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Scales in space and time
Scales in space and time

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2.1 The Universe

This video provides a brief history of the Universe and gives details of its age and size today. The questions that follow will help you discover the time and space scales that correspond to the biggest and oldest objects in the size–time explorer. First you will look at describing the age and size of the Universe in SI units, and then consider how quickly some of the early occurrences in the Universe took place.

While watching the video, record the following information to use in the questions that follow:

  • the age of the Universe today
  • the diameter of the Universe today (in metres)
  • the times that events occurred since the big bang.
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Transcript: Origins of the Universe

JULIA COOKE
The universe is the biggest and oldest thing we know. It contains all existing matter and space. And its origin marks the beginning of time as far as we understand it. We don’t know what made the formation of the universe possible, nor why it occurred. The visible universe is currently about 93 billion light years wide. A light year is the distance that light travels in a year, which makes the universe about 880 trillion trillion metres wide.
The visible universe is, however, still expanding, and we can measure that rate of expansion. Then, working backwards, we can figure out when the universe would have begun. To the best of our knowledge, the universe formed about 13.8 billion years ago in what is commonly referred to as the Big Bang. This image shows the universe about 370 000 years after the Big Bang, which is the oldest light that we’ve been able to record with the greatest precision.
The image records ancient light, or cosmic microwave background. The colours show tiny temperature fluctuations from an average temperature. These indicate areas of different densities, which became the stars and galaxies of today. Red spots are a bit hotter and blue spots a bit cooler. The image was recorded between 2009 and 2013, during the Planck mission, when the space observatory was operated by the European Space Agency, in conjunction with NASA, the National Aeronautics and Space Administration.
Today, the universe is very cold. On average, it is 2.7 Kelvin. Kelvin is a measure of temperature with the same magnitude as degrees Celsius. But 0 Kelvin equals minus 273.15 degrees Celsius. In the universe the hot parts, such as stars, make up only a tiny fraction. If we wind the clock backwards, the universe gets smaller. And this means the universe was hotter in the past. When matter gets hot, solids melt and liquids boil. The hot matter glows – red at first, but it becomes bluer as the temperature goes up. Eventually, all matter is gas. So we have a bright, glowing blob of gas.
Going further back in time, as the gas gets hotter, the electrons are separated from the nuclei and a plasma is made. The temperature at this point is about 3000 to 6000 Kelvin and the glowing blob is white hot. As we go back further in time, the universe gets even smaller and hotter. The nuclei themselves, containing protons and neutrons, are broken up. The reason for the breakup of nuclei is that the individual particles and the energy of the radiation is so great that the collisions of all this hot stuff are incredibly violent. The light is no longer in the visible spectrum. It is energetic enough to be x-rays and even gamma rays.
Between just 10 seconds and 1000 seconds after the Big Bang, subatomic particles, including neutrons and protons, were formed. Neutrons live for just 9 minutes when they are free. Hence only those that stuck to protons during this period survived. All of the ordinary matter present today formed in this short window of time. At about 1 microsecond after the Big Bang, the universe was very hot, at 10 to the 10 Kelvin, and quarks formed stable particles called hadrons.
Before 1 picosecond, or 10 to the minus 12 seconds, the universe was an exotic place. The gas was hotter still and the laws of physics appeared different to how we see them today. The distinction between matter and radiation, such as light, cannot be detected. The forces of electromagnetism and the weak nuclear force also become indistinguishable. At the very earliest times, the universe was so hot and dense that we cannot yet describe them accurately.
End transcript: Origins of the Universe
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Origins of the Universe
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Question 1

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Question 2

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Question 3

Use your notes from the video to identify which of the following two tables correctly describes the events and temperatures that occurred after the big bang:

Table 3A
Event Temperature/K Time since big bang/s
big bang unknown 0
neutrons and protons formed ~100 000 10−6
quarks exist in a plasma 100 000 000 000 10−12
quarks and other fundamental particles form stable particles 10 000 000 000 000 10–1000
today 2.7 × 1017
Table 3B
Event Temperature/K Time since big bang/s
big bang unknown 0
quarks exist in a plasma 10 000 000 000 000 10−12
quarks and other fundamental particles form stable particles 100 000 000 000 10−6
neutrons and protons formed ~100 000 10–1000
today 2.7 × 1017

Answer

Table 3B is correct. It shows the correct combination of events, temperatures and times, with the universe cooling over time, and the times listed in a logical order.

Question 4

Use the information from Question 3 to consolidate your learning and fill in the missing gaps in the paragraph below.

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Summary

Here, you learned about the current size of the Universe and its age, as well as it origin by working backward through time. The Universe is the biggest thing known, but considering how it began requires you to think about some of the very smallest things known, including subatomic particles such as protons and neutrons.

Next: That’s as big as possible! Now return to the size–time explorer [Tip: hold Ctrl and click a link to open it in a new tab. (Hide tip)] to choose your next level of scale, or use the ‘Next >’ button to go to the next level down on the size scale.