Related Experiment Video
Updated: Aug 6, 2026
12:14
The Generation of Higher-order Laguerre-Gauss Optical Beams for High-precision Interferometry
Published on: August 12, 2013
New cosmic microwave background constraint to primordial gravitational waves
Tristan L Smith1, Elena Pierpaoli, Marc Kamionkowski
1California Institute of Technology, Mail Code 130-33, Pasadena, 91125, USA.
Physical Review Letters
|August 16, 2006
Summary
Primordial gravitational waves (GWs) impact the cosmic microwave background (CMB) radiation density. Current observations constrain GW amplitude, with future experiments promising even greater sensitivity to these early Universe signals.
Area of Science:
- Cosmology
- Astrophysics
- Gravitational Wave Astronomy
Background:
- Primordial gravitational waves (GWs) influence the Universe's radiation density at cosmic microwave background (CMB) decoupling.
- Their effect on CMB and matter power spectra is similar to massless neutrinos, depending on initial conditions.
Purpose of the Study:
- To constrain the amplitude of primordial gravitational waves using current observational data.
- To assess the potential sensitivity of future CMB experiments to primordial GWs.
Main Methods:
- Analysis of CMB and matter power spectra to infer constraints on GW amplitude.
- Comparison of GW constraints with those from Big Bang Nucleosynthesis (BBN).
Main Results:
- Current observations constrain the GW amplitude (Ωgw h²) to < 8.4 x 10⁻⁶ at 95% confidence for homogeneous initial conditions.
- This constraint extends to lower frequencies (~10⁻¹⁵ Hz) compared to BBN constraints (~10⁻¹⁰ Hz).
Conclusions:
- Observational constraints on primordial GWs are becoming competitive with BBN.
- Future experiments like Planck and CMBPol will significantly improve sensitivity to primordial GWs, probing lower amplitudes.
Related Concept Videos
01:17Space-Time Curvature and the General Theory of Relativity
In 1905, Albert Einstein published his special theory of relativity. According to this theory, no matter in the universe can attain a speed greater than the speed of light in a vacuum, which thus serves as the speed limit of the universe.
This has been verified in many experiments. However, space and time are no longer absolute. Two observers moving relative to one another do not agree on the length of objects or the passage of time. The mechanics of objects based on Newton's laws of motion,...
This has been verified in many experiments. However, space and time are no longer absolute. Two observers moving relative to one another do not agree on the length of objects or the passage of time. The mechanics of objects based on Newton's laws of motion,...
01:10Detection of Black Holes
Although black holes were theoretically postulated in the 1920s, they remained outside the domain of observational astronomy until the 1970s.
Their closest cousins are neutron stars, which are composed almost entirely of neutrons packed against each other, making them extremely dense. A neutron star has the same mass as the Sun but its diameter is only a few kilometers. Therefore, the escape velocity from their surface is close to the speed of light.
Not until the 1960s, when the first neutron...
Their closest cousins are neutron stars, which are composed almost entirely of neutrons packed against each other, making them extremely dense. A neutron star has the same mass as the Sun but its diameter is only a few kilometers. Therefore, the escape velocity from their surface is close to the speed of light.
Not until the 1960s, when the first neutron...
01:17The Principle of Superposition and the Gravitational Field
The principle of superposition applies to gravitational forces of objects that are sufficiently far apart. It states that the net gravitational force on a point object is the vector sum of the gravitational forces on it due to various objects. The principle helps calculate the force by listing the individual forces and then vectorially summing them up. However, it should be noted that the principle of superposition is not always apparent. In the presence of a second force, the first force could...
01:11Atomic Nuclei: Larmor Precession Frequency
The earth's gravitational field produces a 'twisting force' perpendicular to the angular momentum of a spinning mass (such as a spinning top) that causes the mass to 'wobble' around the gravitational field axis in a phenomenon called precession. Similarly, the magnetic moment (μ) of a spinning nucleus precesses due to an external magnetic field directed along the z-axis. The precession of the magnetic moment vector about the magnetic field is called Larmor precession, and the angular frequency...
01:21Schwarzschild Radius and Event Horizon
No object with a finite mass can travel faster than the speed of light in a vacuum. This fact has an interesting consequence in the domain of extremely high gravitational fields.
The minimum speed required to launch a projectile from the surface of an object to which it is gravitationally bound so that it eventually escapes the object’s gravitational field is called the escape velocity. The escape velocity is independent of the mass of the object. Merging the idea of escape velocity with the...
The minimum speed required to launch a projectile from the surface of an object to which it is gravitationally bound so that it eventually escapes the object’s gravitational field is called the escape velocity. The escape velocity is independent of the mass of the object. Merging the idea of escape velocity with the...
01:14Gravitation Between Spherically Symmetric Masses
The gravitational potential energy between two spherically symmetric bodies can be calculated from the masses and the distance between the bodies, assuming that the center of mass is concentrated at the respective centers of the bodies.