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Chapter 11: Problem 24

Describe the balloon analogy for cosmological expansion. Explain why it only appears that we are at the center of expansion of the universe.

Short Answer

Expert verified
The balloon analogy represents the expansion of the universe, where the surface of a balloon stands for the fabric of space, and dots on the surface represent galaxies. As the balloon inflates, the area increases, and the galaxies move away from each other uniformly. Observers on any point (or galaxy) would see other galaxies moving away in every direction, creating the illusion of being at the center of expansion. However, this is just our perspective as observers; in reality, there is no center because the expansion occurs uniformly throughout the universe.

Step by step solution

01

Understanding the balloon analogy

The balloon analogy is a way to represent the expansion of the universe in two dimensions, where the surface of the balloon represents the fabric of space. Imagine a deflated balloon with dots, representing galaxies, on its surface. As the balloon inflates, the surface area increases, and the dots (galaxies) move away from each other. The balloon itself can represent the expanding universe.
02

Observing the expansion from one point (dot)

To grasp why it appears that we are at the center of the expansion, consider yourself to be an observer on one of the dots on the surface of the balloon. As the balloon inflates, you will see all other dots moving away from you in every direction.
03

Observing the expansion from a different point (dot)

Now, let's say you are an observer on a different dot. Just like before, as the balloon inflates, you will see all other dots moving away from you in every direction too. This phenomenon occurs because the expansion is taking place uniformly throughout the surface of the balloon, and it applies to any dot, regardless of where it is on the balloon's surface.
04

Understanding why it seems we are at the center of expansion

The balloon analogy demonstrates how the expansion of space happens uniformly throughout the universe. Every point (or dot) in the universe would observe other galaxies moving away from them in every direction and think they are at the center of the expansion. In reality, there is no actual center since the expansion occurs uniformly and is not centered on any specific point. It's an illusion caused by our perspective as observers.
05

Recap of the balloon analogy and expansion appearance

In summary, the balloon analogy helps us visualize the cosmological expansion of the universe. It also highlights why it seems that we are at the center of the expansion - an illusion created by the uniform expansion of space. As observers on any point (or galaxy) in the universe, we would always see other galaxies moving away from us in every direction, leading to the perception of being at the center of the expansion; however, this is not the case, and expansion is happening uniformly in the universe.

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Most popular questions from this chapter

Draw a Feynman diagram to represents annihilation of an electron and positron into a photon.

Electrons and positrons are collided in a circular accelerator. Derive the expression for the center-of-mass energy of the particle.

Which of the following decays cannot occur because the law of conservation of lepton number is violated? (a) \(\mathrm{n} \rightarrow \mathrm{p}+\mathrm{e}^{-}\) (b) \(\mu^{+} \rightarrow \mathrm{e}^{+}+v_{\mathrm{e}}\) (c) \(\pi^{+} \rightarrow \mathrm{e}^{+}+v_{\mathrm{e}}+\bar{v}_{\mu}\) (d) \(\mathrm{p} \rightarrow \mathrm{n}+\mathrm{e}^{+}+v_{\mathrm{e}}\) (e) \(\pi^{-} \rightarrow \mathrm{e}^{-}+\bar{v}_{\mathrm{e}}\) (f) \(\mu^{-} \rightarrow \mathrm{e}^{-}+\bar{v}_{\mathrm{e}}+v_{\mu}\) (g) \(\Lambda^{0} \rightarrow \pi^{-}+\mathrm{p}\) (h) \(\mathbf{K}^{+} \rightarrow \mu^{+}+v_{\mu}\)

When an electron and positron collide at the SLAC facility, they each have 50.0 -GeV kinetic energies. What is the total collision energy available, taking into account the annihilation energy? Note that the annihilation energy is insignificant, because the electrons are highly relativistic.

Which of the following reactions cannot because the law of conservation of strangeness is violated? (a) \(\mathrm{p}+\mathrm{n} \rightarrow \mathrm{p}+\mathrm{p}+\pi^{-}\) (b) \(\mathrm{p}+\mathrm{n} \rightarrow \mathrm{p}+\mathrm{p}+\mathrm{K}^{-}\) (c) \(\mathrm{K}^{-}+\mathrm{p} \rightarrow \mathrm{K}^{-}+\sum^{+}\) (d) \(\pi^{-}+\mathrm{p} \rightarrow \mathrm{K}^{+}+\sum^{-}\) (e) \(\mathrm{K}^{-}+\mathrm{p} \rightarrow \Xi^{0}+\mathrm{K}^{+}+\pi^{-}\) (f) \(\mathrm{K}^{-}+\mathrm{p} \rightarrow \Xi^{0}+\pi^{-}+\pi^{-}\) (g) \(\pi^{+}+\mathrm{p} \rightarrow \Sigma^{+}+\mathrm{K}^{+}\) (h) \(\pi^{-}+\mathrm{n} \rightarrow \mathrm{K}^{-}+\Lambda^{0}\)
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