Search research articles

ABOUT JoVE

Overview Leadership Blog JoVE Help Center

AUTHORS

Publishing Process Editorial Board Scope & Policies Peer Review FAQ Submit

LIBRARIANS

Testimonials Subscriptions Access Resources Library Advisory Board FAQ

RESEARCH

JoVE Journal Methods Collections JoVE Encyclopedia of Experiments Archive

EDUCATION

JoVE Core JoVE Business JoVE Science Education JoVE Lab Manual Faculty Resource Center Faculty Site

Terms & Conditions of Use

Related Concept Videos

Subatomic Particles

Subatomic Particles

Dalton was only partially correct about the particles that make up matter. All matter is composed of atoms, and atoms are composed of three smaller subatomic particles: protons, neutrons, and electrons. These three particles account for the mass and the charge of an atom.

Nuclear Stability

Nuclear Stability

Protons and neutrons, collectively called nucleons, are packed together tightly in a nucleus. With a radius of about 10−15 meters, a nucleus is quite small compared to the radius of the entire atom, which is about 10−10 meters. Nuclei are extremely dense compared to bulk matter, averaging 1.8 × 1014 grams per cubic centimeter. If the earth’s density were equal to the average nuclear density, the earth’s radius would be only about 200 meters.
To hold positively charged protons together in the...

Orders of Magnitude

Orders of Magnitude

The order of magnitude of a number is the power of 10 that most closely approximates it. Thus, the order of magnitude estimates the scale (or size) of its value. To find the order of magnitude of a number, take the base-10 logarithm of the number and round it to the nearest integer. Then the order of magnitude of the number is simply the resulting power of 10.
The order of magnitude is simply a way of rounding numbers consistently to the nearest power of 10. This makes doing rough mental math...

Newton's Law of Gravitation

Newton's Law of Gravitation

Our everyday observation tells us that all objects close to the Earth naturally tend to fall to the ground. Early philosophers assumed that this downward force was unique to Earth. By the 16th century, Nicolaus Copernicus (1473-1543) put forward the heliocentric theory, which suggested that Earth and other planets orbited the sun, while the Moon orbited the Earth. However, it was Isaac Newton (1642-1727) who linked these two motions together in the 17th century. He reasoned that the force of...

Space-Time Curvature and the General Theory of Relativity

Space-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,...

Estimation of the Physical Quantities

Estimation of the Physical Quantities

On many occasions, physicists, other scientists, and engineers need to make estimates of a particular quantity. These are sometimes referred to as guesstimates, order-of-magnitude approximations, back-of-the-envelope calculations, or Fermi calculations. The physicist Enrico Fermi was famous for his ability to estimate various kinds of data with surprising precision. Estimating does not mean guessing a number or a formula at random. Instead, estimation means using prior experience and sound...

You might also read

Related Articles

Articles linked to this work by shared authors, journal, and citation graph.

Sort by

Same author

Extreme nonequilibrium synthesis of a Ca-Cu-Si clathrate during the Trinity nuclear test.

Proceedings of the National Academy of Sciences of the United States of America·2026

Same author

Effective Delocalization in the One-Dimensional Anderson Model with Stealthy Disorder.

Physical review letters·2026

Same author

Quantifying when hyperuniformity of a many-particle system leads to uniformity across length scales.

Physical review. E·2025

Same author

Dynamical properties of particulate composites derived from ultradense stealthy hyperuniform sphere packings.

Physical review. E·2025

Same author

Quasicrystal synthesis by shock compression.

Communications chemistry·2024

Same author

Stealthy and hyperuniform isotropic photonic band gap structure in 3D.

PNAS nexus·2024

Search research articles

Related Experiment Video

Updated: Jul 16, 2026

Setting Limits on Supersymmetry Using Simplified Models

Setting Limits on Supersymmetry Using Simplified Models

Published on: November 15, 2013

Why the cosmological constant is small and positive.

Paul J Steinhardt¹, Neil Turok

¹Joseph Henry Laboratories, Princeton University, Princeton, NJ 08544, USA. steinh@princeton.edu

Science (New York, N.Y.)

|May 6, 2006

Summary

A cyclic universe model offers a solution to the small cosmological constant problem. This model features a dynamical mechanism that naturally relaxes the vacuum density, explaining the observed small, positive cosmological constant.

Area of Science:

Cosmology
Theoretical Physics

Background:

The cosmological constant problem is a major challenge in modern cosmology.
Conventional Big Bang models struggle to explain the observed small value of the cosmological constant.

Purpose of the Study:

To propose a cyclic universe model that addresses the cosmological constant problem.
To introduce a dynamical mechanism for relaxing vacuum energy contributions.

Main Methods:

Investigating a cyclic cosmological model.
Analyzing the behavior of vacuum density and relaxation times.

Main Results:

A cyclic model naturally incorporates a mechanism for relaxing the cosmological constant.
The relaxation time increases exponentially with decreasing vacuum density.

More Related Videos

Generation and Coherent Control of Pulsed Quantum Frequency Combs

Generation and Coherent Control of Pulsed Quantum Frequency Combs

Published on: June 8, 2018

A Uniaxial Compression Experiment with CO2-Bearing Coal Using a Visualized and Constant-Volume Gas-Solid Coupling Test System

A Uniaxial Compression Experiment with CO₂-Bearing Coal Using a Visualized and Constant-Volume Gas-Solid Coupling Test System

Published on: June 12, 2019

Related Experiment Videos

Last Updated: Jul 16, 2026

Setting Limits on Supersymmetry Using Simplified Models

Setting Limits on Supersymmetry Using Simplified Models

Published on: November 15, 2013

Generation and Coherent Control of Pulsed Quantum Frequency Combs

Generation and Coherent Control of Pulsed Quantum Frequency Combs

Published on: June 8, 2018

A Uniaxial Compression Experiment with CO2-Bearing Coal Using a Visualized and Constant-Volume Gas-Solid Coupling Test System

A Uniaxial Compression Experiment with CO₂-Bearing Coal Using a Visualized and Constant-Volume Gas-Solid Coupling Test System

Published on: June 12, 2019

Conclusions:

The proposed cyclic model explains why the cosmological constant is small and positive today.
Nearly all space spends most of its time in a state with a small cosmological constant.