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Space-Time Curvature and the General Theory of Relativity01:17

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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.
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Symmetry in Maxwell's Equations01:28

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Once the fields have been calculated using Maxwell's four equations, the Lorentz force equation gives the force that the fields exert on a charged particle moving with a certain velocity. The Lorentz force equation combines the force of the electric field and of the magnetic field on the moving charge. Maxwell's equations and the Lorentz force law together encompass all the laws of electricity and magnetism. The symmetry that Maxwell introduced into his mathematical framework may not be...
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James Clerk Maxwell (1831–1879) was one of the significant contributors to physics in the nineteenth century. He is probably best known for having combined existing knowledge of the laws of electricity and the laws of magnetism with his insights to form a complete overarching electromagnetic theory, represented by Maxwell's equations. The four basic laws of electricity and magnetism were discovered experimentally through the work of physicists such as Oersted, Coulomb, Gauss, and...
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The principle of conservation of mass is fundamental in fluid dynamics and is crucial for analyzing flow within fixed control volumes, such as pipes or ducts. This principle states that the total mass within a control volume remains constant unless altered by the inflow or outflow of mass through the control surfaces. This results in a vital relationship for steady, incompressible flow where the mass entering a system equals the mass leaving it.
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Related Experiment Video

Updated: Jan 4, 2026

Setting Limits on Supersymmetry Using Simplified Models
07:46

Setting Limits on Supersymmetry Using Simplified Models

Published on: November 15, 2013

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Hiding the Cosmological Constant.

S Carlip1

  • 1Department of Physics, University of California, Davis, Davis, California 95616, USA.

Physical Review Letters
|November 8, 2019
PubMed
Summary
This summary is machine-generated.

Vacuum fluctuations may generate a large cosmological constant. However, without assuming homogeneity or an arrow of time at the Planck scale, this constant averages to zero macroscopically, creating a "spacetime foam" effect visible only at small scales.

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Last Updated: Jan 4, 2026

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Area of Science:

  • Cosmology
  • Quantum Gravity
  • General Relativity

Background:

  • Standard effective field theory suggests vacuum fluctuations create a large cosmological constant.
  • The cosmological constant's large value presents a significant challenge in modern physics.

Purpose of the Study:

  • To investigate the cosmological constant's behavior without assuming Planck-scale homogeneity or an arrow of time.
  • To explore the implications of general relativistic initial data on small and large scales.

Main Methods:

  • Analysis of general relativistic initial data under relaxed homogeneity and time-arrow assumptions.
  • Examination of spacetime evolution, curvature, expansion, and shear at Planck and macroscopic scales.

Main Results:

  • A large class of initial data exhibit enormous expansions, shears, and curvatures at small scales.
  • These extreme values rapidly average to zero macroscopically.
  • Quantum fluctuations may preserve these Planck-scale properties.

Conclusions:

  • The cosmological constant may be large at the Planck scale but effectively zero at observable scales.
  • This resolves the cosmological constant problem by reconciling theoretical predictions with observations.
  • The findings support a
  • spacetime foam
  • model consistent with Wheeler's ideas.