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### Benefits and Flaws of Loop Quantum Gravity

As with string theory, loop quantum gravity is passionately embraced by some physicists and dismissed by others. The physicists who study it believe that the predictions [more…]

### String Theory: Phantom Energy and Rogue Universes

In string theory, the assumption is that the separate, parallel universes don’t normally interact with each other, but some approaches over the years have called this into question. One of the most recent [more…]

### String Theory: Parallel Universes and the Multiverse

In string theory, the *multiverse* is a theory in which our universe is not the only one; many universes exist parallel to each other. These distinct universes within the multiverse theory are called [more…]

### String Theory: Level 1 Parallel Universes

In string theory, the idea of Level 1 parallel universes basically says that space is so big that the rules of probability imply that surely, somewhere else out there, are other planets exactly like Earth [more…]

### String Theory: Plurality of Worlds in Early Astronomy

Before string theory was a theory, early astronomy provided some support for the existence of a *plurality of worlds,* a view that was so controversial that it contributed to at least one man’s death. These [more…]

### String Theory: Level 2 Parallel Universes

In the string theory of a Level 2 parallel universe, regions of space are continuing to undergo an inflation phase. Because of the continuing inflationary phase in these universes, space between us and [more…]

### String Theory: Chaotic Inflation and Eternal Inflation

The theories of eternal inflation and chaotic inflation in string theory can be quite confusing. Most people, even physicists, use them fairly interchangeably. This is an excellent example of how concepts [more…]

### String Theory: Level 3 Parallel Universes

Of the four types of universes, Level 3 parallel universes have the least to do with string theory directly. A Level 3 parallel universe is a consequence of the many worlds interpretation [more…]

### String Theory: Alternate History in Many Worlds Interpretation

Level 3 universes have the least to do with string theory, but of all the types of parallel universes, Level 3 universes have most captured the imagination of popular culture, spawning their own genre [more…]

### String Theory: Level 4 Parallel Universes

In string theory, a Level 4 parallel universe is the strangest place (and most controversial prediction) of all, because it would follow fundamentally different mathematical laws of nature than our universe [more…]

### String Theory: Accessing Other Universes

Is there any way to reach the four types of parallel universes in string theory? Realistically, the answer is probably “No,” but that’s not the most interesting option. Theoretically, there are ways that [more…]

### String Theory: Travel between Parallel Universes with Wormholes

Even before string theory, the idea existed that the geometry of the universe would allow for shorter paths between points. In fiction, this can be seen in stories such as Lewis Carroll’s [more…]

### String Theory: Access Parallel Universes with Quantum Tunneling

In string theory, one process of getting from one universe to another would be to use the property of *quantum tunneling,*which is where a particle is allowed to “jump” from one location to another across [more…]

### How to Calculate Power Based on Work and Time

Sometimes, it isn’t just the amount of work you do but the rate at which you do work that’s important. In physics, the concept of power gives you an idea of how much work you can expect in a certain amount [more…]

### Relating Impulse and Momentum through the Impulse-Momentum Theorem

In physics, you can connect the impulse you give to an object — like striking a pool ball with a cue — with the object’s change in momentum; all you need is a little algebra and a process called the [more…]

### How to Calculate Force from Impulse and Momentum

In physics, you can use the impulse-momentum theorem to calculate force based on impulse and momentum. For example, you can relate the impulse with which you hit an object to its consequent change in momentum [more…]

### How the Principle of Conservation of Momentum Works

In physics, the *principle of conservation of momentum*states that when you have an isolated system with no external forces, the initial total momentum of objects before a collision equals the final total [more…]

### How to Find the Velocity of Two Objects after Collision

You can use the principle of conservation of momentum to measure characteristics of motion such as velocity. Say, for example, that you’re out on a physics expedition and you happen to pass by a frozen [more…]

### How to Determine Whether a Collision Is Elastic or Inelastic

In physics, collisions can be defined as either elastic or inelastic. When bodies collide in the real world, they sometimes squash and deform to some degree. The energy to perform the deformation comes [more…]

### How to Calculate Velocities of Two Objects with Different Masses after an Elastic Collision

When a collision between two objects is elastic, kinetic energy is conserved. In physics, the most basic way to look at elastic collisions is to examine how the collisions work along a straight line. If [more…]

### How to Change Equations from Linear Motion to Rotational Motion

In physics, when you go from linear motion to rotational motion, you need to change the equations that you use to calculate your results. Here are the angular equivalents [more…]

### Calculating Tangential Velocity on a Curve

When an object moves in a circle, if you know the magnitude of the angular velocity, then you can use physics to calculate the tangential velocity of the object on the curve. [more…]

### How to Calculate Torque Perpendicular to Where Force Is Applied

In physics, how much torque you exert on an object depends on two things: the force you exert, *F*; and the *lever arm.* Also called the *moment**
**arm*, the lever arm is the perpendicular distance from the pivot [more…]

### How to Convert Linear Force to Angular Torque

Using physics, you can convert linear force to angular torque. For example, say that you’re whirling a ball in a circle on the end of a string, as shown in the figure. You apply a tangential force [more…]

### How to Calculate the Momentum of Inertia for Different Shapes and Solids

In physics, when you calculate an object’s moment of inertia, you need to consider not only the mass of the object but also how the mass is distributed. For example, if two disks have the same mass but [more…]