7.4 Galaxy Travel | Summary and Q&A

TL;DR

Alice, traveling at nearly the speed of light, would observe blueshifted starlight as X-rays and the cosmic microwave background as ultraviolet light during her journey towards the center of the galaxy.

Key Insights

• ⚡ Alice, traveling at high velocity, would observe blueshifted starlight as X-rays and the cosmic microwave background as ultraviolet light.
• 🏚️ The cosmic microwave background is a relic of the universe 380,000 years after the Big Bang, with a temperature of 2.7 Kelvin.
• 💁 Fluctuations in the energy density of the cosmic microwave background at that time serve as the basis for the formation of galaxies and galaxy clusters.
• ❓ The cosmic microwave background has a spectrum that corresponds to its temperature.
• 🙂 The likelihood of light interacting with matter decreased as the universe expanded, leading to the current appearance of the cosmic microwave background.
• ❎ The cosmic microwave background contains about 400 microwave photons per square cubic centimeter.
• 🤩 The observed spectrum of the cosmic microwave background can be correlated with the presence of stars, galaxies, and galaxy clusters today.

Transcript

MARKUS KLUTE: Welcome back to 8.20, Special Relativity. In this section, we're going to build on-- we just learned about the relativistic Doppler effect and redshift. So we take on traveling through the galaxy from here, from Earth, towards the center of the galaxy. The situation is as follows. We have Bob, who's stationary on our planet, Earth, an... Read More

Questions & Answers

Q: What will Alice see while looking out of the windows of the spacecraft during her journey towards the center of the galaxy?

Alice will observe blueshifted starlight as X-rays and the cosmic microwave background as ultraviolet light due to her velocity, which will make the wavelengths appear shorter.

Q: How long does it take for Alice to accelerate from 0 to her velocity with an acceleration of 10 meters per second squared?

To calculate the time it takes for Alice to accelerate, the specific values of her spacecraft's acceleration and final velocity need to be provided. However, with an acceleration of 10 meters per second squared, she will reach her velocity in a finite amount of time.

Q: What is the temperature of the cosmic microwave background?

The temperature of the cosmic microwave background is approximately 2.7 Kelvin, which corresponds to the spectrum of photons emitted by it.

Q: How do fluctuations in the energy density 380,000 years after the Big Bang relate to the formation of galaxies and galaxy clusters today?

The fluctuations in energy density observed 380,000 years after the Big Bang served as seeds for the formation of galaxies and galaxy clusters as they correlate to the presence of stars and galaxies in the present.

Summary & Key Takeaways

• Bob and Alice are on Earth, and Alice travels towards the center of the galaxy in a spacecraft moving at 0.99999998 times the speed of light.

• In Bob's frame of reference, the journey takes 30,000 years, but for Alice, it only takes two years.

• Alice will observe blueshifted starlight as X-rays and the cosmic microwave background as ultraviolet light due to her high velocity.