Crossable Wormholes?

[Music] welcome back to science click today wormholes according to the theory of general relativity our universe is a four-dimensional hyper surface in which move about all objects this is space-time space-time is not entirely rigid it possesses a certain geometry that might be distorted in the presence of mass and energy it can bend it is this curvature which is responsible for gravitation a black hole is an object whose mass is concentrated in a single point which we call the singularity because of their mass black holes distort space-time around them very close to the black hole space-time becomes so distorted that all objects and even light can no longer escape this is the horizon of the black hole a sphere inside which the curvature of space-time is so great that it becomes impossible to escape it to better visualize a black hole we can represent its geometry by doing what is called an embedding in mathematics the embedding will give us a geometric shape which faithfully renders how space is curved around the black hole after the mass we see that space around a black hole behaves essentially like a funnel at a distance it is rather flat its Bend is almost non-existent however the closer we get to the horizon of the black hole the greater the gravitational pull surprisingly at first glance we have the impression that the very structure of the universe contains a hole the existence of this hole might seem strange we might wonder what would happen if a spaceship arrived at its edge does the universe stop at this hole to answer this question it is necessary to understand a certain mathematical subtlety our universe possesses four dimensions three dimensions of space and one dimension of time by representing the geometry of space we overlooked two of these dimensions on one part the horizon of the black hole is supposed to be a sphere but here to be able to represent the space-time we have cancelled out one of the dimensions of space the horizon comes to be a circle furthermore we have only represented the curvature of space not that of time we have deliberately overlooked the temporal dimension of our diagram consequently the diagram is static it represents the curvature of space at one unique moment in time when it falls towards the black hole our spaceship moves forward in time indeed if time did not flow and the spaceship would remain motionless as such when we look at the descent of the spaceship as time progresses it is necessary for our embedding to evolve as well such that it remains representative of the curvature of space-time at each instant when we make our diagram evolve in this way we realize that the hole closes in on itself very quickly once it reaches the horizon of the black hole the spaceship keeps traveling through it and continues its descent towards the central singularity mathematically we can show that regardless of the observer and even for a ray of light this kind of hole in the universe will always close in on itself sufficiently fast for it to be unreachable according to general relativity the structure of space can allow for such a hole but this hole must ultimately close in on itself extremely quickly such that it is impossible to reach it as such the universe does not really possess any holes but from the point of view of our imagination and from that of mathematical elegance this is not very satisfactory even if it closes in on itself very quickly the hole does seem to exist for a brief moment which seems strange we get the impression that there is something missing in our theory that it does not perfectly describe the situation with mathematics it is possible to duplicate the geometry of space inside our equations to make a copy of it only in reverse in this reversed version the copy of the black hole behaves differently instead of not being able to escape from its inside all objects are on the contrary destined to escape from it this is what we call a white hole now that we find ourselves in possession of this copy of space-time we are able to stick it underneath our original hole this mathematical move is admittedly artificial and cannot be readily backed up by any sort of physical observation it is merely a mathematical extension which is motivated by the symmetry of equations we form a structure which is much more satisfactory with the shape of a tube rather than the simple hole it is this type of structure which we call a wormhole if such a structure exists then the wormhole must necessarily connect to portions of space-time together it might connect two independent universes together but it is also likely that it might connect to different parts of one same universe in this way it would form a geometric shortcut between these two regions which light and objects could use to travel quicker from one place to another giving free rein to our imaginations we can quickly start to dream of a future in which spaceships might go through such shortcuts in space-time to travel from galaxy to galaxy however this wormhole which is made up of a black hole in the white hole in which we also call the Alan Rosen bridge cannot be crossed as we have seen previously its structure in the shape of a tube closes in on itself extremely quickly thus strangling any object as adventures inside in this way it is impossible to cross and all that can be done is descend towards the singularity of the black hole fortunately for our curiosity there exist other geometries for wormholes which are mathematically valid under general relativity and whose properties are more advantageous firstly if a black hole rotates on itself or if it possesses an electric charge then it might be possible to cross the wormhole associated to that black hole in this case the central singularity is not a fixed point but a ring which generates rounded a new horizon through which it might be possible to pass having said that this wormhole would only be crossable in one direction it would not be possible to travel the other way through the white hole theoretical physicists have come up with more sophisticated geometries with properties that are more interesting and which go beyond black holes and white holes to allow for true travel through space-time these wormholes are purely mathematical and conceived to obey certain feasibility conditions firstly we want our wormhole to be crossable both ways unlike the einstein-rosen bridge it must be deprived of any sort of horizon so as to make any point crossable one way or the other secondly the wormhole has to be stable in time indeed if it closes in on itself or if it is unstable it would be very risky to travel through it thirdly to be able to cross it smoothly the tube which makes up the wormhole has to be sufficiently wide otherwise it would simply be impossible to fit in it fourthly the time necessary to cross that wormhole must be reasonable a few years for example if the journey takes billions of years the wormhole would be of no great use finally the gravitational forces generated by its geometry must not be too strong so that they do not damage or stretch the structure of the spaceship traveling through the wormhole mathematically there exist such geometries which are accepted by the theory of general relativity one of the easiest examples is the Morris thorne wormhole the Morris Thorne wormhole possesses a number of very interesting properties it has no horizons no singularities and is perfectly stable in time it will not close in on itself while an object goes through it [Music] this type of wormhole is particularly interesting in that it is purely geometric meaning that its structure does not enable it to generate a gravitational pull as such it is possible to stay motionless next to such a wormhole without it either pulling us in or repelling us when we might try to cross it our spaceship will move along a geodesic a straight line within the bend of space-time the geodesic lines of the Morris thorne wormhole are particularly interesting certain trajectories will enter the wormhole go around in circles inside it but end up coming out of the cheap from the same end they entered to go through this wormhole given that it does not generates a gravitational pull to draw things in it is necessary to orient the spaceship precisely towards the center of the hole at first glance just like for a black hole light rays are deviated by this geometry the wormhole acts like a lens which distorts the image of neighboring stars but since light race can also go through we can also manage to observe an image of the entities on the other side of the wormhole thus visualizing the part of the universe with which it links up the Morris Thorne wormhole is particularly elegant and seems to meet all the necessary conditions for the possibility of intergalactic travel however it's not that straightforward its existence relies in fact on it being stable by placing around a sphere of negative energy this negative energy is necessary to counter the tension of space-time which continually forces structures of this type to collapse on themselves as we saw with the einstein-rosen bridge unfortunately as per general relativity we can show that such negative energy is mathematically impossible which means that stable wormholes cannot exist as disappointing as this may seem wormholes are thus impossible from the perspective of general relativity because their existence as stable structures depends on the presence of negative energy over a long period of time which is mathematically impossible this strong principle is called topological censorship theorem it tells us that any wormhole like structure will censor itself automatically or in other words close in on itself for any observer attempting to reach it but these definitive conclusions are only based on general relativity however we know very well that this theory is not perfect it does not take into account certain quantum phenomena which occur at microscopic scales at these scales other theories come into play such as quantum field theory according to this theory which describes particles at a quantum scale vacuums possess a certain energy which is constantly agitated by fluctuations these fluctuations are known as virtual particles and we can liken them to ordinary particles that would appear and disappear extremely quickly all these virtual particles generate a type of residual pressure in space which in certain configurations acts in identical manner to negative energy this is known as the Casimir effect as such even though general relativity seems to reject the possibility of stable wormholes quantum phenomena could bring a solution to the problem certain scientists already imagined parallels between wormholes in the phenomenon of quantum entanglement moreover certain more speculative theories such as string theory for example offer new perspectives to conceptualize the existence of natural wormholes which would have formed just after the Big Bang and which would have gotten stretched after their creation by the expansion of the universe in string theory such wormholes would be stabilized by cosmic strings which have announced they're purely hypothetical objects finally if the existence of wormholes could truly be proven it would bring about the question of time travel indeed the theory of relativity which works not on space but on space-time does not prevent such an object from linking to different instants in time we are still uncertain whether or not it would be possible to travel into the past but wormholes could make it possible having said that for coherence reasons a wormhole would however never be able to take travelers further back in the past than the very moment of its creation wormholes are objects that are fascinating from a mathematical perspective studying them remains very speculative but nonetheless enables us to reinforce our current theories by constantly putting them up to the test and by constantly trying to push back their limits although the possibility of crossable wormholes should not be discarded entirely as for today the only people crossing wormholes are theoretical physicists with equations as their spaceships [Music]

Channel: ScienceClic English

Views: 466,868

Rating: 4.9079375 out of 5

Keywords: wormholes, wormhole, einstein, rosen, general relativity, worm hole, worm holes

Id: bv-2SP7-ZEY

Length: 14min 38sec (878 seconds)

Published: Sat Mar 30 2019