The Big Bang’s Leftovers
The Big Bang’s Leftovers Tell Us About The Universe Today . The hot
Big Bang might have started our Universe as we know it some 13.8 billion
years ago, but there’s a piece of it still visible to us today. Because
the “bang” happened everywhere at once, there’s light that’s been
traveling in all directions for 13.8 billion years, and some of it is
just arriving at our eyes today. Because the Universe has been expanding
this entire time, the wavelength of that initially
hot light has gotten stretched, all the way from gamma rays through
visible light and into the microwave portion of the spectrum. This
leftover glow from the Big Bang shows up today as the Cosmic Microwave
Background, or CMB. Today, it’s perhaps the best piece of evidence we
have for what the Universe is made of.
The fluctuations in the CMB give rise to the Universe’s structure as it exists today.
When it was first detected back in 1965, it was an incredible confirmation of the idea that the Universe came from a hot, dense, uniform state, with its temperature and spectrum matching the theory’s predictions exactly. But as our ability to measure the CMB’s imperfections grew and grew, we learned more than anyone in 1965 could have imagined. On average, the Big Bang’s leftover glow gives us a Universe whose temperature is 2.725 K, just a few degrees above absolute zero. But there are imperfections in that temperature as well if we look in different directions. They’re very small compared to the average temperature, with the “largest” imperfection coming in at just 3 millikelvins (mK).
The details in the Big Bang’s leftover glow have been progressively better and better revealed by improved satellite imagery.
COBE,
the first CMB satellite, measured fluctuations to scales of 7º only.
WMAP was able to measure resolutions down to 0.3° in five different
frequency bands, with Planck measuring all the way down to just 5
arcminutes (0.08°) in nine different frequency bands in total.
This characteristic pattern — that it’s “hotter” in one direction and “cooler” in the opposite one — tells us how fast we’re moving through the Universe, relative to the rest frame of the expanding Universe. But if we subtract that out, we find that we have to go down to much smaller-magnitude fluctuations to find the temperature differences: microkelvin (µK) scales. If we go down that far, we get a snapshot of the tiny gravitational imperfections in the very young Universe. Thanks to the Planck satellite, we can see these imperfections down to angular scales of less than 0.1º.
The
cold spots (shown in blue) in the CMB are not inherently colder, but
rather represent regions where there is a greater gravitational pull due
to a greater density of matter, while the hot spots (in red) are only
hotter because the radiation in that region lives in a shallower
gravitational well. Over time, the overdense regions will be much more
likely to grow into stars, galaxies and clusters, while the underdense
regions will be less likely to do so.
(Image credit: E.M. Huff, the SDSS-III team and the South Pole Telescope team; graphic by Zosia Rostomian)
While these images might look like nothing more than noise to your eyes, there’s actually a tremendous amount of data packed in there. Imagine that you could divide the sky up a certain number of independent ways: 5, 15, 25, 150, etc., and measure how large the mean temperature fluctuation is on each and every scale. Every force and component of energy present in the Universe, including protons, neutrons and electrons, dark matter, radiation, dark energy, gravitational imperfections and more will influence how the fluctuations behave on each and every scale.
The fluctuations in the CMB give rise to the Universe’s structure as it exists today.When it was first detected back in 1965, it was an incredible confirmation of the idea that the Universe came from a hot, dense, uniform state, with its temperature and spectrum matching the theory’s predictions exactly. But as our ability to measure the CMB’s imperfections grew and grew, we learned more than anyone in 1965 could have imagined. On average, the Big Bang’s leftover glow gives us a Universe whose temperature is 2.725 K, just a few degrees above absolute zero. But there are imperfections in that temperature as well if we look in different directions. They’re very small compared to the average temperature, with the “largest” imperfection coming in at just 3 millikelvins (mK).
The details in the Big Bang’s leftover glow have been progressively better and better revealed by improved satellite imagery.
COBE,
the first CMB satellite, measured fluctuations to scales of 7º only.
WMAP was able to measure resolutions down to 0.3° in five different
frequency bands, with Planck measuring all the way down to just 5
arcminutes (0.08°) in nine different frequency bands in total.This characteristic pattern — that it’s “hotter” in one direction and “cooler” in the opposite one — tells us how fast we’re moving through the Universe, relative to the rest frame of the expanding Universe. But if we subtract that out, we find that we have to go down to much smaller-magnitude fluctuations to find the temperature differences: microkelvin (µK) scales. If we go down that far, we get a snapshot of the tiny gravitational imperfections in the very young Universe. Thanks to the Planck satellite, we can see these imperfections down to angular scales of less than 0.1º.
The
cold spots (shown in blue) in the CMB are not inherently colder, but
rather represent regions where there is a greater gravitational pull due
to a greater density of matter, while the hot spots (in red) are only
hotter because the radiation in that region lives in a shallower
gravitational well. Over time, the overdense regions will be much more
likely to grow into stars, galaxies and clusters, while the underdense
regions will be less likely to do so.(Image credit: E.M. Huff, the SDSS-III team and the South Pole Telescope team; graphic by Zosia Rostomian)
While these images might look like nothing more than noise to your eyes, there’s actually a tremendous amount of data packed in there. Imagine that you could divide the sky up a certain number of independent ways: 5, 15, 25, 150, etc., and measure how large the mean temperature fluctuation is on each and every scale. Every force and component of energy present in the Universe, including protons, neutrons and electrons, dark matter, radiation, dark energy, gravitational imperfections and more will influence how the fluctuations behave on each and every scale.
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