A wormhole or Einstein–Rosen bridge is a hypothetical topological feature that would fundamentally be a shortcut connecting two separate points in spacetime. A wormhole, in theory, might be able to connect extremely far distances such as a billion light years or more, short distances such as a few feet, different universes, and different points in time. A wormhole is much like a tunnel with two ends, each at separate points in spacetime. For a simplified notion of a wormhole, space can be visualized as a two-dimensional (2D) surface. In this case, a wormhole would appear as a hole in that surface, lead into a 3D tube (the inside surface of a cylinder), then re-emerge at another location on the 2D surface with a hole similar to the entrance. An actual wormhole would be analogous to this, but with the spatial dimensions raised by one. For example, instead of circular holes on a 2D plane, the entry and exit points could be visualized as spheres in 3D space. Read more

Wormholes in the News ...

Physicists Simulate Sending Particles of Light Into the Past, Strengthening the Case that Time Travel Is Possible   EMN - July 14, 2016

The study of closed timelike curves (CTC’s) provides valuable insight into particles that can loop back on themselves, breaking free of linear time.

Have physicist found the recipe for wormholes   Daily Mail - April 26, 2016

Is the universe littered with wormholes? Supermassive black holes laced with dark matter could produce 'tunnels' in space. Dark matter is one of the most elusive components of our universe, with scientists trying to find physical evidence of it to match our mathematical models of space. While we have been so far unable to see it or measure it directly, physicists believe the enigmatic material fills in the gaps in the universe, while matter makes up the 'stuff', like planets and stars. But a new paper has suggested that adding a sprinkling of dark matter to a supermassive black hole could result in one of the strangest objects in the universe - a wormhole.

Wormhole Created in Lab Makes Invisible Magnetic Field   Live Science - August 20, 2015

Ripped from the pages of a sci-fi novel, physicists have crafted a wormhole that tunnels a magnetic field through space. This device can transmit the magnetic field from one point in space to another point, through a path that is magnetically invisible. From a magnetic point of view, this device acts like a wormhole, as if the magnetic field was transferred through an extra special dimension. The idea of a wormhole comes from Albert Einstein's theories. In 1935, Einstein and colleague Nathan Rosen realized that the general theory of relativity allowed for the existence of bridges that could link two different points in space-time. Theoretically these Einstein-Rosen bridges, or wormholes, could allow something to tunnel instantly between great distances (though the tunnels in this theory are extremely tiny, so ordinarily wouldn't fit a space traveler). So far, no one has found evidence that space-time wormholes actually exist.

Wormhole Is Best Bet for Time Machine, Astrophysicist Says   Live Science - August 26, 2013

The concept of a time machine typically conjures up images of an implausible plot device used in a few too many science-fiction storylines. But according to Albert Einstein's general theory of relativity, which explains how gravity operates in the universe, real-life time travel isn't just a vague fantasy. The concept of a time machine typically conjures up images of an implausible plot device used in a few too many science-fiction storylines.

But according to Albert Einstein's general theory of relativity, which explains how gravity operates in the universe, real-life time travel isn't just a vague fantasy. Traveling forward in time is an uncontroversial possibility, according to Einstein's theory. In fact, physicists have been able to send tiny particles called muons, which are similar to electrons, forward in time by manipulating the gravity around them. That's not to say the technology for sending humans 100 years into the future will be available anytime soon, though. Time travel to the past, however, is even less understood. Still, astrophysicist Eric W. Davis argues that it's possible. All you need, he says, is a wormhole, which is a theoretical passageway through space-time that is predicted by relativity.

Our universe at home within a larger universe? So suggests wormhole research   PhysOrg - April 7, 2010

In physics and fiction, a wormhole is a hypothetical topological feature of spacetime that would be, fundamentally, a "shortcut" through spacetime. Although they are very popular in science fiction, there is no actual evidence that they exist. For a simple visual explanation of a wormhole, consider spacetime visualized as a two-dimensional (2-D) surface (see illustration, right). If this surface is "folded" along a (non-existent) third dimension, it allows one to picture a wormhole "bridge". A wormhole is, in theory, much like a tunnel with two ends each in separate points in space-time.

There is no observational evidence for wormholes, and, although wormholes are valid solutions in general relativity, this is only true if exotic matter can be used to stabilize them. Even if the wormhole is stabilized, the slightest fluctuation in space would collapse it. If such exotic matter (that is, matter with negative mass) does not exist, all wormhole-containing solutions to Einstein's field equations are vacuum solutions, which require an impossible vacuum, free of all matter and energy. There is no evidence or experimental suggestion that wormholes do exist, except as predictions of certain (exotic) physical models. Wormholes allowed by current physical theories might arise spontaneously, but would vanish nearly instantaneously, and would likely be undetectable.

White Holes

In general relativity, a white hole is a hypothetical region of spacetime which cannot be entered from the outside, although matter and light can escape from it. In this sense, it is the reverse of a black hole, which can only be entered from the outside and from which matter and light cannot escape. White holes appear in the theory of eternal black holes. In addition to a black hole region in the future, such a solution of the Einstein field equations has a white hole region in its past. However, this region does not exist for black holes that have formed through gravitational collapse, nor are there any known physical processes through which a white hole could be formed. No white hole has ever been observed. Also, the laws of thermodynamics say that the net entropy in the universe can either increase or remain constant. This rule is violated by white holes, as they tend to decrease entropy.

Like black holes, white holes have properties like mass, charge, and angular momentum. They attract matter like any other mass, but objects falling towards a white hole would never actually reach the white hole's event horizon (though in the case of the maximally extended Schwarzschild solution, discussed below, the white hole event horizon in the past becomes a black hole event horizon in the future, so any object falling towards it will eventually reach the black hole horizon). Imagine a gravitational field, without a surface. Acceleration due to gravity is the greatest on the surface of any body. But since black holes lack a surface, acceleration due to gravity increases exponentially, but never reaches a final value as there is no considered surface in a singularity.

In quantum mechanics, the black hole emits Hawking radiation and so can come to thermal equilibrium with a gas of radiation. Because a thermal-equilibrium state is time-reversal-invariant, Stephen Hawking argued that the time reverse of a black hole in thermal equilibrium is again a black hole in thermal equilibrium. This may imply that black holes and white holes are the same object. The Hawking radiation from an ordinary black hole is then identified with the white-hole emission. Hawking's semi-classical argument is reproduced in a quantum mechanical AdS/CFT treatment, where a black hole in anti-de Sitter space is described by a thermal gas in a gauge theory, whose time reversal is the same as itself. Read more