In the current, best model for the universe, the universe was created in the Big Bang event 12 to 15 billion years ago. Let's call it 12 billion years.
Twelve billion years, that's a lot! But that's just some big number, it probably doesn't mean any more to you than would 100 billion years or 12 million years. Is there some way to put this age into a more meaningful perspective?
Imagine the entire history of the universe, from the Big Bang to the present moment, was one year of time. The 12 billion years of history compressed down into 12 months, each month represents 1 billion years.
On this compressed time scale, some notable events are:
| January 1, 12 am | Big Bang occurs |
| Early February | Our Milky Way Galaxy forms |
| August 12 (approx.) | The Earth and Sun are formed |
| September 28 (approx.) | First life arises on the Earth |
| December 13 | First animals appear on Earth |
| December 25 | Dinosaurs now walk the Earth |
| December 30, 12:33 am | Dinosaurs wiped out by asteroid collision |
| December 31, 9:00 pm | First humanoid life appears |
| December 31, 11:58 pm | Homo Sapiens first appear |
| December 31, 11:59 pm + 30 seconds | Agriculture developed |
| December 31, 11:59 pm + 47 seconds | Pyramids built |
| December 31, 11:59 pm + 59 seconds | Shakespeare writes plays |
The universe is so old that all of recorded human history occupies only the last 13 seconds or so of the year.
The universe may be infinite in size, or it may be of only finite size. Doesn't the universe have to be infinite? It doesn't make any sense that it would be finite, then there would be some end or edge, and what would be beyond that?
Strange as it may seem, the universe could be finite, a finite universe would not have to have any edges or an end, it could 'wraparound'. The universe could be curved. Huh? How could you curve the universe?
An analogy should help, consider the surface of the Earth. It looks flat and many children and ancient people might assume that it is flat and that it is either infinite or must have an end or edge somewhere.
But the Earth's surface is curved, it wraps around and closes in on itself. There is only a finite amount of area yet there is no ends or edges. The two-dimensional flat surface of the Earth is wrapped around into a sphere when viewed in three dimensions. If you set out flying westward in a plane, you will wraparound and eventually return to where you started, approaching from the east.
The universe may be a curved three-dimensional space that wraps around and closes on itself. If you set out in a spacecraft heading one direction, you could eventually return to the same spot from the opposite direction.
A nice demonstration of the scale of the universe is to start with a view showing our galaxy and then zoom by a factor of ten once per second. Such a demonstration is done at http://micro.magnet.fsu.edu/primer/java/scienceopticsu/powersof10/
Click on this link and view the demo. Use your browser's
Back button to return to this page after watching the demo.
The entire universe, or just the visible portion of the universe if its infinite, is roughly 27 billion light-years across. That's 159,000,000,000,000,000,000,000 miles. Our solar system, from the Sun to Pluto, is .00063 light-years across or 3,720,000,000 miles. That makes our solar system 42,700,000,000,000 times smaller than the whole universe.
Can we put that into a more meaningful perspective? If the entire Earth's surface represents the whole universe, the solar system on that scale would be one-millionth of a meter wide, about 1/25,000 of an inch, the size of a single, small bacteria.
The Earth* |
E. Coli bacteria* |
And that bacteria is the whole solar system, imagine how much smaller the Earth and people are on that scale!
The universe is full of stars, arranged in enormous groups called galaxies. Our Sun is one star among 100 billion in the Milky Way Galaxy. And there are about 100 billion galaxies in the universe, each with a comparable number of stars.
With some simple math, we can figure out the total number of stars in the universe:
(100 billion stars/galaxy) x (100 billion galaxies) = (100 x 10^9) x (100 x 10^9) = 10^22 stars
How many is that? The number of stars in the universe is more than the number of grains of sand on all the beaches of the entire Earth! More stars than there are grains of sand! Think about that.
Only in the last few years have astronomers had the technology with which to discover planets around nearby stars. It does seem that most stars do have planets - although those planetary systems do not closely resemble our own solar system.
We can only barely tell that these other planets exist, we do not yet have the technology to determine if any life exists on these planets. So far no life has been discovered on any other planet but when you ponder on the number of stars that there are, it seems inevitable that there will be life on other planets.
How big is the Earth compared to the Sun? Compared to Jupiter?
How far is it from the Earth to the Moon compared to the Earth to the Sun?
To answer these questions and more, we will make a scale model of the solar system.
We'll scale the solar system so that everything is 8 billion times smaller. This reduces every 80,000 km of distance down to 1 cm. Using this conversion, calculate all the following scale sizes and distances.
This is most easily done as a mathematical
conversion, where 80,000 km = 1 cm outside. For example, (4878 km) (1 cm
/ 80,000 km) = .061 cm. That is, you just divide all the numbers by 80,000.
Planet |
Actual Diameter |
Dist. from |
Scaled |
Dist. from |
|
| Sun | 1 392 000 |
N/A |
N/A | N/A | |
| Mercury | 4 878 |
57 900 000 |
.061 | ||
| Venus | 12 104 |
50 300 000 |
|||
| Earth | 12 756 |
41 400 000 |
|||
| Mars | 6 794 |
78 300 000 |
|||
| Jupiter | 142 984 |
550 500 000 |
|||
| Saturn | 120 536 |
645 600 000 |
|||
| Uranus | 51 118 |
1448 000000 |
|||
| Neptune | 50 538 |
1627 000000 |
|||
| Pluto | 2 280 |
1444 000000 |
Sun-Alpha Centauri = 4.2 x 10^13 km = ____________________
(This scaled distance is over 3000 miles!)
Now, to get a better feel for how big (and empty!) the solar system is, you should go outside and walk off the distances (that's why you calculated the number of paces). You'll need something (about 7 or 8 inches across) to be the sun and a clear walking stretch about half a mile long.
Some notes about the Solar System and our model:
* In the real solar system, the planets can be anywhere around the sun,
they don't line up like we have them.
* When at the Earth's location, the scale Sun should occupy the same angular
size in your field of view that the Sun does in the actual sky.
* The solar system is a very empty place.
* Asteroids and comets are generally very small objects, in our scale model
they would be microscopic. Exception: when comets are close to the Sun,
their comas and tails are enormous. The coma of a comet can be as large
as Jupiter and the tail can stretch as far as the Earth-Sun distance.
*Earth picture from NASA web site.
*E. Coli picture from commtechlab.msu.edu/sites/dlc-me/zoo/zah0700.html