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The Inflatable Universe

Full microwave sky view in a Mollweide projection

A 12 inch inflatable globe (beach ball) can be used as a model of the

observable universe. The ball's surface represents the furthest we can see in

microwave light, the oldest visible light in the universe. The ball presents the

baby picture created just 379,000 years after the Big Bang, 13.7 billion years

ago, before planets, stars or galaxies existed! The patterns imply a universe

dominated by a mysterious "dark energy" and an exotic "dark matter." This full

sky image of microwave light was captured by the Wilkinson Microwave

Anisotropy Probe (WMAP).

Single copies of this specially prepared inflatable ball (and explanation card)can be obtained for education purposes from a NASA's Imagine the Universe

Teachers' Corner . Other inquiries can be sent through our contact page.

Hot and Cold Spots

The colors indicate temperature variations of light within the young universe,

red for hotter, blue for cooler. These slight variations of temperature were

caused by slight variations in the density of the matter from which the light was

last scattered. But the red stripe along the globe's equator is a much more

recent/closer/stronger foreground microwave signal from our Milky Way Galaxy.

The sizes of the hot and cold spots let scientists calculate fundamental values

for the shape, size, age, rate of expansion (and more) of our universe.

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If the microwavelight were shiftedup to the visiblespectrum and

amplified, our eyewould see a

colorful rainbow of spots across the

whole sky.

2.7251 kelvins

2.7249 kelvins

12-inch Model of the Universe

The 12 inch ball (with a 6 inch radius) can represent the distance light has been

able to travel in the nearly 13.7 billion years since the matter of the universe

cooled to less than 3000 kelvins. We are at the center of this bubble of light, but 

many more times this volume of space exists outside this bubble, we just can

not yet see its light. Every year the bubble of the observable universe grows alittle larger as new light reaches our eyes. The bubble expands as the fabric of 

space itself stretches. Light stretches and cools (akin to distributing the same

amount of energy within a continually expanding oven) toward the ultimate

chilly "absolute zero" temperature (0 kelvins).

Long Description

The light from the first stars appeared roughly 400 million years after the Big 

Bang. Yet in the model above it is a much larger distance in from the edge of 

the ball (about 10 billion light years). This is the result of the expanding fabric of 

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space. The universe was more compressed, but expanding more rapidly than it 

is today.

What WMAP Sees

The temperature difference measured now between the coldest and hottest 

spots is extremely small, but the early universe was very hot. When the

average density of matter in the universe was comparable to air at sea level, its

temperature was 2.73 billion degrees! (The average density today is the

equivalent of about one proton per cubic meter.) At these temperatures, protons

and electrons could not bind together to form neutral atoms. The free electrons

scattered the cosmic background radiation much as water drops scatter visible

light in clouds, so the early universe would appear as a dense fog. As the

universe expanded, it cooled. 379,000 years after the Big Bang, it was cool enough for protons and electrons to combine into neutral hydrogen. Neutral 

hydrogen is transparent, so the cosmic background radiation has traveled freely 

through the universe since that time.

On a cloudy day, we can look through the air to see the surface of the clouds.

Similarly, we can see through the universe out to where it was filled with free

electrons and see the “dense fog” that filled the early universe. The reason we

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can “see” the early universe is that we see objects as they were in the past due

to the time it takes light to travel across space. For example, we see the Sun as

it existed 8 minutes earlier. We see the “cloud surface” from which the cosmic 

background radiation was last scattered as it existed 13.7 billion years ago.