Cosmic Microwave Background

The slight variances in the temperature of the cosmic microwave background radiation as seen by the European Space Agency's Planck spacecraft. Leftover light from the Big Bang stretched into microwave wavelengths over cosmic history. (Image Credit: ESA/Planck)

The cosmic microwave background (CMB) is the oldest detectable light in the universe. This light fills the sky as a faint glow in the radio portion of the electromagnetic spectrum, peaking in the microwave frequency range. The CMB is thus invisible to the human eye, but scientists can study it using instruments sensitive to microwaves. The CMB is often referred to as the relic radiation, or afterglow, of the Big Bang, the event that began the universe 13.8 billion years ago. The CMB itself was generated about 378,000 years after the Big Bang during an epoch called "recombination." After the cosmos had cooled from its initially infernal temperatures to about 5,000 degrees Fahrenheit, the elementary particles of protons and electrons that were forged in the Big Bang joined to form hydrogen atoms. This recombination released photons, or particles of light, that now stream toward us from every direction. Analysis of the CMB has enabled researchers to estimate the universe's age as well as its composition of 68 percent dark energy, 27 percent dark matter and 5 percent "normal," everyday matter. Furthermore, the temperature variations and other detailed properties of the CMB speak to the universe's earliest development, including the possibility that it underwent a rapid period of expansion known as inflation.

Ripple Effect: Gravitational Waves Begin to Reveal a Hidden Universe

A visualization of a supercomputer simulation of merging black holes sending out gravitational waves. (Credit: NASA/C. Henze)
Feb 11, 2016

Three principal researchers at the Laser Interferometer Gravitational-Wave Observatory (LIGO)—Nergis Mavalvala, Rainer Weiss and Matthew Evans—reflect on the epic discovery of gravitational waves and how it will transform the way we see the cosmos.

Spotlight Live: Looking Back in Time - Oldest Light in Existence Offers Insight into the Universe (Transcript)

Cosmic Microwave Background
Mar 09, 2015

The most accepted idea for how the early universe behaved, cosmic inflation, remains more an abstraction than full-fledged theory. During a live Google Hangout, three preeminent scientists considered the evidence for and against this contentious concept.

Planck Space Telescope Brings Early Universe into Focus

Planck space telescope
Feb 16, 2015

The latest data release from the Planck space telescope offers insight into everything from the fabric of space to dark matter – and may even have a shot at detecting gravitational waves, says Kavli Institute for Cosmology Director George Efstathiou.

Spotlight Live: Looking Back in Time - Oldest Light in Existence Offers Insight into the Universe

Feb 16, 2015

ON FEBRUARY 18, 2015 three preeminent scientists came together to discuss the latest results, what they mean for the theory of inflation, and what we can expect to learn about the very early universe in the coming decade.

2014 Kavli Prize in Astrophysics: A Discussion with Alan Guth, Andrei Linde and Alexei Starobinsky

Sep 06, 2014

The winners of the 2014 Kavli Prize in Astrophysics – Alan Guth, Andrei Linde and Alexei Starobinsky – discuss their development of the theory of inflation and reflect on how it has changed our view of the universe.

Instantaneous Cosmic Growth: Have We Found the Smoking Gun?

Gravitational waves
May 19, 2014

Scientists have announced we may now have the first “smoking gun” evidence that the universe expanded with unmatchable speed in its earliest moments. Three theoretical physics consider the implications of this stunning development.

Spotlight Live: Secrets of the Universe’s First Light (Transcript)

Apr 29, 2014

The Kavli Foundation hosted a Google Hangout so that four preeminent astrophysicists could discuss this question. Read a modified transcript of the discussion.

Spotlight Live: Secrets of the Universe’s First Light

Spotlight Live: Secrets of the Universe’s First Light
Apr 14, 2014

John Carlstrom, Walter Ogburn, Michael Turner and Abigail Vieregg talk about the first hard evidence that the universe swelled from microscopic to cosmic size in less than the blink of an eye.

KIPAC Special Colloquium: 'Swirls from the Big Bang'

Mar 18, 2014

SLAC and Stanford scientists, many from the Kavli Institute for Particle Astrophysics and Cosmology (KIPAC), are at the center of the exciting new results of cosmic inflation and will be holding a special colloquium to celebrate on Wednesday, March 19 from 3:00-5:30pm PDT on the SLAC campus.

A Conversation with George Efstathiou

George Efstathiou
Jan 28, 2014

In a recent interview, KICC Director George Efstathiou reflected on his latest work and the first sparks that fired his imagination about cosmology.


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