Quoting from Alan Lightman's "A MODERN DAY YANKEE IN A CONNECTICUT
      COURT and other essays on Science". 
      
      Conversations with Papa Joe
      
      The Second Evening 
      
      "The next evening, I hurried through dinner
      and, about eight o'clock, went to my study. I lit up my pipe and
      drew furiously, filling the room with great clouds of smoke, but
      nothing happened. Then, when I was starting to feel dizzy, Papa
      Joe appeared, just as he had the night before. He stood tall and
      erect for a moment and then sat down across from me, in his
      chosen chair.

      For a while neither of us spoke. Papa Joe seemed to be enjoying
      the aromas wafting from the pipe, and I hated to interrupt his
      pleasure. I'd filled the pipe with my own blend of cavendish and
      burley, but, as happens with a fine old briar, all the tobaccos
      he'd ever smoked in it had left their own flavors inside the bowl
      and were now drifting through the room.

      "I'm happy you came back," I finally said. "I hope our
      conversation last night didn't upset you."

      "I must admit, your modern view of the heavens takes some getting
      used to. It strains me to picture a galaxy and its billions of
      suns. I have a much easier time picturing a house, with the plans
      and drawings all in front of me."

      "Perhaps that's because you've put up a lot of houses with your
      own hands. You know how the marks on the drawings will turn into
      windows and doors."

      "Just what I was getting at," said the old gentleman. "It seems
      that your astronomers want me to imagine an enormous building
      I've got no way of touching, and neither do they. All they've
      given me for blueprints are photographs of small white dots, and
      arguments. The reasoning is sound, I'll agree, but I keep
      remembering Aesop's astronomer, who walked outside every night
      looking up at the sky, until one night he fell into a well."

      "Don't worry. " I said laughing, "we won't have to venture from
      our chairs. We can continue last night's tour just fine from
      where we're sitting."

      "Good, lets go on. You left off with the galaxies, far apart like
      little islands in space, except they're not little."

      "Now you have to imagine that these galaxies are flying away from
      each other a great speed," I said. "That we learned about fifty
      years ago from Professor Hubble, who discovered that galaxies
      appear redder than they should be if they were standing still."

      "Hold on, you've lost me."

      "Let me try and explain with an analogy to sound. When something
      making a sound moves, the pitch of the sound changes. It goes up
      when the thing's coming toward you, and down when it's going
      away. The faster the speed, the greater the shift in pitch.
      You've probably noticed the effect with a passing train. When
      it's approaching, the pitch of its whistle rises, and when it's
      going away the pitch drops."

      The old gentleman nodded. "I know trains pretty good. The L. and
      N. ran next to my quarry. Many times I heard that falling shriek
      as it passed, but I never thought much about it."

      "Well, the same kind of thing happens with light," I went on. "In
      light, what corresponds to pitch is color. When a source of light
      is moving toward you, its color goes up in frequency, which means
      it becomes bluer. When it's moving away, it gets redder. At
      ordinary speeds, the change in color is so slight that your eyes
      can't see it, but certain very sensitive instruments can. Hubble
      had one of these fastened to his telescope while he was studying
      galaxies. When he found that their colors were shifted toward the
      red, he concluded the galaxies were traveling away from him in
      all directions. What's happening, we believe, is that every
      galaxy is rushing away from every other galaxy, like dots painted
      on an expanding balloon. The whole universe is expanding."

      "Hold on, young man. You understand this business of colors much
      better than I do, but it seems to me that if the galaxies are
      flying off, we should see them move in our telescopes. Shouldn't
      we?"

      "Not if they're very far away, " I replied. "Motion at a great
      distance is hard to detect. Galaxies are so far away they seem to
      be standing still, even in telescopes. Fortunately, we have our
      spectrometers."

      "I'm beginning to feel better and better about being anchored to
      this chair, with the universe flying apart all around me," said
      Papa Joe, "I never guessed so much commotion was going on out
      their."

      "You're in with some good company," I replied. "Aristotle
      convinced everybody the universe was perfectly steady, and people
      believed him for two thousand years. He had some exhausting
      arguments, and there wasn't any evidence to the contrary--not
      until Professor Hubble."

      "And if I understand you," said Papa Joe, "you're saying that
      after all those centuries of peaceful nights under the stars,
      your modern astronomers have decided that Creation is bursting
      apart, on the strength of some gadgets looking a little smudges
      of light through a telescope."

      "That's what I'm saying. And I believe it, although I admit it
      goes against what I see when I look up at the sky." I got up and
      took out a pipe cleaner from my desk near the window. My
      great-grandfather sat working his moustache.

      "I reckon common sense isn't worth much in this business," he
      mused.

      "It seems to me, " I replied, "that common sense is what you
      learn from personal experience. But we're talking about things
      that you can't possibly experience, not with your human senses
      anyway. A good deal of science these days is beyond the senses,
      and it isn't at all common. The only way to get there is to start
      with what you're dead sure about, then climb out a bit, standing
      on solid logic, then climb a little further, inching your way
      along and making certain each step is firmly supported by the one
      below. Sometimes you take what you thought was a little step and
      find yourself hanging in thin air. Then you have to grab on and
      scramble back a few rungs. One way or another, you eventually get
      so far up you can't see where you started. That's when you need
      to have faith."

      "I'll bet nothing compares to that feeling of being up in the
      clouds'" said Papa Joe, "with the ground out of sight, and
      knowing the strength of your ladder. That must be how Shapley
      felt. And Hubble. I wish I'd been there."

      I nodded. "So do I. Those guys had faith--but well-grounded faith,
      I believe. Take Hubble's, for example. The same spectrometers we
      point at galaxies we also point at lightbulbs set up in the lab,
      where we're darn sure whether the lightbulbs are moving or not,
      and how fast. The theory checks out. So if galaxies aren't flying
      apart as we think, then the laws of nature in space are different
      from what the are on the ground.  That would be illogical. If one
      and one makes two over here, one and one should make two over
      there. Or else all science would be in a terrible mess, and
      scientists would be out of work. Let's assume D. Hubble was
      right, " I continued, "and the universe is expanding. That means
      it was smaller and denser in the past."

      Papa Joe nodded cautiously, like a man readying himself for the
      pinch of a used-buggy salesman.

      "Then if you mentally go backward in time," I went on, "the
      galaxies get closer and closer together. Eventually, they touch
      and merge and become a single mass, which gets denser and
      denser.  Planets and stars lose their boundaries. Atoms get
      ripped apart and crushed together. Everything gets squeezed
      closer and closer together. Finally, there comes a definite time
      in the past when all the matter of the universe is compressed
      into a single point.  Astronomers can estimate that time by
      measuring how fast the universe is expanding now. It's about 14
      billion years ago. 14 billion years ago, according to the
      theory, the universe exploded from a point and was born.
      Scientists call that beginning the Big Bang."

      The old gentleman was busily working his moustache again.
      Furthermore, he had abandoned the safety of his chair and was
      pacing the room, narrowly missing the logs piled by the
      fireplace. "On the strength of some gadgets looking at little
      smudges of light through a telescope," he muttered. "I used to
      think I had chutzpah."

      "It comes with the profession these days, " I said. Just then, a
      church clock struck ten in the distance. Papa Joe produced from
      his vest pocket a beautiful gold watch, flipped open its cover,
      and nodded appreciatively. When he saw how taken I was with his
      watch, he handed it to me to look at more closely. The he began
      complaining again about the Big Bang.

      "There's something else that adds weight to this ten billion
      years," I offered. "Stars and planets began forming soon after
      the universe began, so the earth has to be younger than the
      universe, but probably not a lot younger. At the beginning of the
      century, before people had any idea of a Big Bang, some chemists
      found a way to tell how old the earth is.  Special kinds of atoms
      are continuously changing into other kinds of atoms, in a regular
      way. For example, uranium atoms change into lead atoms. If you
      start off with a rock of pure uranium, after a certain number of
      years half of it will be lead. After that number of years again,
      three quarters of it will be lead, and so on. So by measuring how
      much uranium and how much lead are in the rock at any point in
      time--and assuming the laws of nature don't change in time--you
      can figure how long it's been since the rock was pure uranium.
      About twenty years before Hubble made his measurements on
      galaxies, some chemists dug up a few rocks, part uranium and part
      lead, and used them to estimate the age of the earth. It came out
      to about four and a half billion years, nearly a third the age of the 
      universe, according to Hubble. In other words, the figure that astronomers
      get by looking at far-off galaxies through a telescope is roughly
      the same as what chemists and geologists get by looking at rocks
      under their feet. It amazes me how those two numbers agree."

      "An interesting story," said my great-grandfather. "The faith of
      one scientist holds up the faith of another. That's good. But
      it's still faith, as you were saying before. You can measure you
      atoms and galaxies until hell freezes over, but I doubt if you're
      going to know for sure how old the universe is, or even if it has
      an age."

      "Not by being there at the start," I had to admit. "the entire
      recorded history of human beings goes back only ten thousand
      years. Our whole species goes back only a hundred thousand."

      I was getting drowsy, and the fire was low. As I lazily rose from
      my chair to put another log on the fire, I turned and noticed
      that Papa Joe was also beginning to fad. He was standing in front
      of a bookshelf, lost in thought, and various titles slowly
      started to appear through his dissolving form--WALDEN, THE DOUBLE
      HELIX, A CONNECTICUT YANKEE IN KING ARTHUR'S COURT. I hoped he
      would come back again.

                              To Be Continued