Considering the reactions in primordial nucleosynthesis only, what would be the impact on the universe today if the neutron lifetime were much smaller than 886s (the actual value of the neutron lifetime)? Select one: O a. Annihilations mean that the universe is left composed entirely of photons and neutrinos O b. There would be no difference to the actual universe c. Only hydrogen atoms would be present today O d. There would be very small amounts of He in the universe today

Considering the reactions in primordial nucleosynthesis only, what would be the impact on the universe today if the neutron lifetime were much smaller than 886s (the actual value of the neutron lifetime)? Select one: O a. Annihilations mean that the universe is left composed entirely of photons and neutrinos O b. There would be no difference to the actual universe c. Only hydrogen atoms would be present today O d. There would be very small amounts of He in the universe today

Inquiry into Physics

8th Edition

ISBN:9781337515863

Author:Ostdiek

Publisher:Ostdiek

Chapter12: Relativity, Particle Physics, And Cosmology

Section: Chapter Questions

Problem 42Q

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Similar questions

Briefly explain what is meant by “particle horizon” and “event horizon” in cosmology. Calculate the physical particle horizon, RH(t), at time t. Assume a flat FRW universe whichis dominated by a fluid that gives rise to scale factor evolution where n is a constant with 0 < n < 1, and a(t0) = a0.
Assume a power law for the scale factor a = Ctn, where C is a constant. (a) For what values of n are the universe accelerating and decelerating? (b) For deceleration, what is the dependence of H on time?
(a) What Hubble constant corresponds to an approximate age of the universe of 1010 y? To get an approximate value, assume the expansion rate is constant and calculate the speed at which two galaxies must move apart to be separated by 1 Mly (present average galactic separation) in a time of 1010 y. (b) Similarly, what Hubble constant corresponding to a universe approximately old?
Supermassive black holes are thought to exist at the center of many galaxies. (a) What is the radius of such an object if it has a mass of 109 Suns? (b) What is this radius in light years?
Considering the reactions in primordial nucleosynthesis only, what would be the impact on the universe today if the neutron lifetime were much smaller than 886s (the actual value of the neutron lifetime)?
Because of the cosmological expansion, a particular emission from a distant galaxy has a wavelength that is 2.00 times the wavelength that emission would have in a laboratory. Assuming that Hubble’s law holds and that we can apply Doppler-shift calculations, what was the distance (ly) to that galaxy when the light was emitted?
Assuming that the Hubble constant is, in fact, constant over the age of the universe, what is the Hubble look-back time (effectively the age of the universe in this case) if the Hubble constant is measured to be 50 km/s/Mpc (Please give your answer in units of billions of years; i.e. 10 billion years should be answered as 10)? Keep in mind that this is not the observed measurement of the Hubble constant (70 km/s/Mpc) and is only a value given for this problem. That said, it is not incredibly different so you should expect your answer to still be on the scale of billions of years.
The Klein-Gordon equation at background level for a scalar field φ is given by (found in image below) where H is the Hubble parameter, V the potential of the scalar field, and V′ = dV/dφ.Assume a flat Friedmann-Robertson-Walker universe, dominated by the scalar field.i) State the conditions for slow-roll inflation. Write down the Friedmann equation and theKlein-Gordon equation valid for slow-roll inflation.ii) For a scalar field potential V =1/2m^2φ^2, where m is the mass of the field, calculate thetime evolution of the field φ in the case of slow-roll inflation.
Use the distance and velocity data tofind the rate of expansion as a function of distance.(b) If you extrapolate back in time, how long ago would all ofthe galaxies have been at approximately the same position?The two parts of this problem give you some idea of how theHubble constant for universal expansion and the time back tothe Big Bang are determined, respectively
The average lifetime of a pi meson in its own frame of reference (i.e., the proper lifetime) is 2.6 x10-8 s. If the meson moves with a speed of 0.93c, what is its mean lifetime (s) as measured by an observer on Earth? What is the average distance (m) it travels before decaying, as measured by an observer on Earth? What distance (m) would it travel if time dilation did not occur?
(a) Calculate The approximate age of the universe from the average value of the Hubble constant, To do this, calculate the time it would take to travel 1 Mly at a constant expansion rate of 20 km/s. (b) If deceleration is taken into account, would the actual age of the universe be greater or less than that found here? Explain.