# I Wormhole Travel

#### John Morax

Hi!

I've just read some articles about the fact that wormhole travel would be slower then taking a "regular space time path" between two hypothetical black holes.
This stunned me as I always thought the Einstein - Rosen Bridge would be connecting two distant points in space in a more direct and shorter way. Think about the classic wormhole diagram: we can clearly see the distance through the bridge is way shorter then the curved space time path.
My questions is: Why would wormhole travel take longer? I couldn't find a clear explanation in those articles I read and I am very interested.

Thank you!

#### fresh_42

Mentor
2018 Award
I've just read some articles
Do you have a link? And at best, also to the paper the article was based on?

#### John Morax

I found a few like this one. They say pretty much the same thing without getting to the core of the argument.

Sorry I should have posted this before.

#### fresh_42

Mentor
2018 Award
For the record:
The prospect of traversable wormhole configurations has long been a source of fascination. I will describe the first examples that are consistent in a UV completable theory of gravity, involving no exotic matter. The configuration involves a direct connection between the two ends of the wormhole. I will also discuss its implications for quantum information in gravity, the black hole information paradox, and its relation to quantum teleportation.
APS April Meeting 2019
Volume 64, Number 3
Saturday–Tuesday, April 13–16, 2019; Denver, Colorado

Daniel L. Jafferis (Harvard)

#### George Jones

Staff Emeritus
Gold Member
I've just read some articles about the fact that wormhole travel would be slower then taking a "regular space time path" between two hypothetical black holes.
This stunned me as I always thought the Einstein - Rosen Bridge would be connecting two distant points in space in a more direct and shorter way.

The Einstein-Rosen bridge in classical general relativity is not a traversable wormhole

For the record:

APS April Meeting 2019
Volume 64, Number 3
Saturday–Tuesday, April 13–16, 2019; Denver, Colorado

Daniel L. Jafferis (Harvard)

The abstract from the talk given at the meeting:
The prospect of traversable wormhole configurations has long been a source of fascination. I will describe the first examples that are consistent in a UV completable theory of gravity, involving no exotic matter. The configuration involves a direct connection between the two ends of the wormhole. I will also discuss its implications for quantum information in gravity, the black hole information paradox, and its relation to quantum teleportation.

My first thought while reading this abstract: there is no UV completable theory of gravity, at least not a realistic one that makes predictions.

My second though while reading the abstract: in standard (linear) non-relativistic quantum mechanics, quantum teleportation cannot be used to send information faster than the speed of light, so if this wormhole is related to teleportation, maybe this is the reason that travel through this wormhole is "slow".

Back to my first thought. BTZ black holes are solutions in 2+1 spacetime, 3-dimensional spacetimes that have two spacelike dimensions and one time-like dimension, i.e., one spacelike dimension has been torpedoed in order to make the quantum gravity problem more tractable.

From Steve Carlip's book "Qunatum Gravity in 2+1 Dimensions:
The fundamental physical difference between general relativity in 2+1 and 3+1 dimensions originates in the fact that the curvature tensor in 2+1 dimensions depends linearly on the curvature tensor ... In particular, this means that every solution of the vacuum Einstein equations with $\Lambda = 0$ is flat, and that every solution with a non-vanishing cosmological constant has constant curvature. Physically, a (2+1)-dimensional spacetime has no local degrees of freedom, and there are no gravitational waves. If the spacetime $M$ is topologically trivial, there are, in fact, no gravitational degrees of freedom at all. If $M$ has a nontrivial fundament group, though, we shall see later that a finite number of global degrees of freedom remain, providing the classical starting point for a quantum theory.

In other words, this wormhole is for a toy model of gravity that ditches one spacelike dimension and gravitational degrees of freedom in order to be able to talk about quantum gravity.

Still, this is fascinating stuff.

ArXiv reference (to prelimanry work?):

#### John Morax

Thanks for the reply.
I am not a physicist neither I ever went to Uni for the matter , so it is difficult for me to follow this reasoning through.

You are right in saying that E-R bridges are not traversable, being tiny as they are.
But how about 2 entangled black holes? Wouldn't there be a connection faster then light between them? Maybe through a wormhole?

I still think that those articles are not clearly explaining the reasons behind this "hypothetical travel in an hypothetical traversable E-R bridge" being "slow".

Anyway, I know we are in uncharted territory here. Lots of speculations going on...
I greatly appreciate the time you sir are spending to reply a humble man full of curiosity. Thank you.

#### PeterDonis

Mentor
how about 2 entangled black holes?
We don't have a good quantum theory of gravity so we can't say anything very definite about this; it's at least as speculative as the particular kind of traversable wormhole that is said to be "slow" in the articles you refer to. See further comments below.

I still think that those articles are not clearly explaining the reasons behind this "hypothetical travel in an hypothetical traversable E-R bridge" being "slow".
First, as has already been pointed out, the E-R bridge is not a traversable wormhole. And traversable wormholes are not well described as "traversable E-R bridges". If you are interested in traversable wormholes, it is best to just forget about E-R bridges altogether.

Second, the type of traversable wormhole being described in the articles you link to is just one particular kind. There are other kinds (such as the original Morris-Thorne wormhole first described in the 1980s) through which travel is not "slow" in the sense described. But those other kinds require exotic matter (which is not thought to actually exist, hence could not be used to construct an actual wormhole); the "slow" kind described in the articles you refer to does not, but it does depend on speculative quantum gravity models that have not been experimentally tested (and can't be now or in the foreseeable future).

#### John Morax

Thanks.
It does make a lot of sense what you wrote.

I hope that one day we will understand better what really are the laws ruling the most fascinating things in the known Universe, so to have a clear picture within the correct model.

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