<< Chapter < Page Chapter >> Page >
A pie chart shows 26.8 percent dark matter, 4.9 percent atoms and 68.3 percent dark energy.
Estimated distribution of matter and energy in the universe. (credit: NASA/WMAP Science Team)

Summary

  • The early universe was hot and dense.
  • The universe is isotropic and expanding.
  • Cosmic background radiation is evidence for the Big Bang.
  • The vast portion of the mass and energy of the universe is not well understood.

Key equations

Momentum of a charged particle in a cyclotron p = 0.3 B r
Center-of-mass energy of a colliding beam machine W 2 = 2 [ E 1 E 2 + ( p 1 c ) ( p 2 c ) ] + ( m 1 c 2 ) 2 + ( m 2 c 2 ) 2
Approximate time for exchange of a virtual particle between two other particles Δ t = h E
Hubble’s law v = H 0 d
Cosmological space-time metric d s 2 = c 2 d t 2 a ( t ) 2 d Σ 2

Conceptual questions

What is meant by a “cosmological model of the early universe?” Briefly describe this model in terms of the four fundamental forces.

Got questions? Get instant answers now!

Describe two pieces of evidence that support the Big Bang model.

The observed expansion of the universe and the cosmic background radiation spectrum.

Got questions? Get instant answers now!

In what sense are we, as Newton once said, “a boy playing on the sea-shore”? Express your answer in terms of the concepts of dark matter and dark energy.

Got questions? Get instant answers now!

If some unknown cause of redshift—such as light becoming “tired” from traveling long distances through empty space—is discovered, what effect would that have on cosmology?

If light slow down, it takes long to reach Earth than expected. We conclude that the object is much closer than it really is. Thus, for every recessional velocity (based on the frequency of light, which we assume is not disturbed by the slowing), the distance is smaller than the “true” value, Hubble’s constant is larger than the “true” value, and the age of the universe is smaller than the “true” value.

Got questions? Get instant answers now!

In the past, many scientists believed the universe to be infinite. However, if the universe is infinite, then any line of sight should eventually fall on a star’s surface and the night sky should be very bright. How is this paradox resolved in modern cosmology?

Got questions? Get instant answers now!

Additional problems

Experimental results suggest that a muon decays to an electron and photon. How is this possible?

Got questions? Get instant answers now!

Each of the following reactions is missing a single particle. Identify the missing particle for each reaction.

(a) p + p n + ? (b) p + p p + Λ 0 + ? (c) π + p Σ + ? (d) K + n Λ 0 + ? (e) τ + e + + υ e + ? (f) υ e + p n + ?

a. n ; b. K + ; c. K + ; d. π ; e. ν τ ; f. e +

Got questions? Get instant answers now!

Because of energy loss due to synchrotron radiation in the LHC at CERN, only 5.00 MeV is added to the energy of each proton during each revolution around the main ring. How many revolutions are needed to produce 7.00-TeV (7000 GeV) protons, if they are injected with an initial energy of 8.00 GeV?

Got questions? Get instant answers now!

A proton and an antiproton collide head-on, with each having a kinetic energy of 7.00 TeV (such as in the LHC at CERN). How much collision energy is available, taking into account the annihilation of the two masses? (Note that this is not significantly greater than the extremely relativistic kinetic energy.)

14.002 TeV 14.0 TeV

Got questions? Get instant answers now!

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.

Got questions? Get instant answers now!
Practice Key Terms 4

Get Jobilize Job Search Mobile App in your pocket Now!

Get it on Google Play Download on the App Store Now




Source:  OpenStax, University physics volume 3. OpenStax CNX. Nov 04, 2016 Download for free at http://cnx.org/content/col12067/1.4
Google Play and the Google Play logo are trademarks of Google Inc.

Notification Switch

Would you like to follow the 'University physics volume 3' conversation and receive update notifications?

Ask