Cosmology and our View of the World

Meeting Minutes 2 2/1/99

Procedural Information:

The session starts (at 6:10 PM - as it will in the future) with Prof. Eberhard Moebius (PEM) giving first practicalities about the upcoming sessions. After this current session and part of next week's session with an overview on Physical Cosmology, Prof. Paul Brockelman (PPB) will give the next two sessions on Spiritual Cosmology. Participants are encouraged to sign up for a topic on the list or choose another topic if they go for credit. Since we have many participants it is also possible to pair up with another person. The first student led session will be February 22: "What is reality?" by Melanie. Another session will be: "Mysticism & Science" by Marianne. PPB suggests a topic on: "Theories of Creation". For this topic it is recommended to read Stephen Hawking, Paul Davies, or also articles in the Astronomy Magazine. P.J. would like to do this topic. Two books are suggested: "The dancing Universe" and "The lost Paradigms". We also want to discuss certain articles we might find and they can be distributed.

Lecture and Discussion:

PEM starts his talk with a cartoon slide, explaining that a scientist is only talking about the observable universe. There are limitations by answering questions like: How did it evolve? Has it exist always? Will it exist forever? We have not a full answer, but a picture and questions. We see a picture from the last century: The universe as a room where one has the tendency to stick ones head out to discover another universe, another wall, look beyond that, and so on, and so on. - As a different analogy "The Gallery" picture from Escher shows us a loop: The observer looks at the observer. The universe is similar, seeing ourselves, our brain, the picture of the universe. As we research the universe, we cannot detach ourselves from it. Descartes, a French philosopher once suggested for all scientific work (known as the "Cartesian Cut"): The experimenter has to be detached from the experiment to bring an objective result. PEM: "We want to look at the universe as we take a "chunk" out of it! As a second point we have only one universe we can look at. We have to test models as much as possible."

Looking at the Milky Way in a clear night sky, we see a fuzzy grayish band (galaxies). Explaining Olber's Paradox : If we have an infinite universe, we can see infinite numbers of galaxies, stars behind each other, which would make the sky look bright. PEM explains Heinrich Olbers' theory with an analogy: Pictures of trees, (shown as layers on the overhead projector) while stepping back further and further away, you will see a covered area, spaces in between are not visible anymore, only green. ("You can't see the forest for trees"). You can see the same effect with the stars and galaxies. As we look into the creation mythology of northern China, we picture the cosmic egg. Like Olbers' conclusion: The universe is limited. But is it really?

What is the size of the observable universe? While astronauts see the earth huge, comparing to the universe with a scale of 1 to 10 Billion, the size of the earth is a head of a pin, the sun is a styrofoam ball of 14 cm at a distance of 15m (twice the size of our seminar room), the outermost planets would be out to Granite Bank, (Jupiter = marble, Saturn's rings = a quarter size). The closest star would be at the distance of San Francisco. We see Alpha Centauri from 4 years ago.

Saturn is 10 times as far as the sun, Alpha Centauri another factor of 20,000 times away. The size of the Milky Way Galaxy is another 20,000 larger. At the beginning of the century scientists could only map 20,000 light years, dust had been blocking the view, there seemed to be nothing. Nowadays better measurements made it possible to map even beyond 100,000 light years (= whole Milky Way Galaxy). There is much more empty space between the sun and stars than between the galaxies. Comparing the distance of the Andromeda and the Milky Way Galaxy, they are only two arms lengths apart with the size of dessert plates. The size of the observable universe is 15 Billion light years.

Edwin Hubble found that more distant Galaxies move faster from us than Galaxies which are closer from us. But all move away. The velocities can be determined with spectral lines. When light sources (Galaxies) move away from us they shift more into the direction of red. If they would come towards us they would be blue. As an analogy: comparing the horn of a car coming towards us has a high pitch, the horn of a leaving car has a low pitch.

Looking at pictures of galaxies, all galaxies are moving away from each other, so that it appears to us being in the center. ( The center can be anywhere.) The picture of a Stollen, a Christmas cake baked from rising yeast dough, lets us understand the expanding universe with it's raisins as galaxies.

PEM: Our universe has an age of 10 - 15 Billion years. There is a limit even for stronger telescopes. The light could not reach us yet. If you have an infinite universe, you cannot see for ever. You can only see 15 Billion light years and not more. We have a finite observable universe. This resolves Olbers'Paradox.

PEM: Space is expanding like the yeast dough, dough is finite. (Imagine yourself sitting on a raisin as you watch the dough and other raisins expanding around you, if you sit at the crust...too bad, you fall off!) You cannot know the center, but you can talk about the center as the observable universe.

PEM: We cannot send information through space, which travels faster than speed of light.

PEM: We don't know whether the universe is accelerating or decelerating. A universe full of masses has gravity. Thinking of an analogy: a rocket needs the speed of 11.2 km per sec. to leave the earth, with the earth 0.5 of the mass the rocket would escape, with the earth 2 times of mass the rocket would return. We measure the escape velocity. Having not enough mass in the universe it expands forever, when too much mass it will collapse sometime in the far future. That means that it would decelerate. But there are scientists talking about an accelerating expansion. That would mean that the force of the "Big Bang"is still operating. (Einstein once mentioned about this: "This is the biggest blunder of my life!"- he plucked this into his equations.)

If we curve an open universe with no boundaries in a two dimensional world (flat earth) to a curved one, we think of the balloon as an analogy. The 3 dimensions are curved into 4 dimensions forced by the gravitation of mass in the universe. No boundaries are found in the saddle geometry (like horse saddle shape), which expands forever. That would be a truly infinite universe.

PEM: Yes, every compression means also heat!


Next time we will continue with the hot universe.

*** Thank you for the student who served the slide projector! Hannelore Moebius