How to Measure Space

Optical telescopes let us examine objects within the visible light spectrum but are relatively weak tools. That’s because the light from distant galaxies can intercept clouds of particles and other bodies before reaching Earth. Other devices can measure wavelengths that fall well outside the visible spectrum. Many of the recent studies in cosmology focus on the cosmic microwave background (CMB). The CMB is radiation that the universe generated when it was only 380,000 years old [source: Luminet]. By studying this radiation, cosmologists can draw conclusions about what the universe was like shortly after it began.

Using the Wilkinson Microwave Anisotropy Probe (WMAP), scientists made an interesting discovery about the CMB. They found that the variation in radiation wavelengths of the CMB stops at a certain point. In an infinite, unbounded universe, there would be no limit to the size of wavelengths. We would expect to see variation and frequencies at all sizes. It’s only in a finite universe or a very specialized infinite one that we’d expect to see a definitive cap on wavelengths.

 

Music to My Ears
In harmonics, a plucked string produces a sound with a wavelength twice the length of the string. You couldn’t produce a sound with a wavelength longer than that. In space terms, the absence of longer radiation wavelengths leads some cosmologists to believe that the universe has a finite boundary.

 

As for expansion, cosmologists call the ratio of the amount of matter in the universe and the amount needed to stop expansion the density parameter. A density parameter greater than 1 would mean a closed universe -- there is more mass in the universe that would be needed to reverse expansion. A density parameter of 1 would mean a flat universe in which expansion slows but never truly stops. And a density parameter between 0 and 1 would mean an open universe that would continue expanding forever.

­But we don’t know how much matter really is in the universe. The amount we can detect is relatively small -- 5 percent of the matter needed to reverse expansion. But there appears to be matter that we can’t see at all. Cosmologists have noticed that stars move in an odd way -- they behave as if there is more matter exerting a gravitational influence on them than we can detect. Some cosmologists theorize that this means there is a kind of matter we can’t see at all, called dark matter.

 
Visible, or baryonic matter
Courtesy STScI
and NASA
Visible, or baryonic matter
 
­Dark Matter
Courtesy STScI
and NASA
Dark Matter
 

­But is there enough dark matter to cause a big crunch? That is, is there enough ­matter in the universe to make up the balance and push the ratio to a 1 or higher? While cosmologists believe there is far more dark matter in the universe than observable matter, they estimate the combination of both visible and dark matter still only comes to about 30 percent of the amount needed to reverse expansion [Source: String Theory Web Site].

 

Before the Big Bang?
What happened before the big bang? It’s impossible to say. Scientists theorize that once you compress the matter of the universe into a singularity (a point with zero volume but infinite density), scientific laws can no longer apply. Since the laws of physics are moot, there is no way to know what, if anything, came before the big bang. Science can’t answer the question.

 

While we don’t know what the definitive shape of space is right now, research continues to bring us new information every day. And if space has boundaries, what lies beyond them? We don’t know, and we may not be capable of knowing.

Want to learn more about space and related topics? Set a course for the links on the following page.