boundary? What would be beyond that?

"It's turtles all the way down."

*What if our three familiar dimensions are actually dimensions #38576027184365756392,  #38576027184365756393, and #38576027184365756394, and other universes are also three dimensional but occupy other dimensions than our particular three of length, width, and height? (I am ignoring the 9, 11, 17 or whatever dimensions are required by string theory.)

Geology questions from a class after our Rocks! program.

How old is our meteorite?

The meteorite fell to earth from interplanetary space. That is, it probably originated inside our solar system. Because it is an iron-nickel meteorite it probably was part once of a larger body, a planet or other large object that was broken up in a collision with another large object.  Most of these collisions would have taken place in the first one or two billion years of our solar system which is about four and a half billion years old. That would make our meteorite probably about three billion years old, give or take a billion. That is really, really, really old, give or take a really.

How heavy are the rocks?

We have a big piece of petrified wood that doesn't travel on the van because it weighs about sixty pounds. Most of our rocks are a pound or two, the geodes and crystals weigh only fractions of a pound. We have tried to collect rocks that are big enough to be interesting to look at or are interesting enough that it doesn't matter if they are small.

How old is the pumice rock?

How old is the obsidian?

Both of these rocks were produced by explosions of the Valles Caldera volcano in the mountains behind Los Alamos and White Rock. I don't know if they were produced at the same time or during the same cycle of eruptions, but the last eruption was between one and two million years ago so that is as young as they can possibly be.

What is our newest rock?

Our newest rock is the concrete core sample which was cut out of a sidewalk sometime in the last twenty years. Concrete is a man-made rock, and I think this core was from a sidewalk somewhere up "on the hill" so it can't be more than fifty years old. There weren't sidewalks here more than about fifty years ago. Sometimes cores are cut to see what condition the concrete is in below the visible surface, other times they are cut to make a place to put up a new sign in the sidewalk.

The other young rocks are also man-made. Slag from the San Pedro Mine near Golden, NM is left over from a gold mining operation in the early part of the twentieth century, and we have one small piece of Trinitite in a plastic globe. The trinitite actually has a birthday, as it was formed when the sand below the first atomic explosion melted on July 6th, 1945.

How old is our oldest rock?

After the meteorite, which I discussed above, our oldest rock is a piece of quartzite from the Brazos Cliffs area near Tierra Amarilla, NM. The rock that forms these cliffs is the oldest surface rock in the state, and is about 1.7 billion years old. That is way before dinosaurs, in fact, it is possible a dinosaur may have tripped on our rock or turned it over looking for goodies to eat!

How many rocks do we have at the museum?

Please don't make me count them! In our rock museum, I think we probably use about forty rocks. We probably have three times that many either stored or in the sample bags. When we think of a rock that we would like to have for the program, we often go outdoors and look for it. It helps to know where to look.

How many pieces of pumice do we have?

We only travel with one piece of pumice, but you have to admit it is a good one! We have some small pieces, but pumice is so soft that when we take them around, they crunch against other rocks that are harder and they get ground into powder. So we usually leave them home.

What are our favorite and least favorite rocks?

I can only speak for myself, but all of the rocks in our program are favorites. My own personal least favorite rock is a boulder in a canyon near Taos that rolled one day when I stepped on it and I broke my leg.

My very best favorites are probably the meteorite and the dinosaur stomach rocks, but I am proud of collecting a very heavy piece of fossil pond scum that rarely visits classrooms because it is so heavy. Each of the rocks in the program has an interesting story, and most rocks you see around have good stories too. Sometimes it is hard to choose one rock story over another.

These are great questions, and as a teacher I can tell you that good questions are one of the nicest things you can give a teacher. Thanks for asking, and keep being good scientists!

How was the Earth formed?

How the earth formed is a long story, but I will try to make it shorter than it took for the Earth to form.

Shortly after the birth of our universe in the big bang, space was filled with energy and hydrogen atoms. (I am skipping over the question of dark matter and dark energy because I don't understand them.) Hydrogen atoms are the smallest and simplest atoms. As the Universe expanded, it cooled, and the hydrogen gas atoms formed clouds.

These clouds had gravity, and the gravity pulled the atoms closer and closer together. When atoms move apart, as in the expanding universe, they cool down. When they move together, as in these hydrogen clouds, they heat up. After a long time, they can get so close together and so hot that two hydrogen atoms smash together hard enough to fuse, or join together to make a helium atom. This releases energy, and more atoms fuse. This is the birth of a star, and it happened in places all over the universe.

Eventually the helium atoms start fusing with hydrogen atoms and with other helium atoms, and the star starts making heavier and bigger atoms like carbon, nitrogen and oxygen. This system works until our star starts making iron atoms, which are the limit for most stars. Iron is a very stable element, and difficult to fuse. Iron also poisons the star process, and when enough iron builds up, the star collapses. As the star falls in on itself, it again heats up, sometimes enough to blow itself to pieces.

This explosion, a supernova, has enough energy to create the rest of the elements that we know in nature, and blasts this stuff out all over the local part of space. This stuff is what Earth is made of. In time a new star was born, our sun. Earth is mostly iron and nickel metals, which are dense heavy materials, and at first it was like a huge pile of dust and rubble floating through space, orbiting the new star. Early in its life, Earth was smashed by something or several things huge, releasing enough energy to melt it. Iron and nickel sank towards the center, and the lighter, less dense elements floated to the surface. These materials today make up our atmosphere, oceans, earth's crust, and you and I.

How was the world made?

This is an interesting and deep question. The scientists who study this question are called cosmologists. Most cosmologists agree that our universe was born about twelve billion years ago in an event they call the big bang. While the science of the big bang is pretty well understood, it is difficult to explain, and very weird stuff. Some things that are important to know are that it resulted in a lot of energy and a lot of hydrogen gas that was spread out in lumps in the early expanding universe. It also apparently produced even more ‘dark matter’ and ‘dark energy,’ but no one knows what they are yet. Maybe you will be able to help us with that some day!

            After a few billion years, some of the lumps of hydrogen gas settled down and gravity pulled the hydrogen in the lumps closer and tighter together. This made the temperature rise; heating the gas so hot that nuclear fusion began. In nuclear fusion, atoms combine to make larger atoms. Fusion releases a lot of energy, raising the temperature of the gas balls, and creating new and heavier elements. These balls are what we call stars.

            The big bang made mostly hydrogen and I think a little bit of helium. These are the two lightest elements. Stars can cook all the elements up to elements as heavy as iron out of hydrogen and helium, but as the amount of iron increases, it slows down the action of the star. Eventually the star runs out of energy and collapses. The collapse of the star can set off another huge reaction that blows it to smithereens and creates even more elements, up to the weight of uranium. These are scattered throughout the space where the star had been.

            Our sun was born after this had already happened. It started as a lump of hydrogen, and condensed to become a star. The star had enough gravity to attract some of the remains of the earlier star, which condensed first into a ring or rings like those around Saturn, and then those condensed into the planets. Earth and all of its materials including you and me are the product of hydrogen from the big bang and everything else is from stardust. Earth condensed about four and a half billion years ago, and our sun will keep on being like a sun for Earth for at least another four and a half billion years.