Chapters:
0:00 – Einstein’s predictions
1:51 – How wormholes are predicted
3:39 – Kip Thorne time travel thought experiment
6:55 – Why don’t we see time travelers now?
7:25 – Could black holes be wormholes?
8:35 – Could we create wormholes?
9:15 – What is negative mass?
10:19 – Proposals to create wormholes
11:15 – Why the NOW is precious
References:
Maldacena and Milekhin paper: https://arxiv.org/pdf/2008.06618.pdf
Detecting wormholes in centers of galaxies: https://arxiv.org/pdf/2008.09411.pdf
Making wormholes using black holes: https://arxiv.org/abs/1908.03273
How to build a wormhole with cosmic strings: https://t.ly/TWS3
Summary:
Traveling forward in time is not a problem. You’re doing that now. Can we travel backward in time? There is a theoretically possible way to do it using wormholes.
One solution to general relativity predicts an Einstein Rosen bridge, which is a type of wormhole. If this is real, they could also allow us to travel back in time.
Einstein’s field equations are nothing but a tool to understand how matter affects the curvature of spacetime and how spacetime affects matter. So we can imagine almost any creative spacetime curvature that results in a worm hole, and then by solving the field equations figure out how the matter in this spacetime must be configured to obtain that desired curvature.
One solution can form a spacetime curvature that is like a tunnel or shortcut between two points in space. These points can in principle be very far apart in space, or they can also be different points far apart in time. By traversing this wormhole, you can effectively travel faster than the speed of light.
Caltech physicist Kip Thorne came up with a thought experiment to achieve this: Imagine in the year 2200, we create a stable and traversable wormhole in a lab on earth. We then take one end of the wormhole and place it on a spaceship that can travel nearly at the speed of light. The other end of the wormhole stays in the lab on earth.
If the spaceship travels at 99.5% the speed of light for a year, according to special relativity, the clock on the ship containing the astronaut and the wormhole will run about 10x slower compared to the clock on earth. This is time dilation. So by the time the astronaut returns to earth, 10 years will have gone by for the scientist in the lab, but only one year will have gone by for the astronaut and the wormhole on the ship.
The year would be 2210, but biologically the astronaut is only 1 year older. But, because the wormhole in the lab 10 years earlier would have its clock synchronized with the wormhole on the spaceship, even though the astronaut is physically in the year 2210, he could step into the wormhole and land in the lab in the year 2201 because only one year would have gone by for the two synchronized wormholes. He would be able to travel back in time.
In addition, the scientist in the lab in the year 2201 would be able to step into her wormhole and land 9 years into the future. She could travel forward in time. But by the same token, the same scientist in the lab in the year 2210 would be able to step into the astronaut’s wormhole and travel back in time to 2201 as well.
If the spaceship could travel even faster, then the bigger time dilation could allow it to end up hundreds or thousands of years into the future, allowing future humans to go back in time to point where the wormholes were first created, and for humans in the past to go to the future.
Note that you would not be able to travel further back in time than the point when the wormhole was first created. So this may answer the question, if time travel is possible, why don’t we see time travelers all over the place? The answer could be that wormhole has not been created yet.
How realistic is this wormhole concept? No wormholes have been observed. But in a new paper, Russian astronomers suggest that black holes at the centers of some bright galaxies, may in fact be wormholes.
Could we create a wormhole in the lab? One problem is that when you create a wormhole, the high gravity near the center, where the tunnel connects the two mouths causes it to collapse as soon as anything enters it. It requires exotic matter with negative mass or negative energy to hold it open. Negative matter is not known to exist, but negative energy may have been observed in the Casimir effect.
#timetravel
#wormholes
Other scientists have also proposed creating wormholes by connecting two oppositely charged black holes with cosmic strings to hold their mouths open.
