Tuesday, January 31, 2023

The Connection Between Cosmic 'White Holes' And Wormholes Now Makes Sense


                                  Artist's depiction of a Worm hole

Following the history of the "worm hole" - or its origin artifact called "the white hole"-  is an interesting exercise in the history of modern cosmology.  Originally, in the late 70s, "white holes" were conceived of as time reversals of black holes, e.g. by popularizers such as John Gribbin ('White Holes- Cosmic Gushers In the Universe', 1977).

In the diagram below, one of the earliest models ca. 1975, the black and white holes represent equally open ‘rips’ in the fabric of space-time.

 The difference is that in the first matter is sucked in (by powerful gravity) and in the second it’s explosively blown out. The wormhole, meanwhile, represents the shortcut through space time linking the two.  

How did this theory - or more accurately, model - come about? The discovery of quasars in the early 1960s, which shook the astronomical world, became the plausible stepping stone to invoke white holes.  How could one explain an object a million times smaller than a normal galaxy but which generated a million times more energy?  The white hole proposal sought to 'kill 2 birds with one stone':  It would explain the prodigious energy output of quasars and also explain what happened to the matter at a black hole's singularity.  

The white hole, then emerged quite naturally out of the mathematical consideration of black holes. It turns out that for a static (non-rotating) black hole the singularity is linked via a 'bridge' to another point in our universe (as depicted in the sketch above). It is then at the white hole that the mass-energy consumed by the black hole would be expected to emerge, but now in the form of the quasar.

 Unfortunately, the main problem for this neat model is that a static black hole is not very realistic. After all, the star was rotating when it underwent collapse to form a black hole, so it should be rotating (though much faster) afterwards. Hence, rotating black holes are the only kind one would expect.

Hence, rotating black holes are far more plausible than static ones. Could a rotating black hole work in place of the static one?  Maybe, but let's be clear that there are fundamental differences between the two types of singularities. For the static black hole the singularity is a single point but for the rotating case it is ring-shaped.  

Now replace the single point with a ring-shaped singularity and what do we expect?  Well, we then get a rotating wormhole which might lead to a number of different places in our universe, and at differing times. It is this feature which ed numerous sci-fi writers to speculate on the possibility of using these as 'short cuts' for future space travelers. Say to get between different parts of the universe, as depicted in the 2014 science fiction film, 'Interstellar', e.g.

The film was terrific but cleverly skirted several problems, including that there is no sure way for any would-be space jockey to navigate to his destination through a wormhole. You could end up in a far different location to that you desired, or worse a totally different time.  (The movie escaped this by inventing the ploy of a genius scientist devising a mathematical basis and computer to control for unwanted destinations.)

Added to this, if black holes exist in the way general relativity leads us to suspect, it is doubtful they can be used as ‘gates’ to enter wormholes and get to another part of the cosmos. The reason is that the enormous gravitational pull exerted by a black hole would rend asunder any object in its vicinity. A space ship, therefore, would be ripped to shreds long before it could enter a black hole.

Finally, the whole theory of white holes has fallen more and more into disfavor. We now since found - by way of more recent observations-  that quasars could simply be the ejected cores of energetic galaxies. So, the same source that powers exploding galaxies, could also power them without invoking anything exotic like white holes.  

We may need popular sci-fi writers and screen writers to finally 'catch up' and realize that massive white holes as well as rotating wormholes are no longer 'in', astronomically speaking.  They were exotic constructs for the time, but as in all aspects of science astrophysics has moved on based on new evidence. (Still we must acknowledge that Stephen Hawking in 1975 did succeed in proving at the quantum level that primordial black holes are indistinguishable from white holes.)  

But what we have now, thanks to more recent astrophysical findings, is the connection between white holes and worm holes now make sense.

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