Time travel is possible – but only if you have an object with infinite mass

Phys.org ^ | Dec 13, 2018 | Gaurav Khanna

[ETL]

The concept of time travel has always captured the imagination of physicists and laypersons alike. But is it really possible? Of course it is. We're doing it right now, aren't we? We are all traveling into the future one second at a time.

But that was not what you were thinking. Can we travel much further into the future? Absolutely. If we could travel close to the speed of light, or in the proximity of a black hole, time would slow down enabling us to travel arbitrarily far into the future. The really interesting question is whether we can travel back into the past.

I am a physics professor at the University of Massachusetts, Dartmouth, and first heard about the notion of time travel when I was 7, from a 1980 episode of Carl Sagan's classic TV series, "Cosmos." I decided right then that someday, I was going to pursue a deep study of the theory that underlies such creative and remarkable ideas: Einstein's relativity. Twenty years later, I emerged with a Ph.D. in the field and have been an active researcher in the theory ever since.

Now, one of my doctoral students has just published a paper in the journal Classical and Quantum Gravity that describes how to build a time machine using a very simple construction.

Closed time-like curves

Einstein's general theory of relativity allows for the possibility of warping time to such a high degree that it actually folds upon itself, resulting in a time loop. Imagine you're traveling along this loop; that means that at some point, you'd end up at a moment in the past and begin experiencing the same moments since, all over again – a bit like deja vu, except you wouldn't realize it. Such constructs are often referred to as "closed time-like curves" or CTCs in the research literature, and popularly referred to as "time machines." Time machines are a byproduct of effective faster-than-light travel schemes and understanding them can improve our understanding of how the universe works.

Here we see a time loop. Green shows the short way through wormhole. Red shows the long way through normal space. Since the travel time on the green path could be very small compared to the red, a wormhole can allow for the possibility of time travel. Credit: Panzi, CC BY-SA

Over the past few decades well-known physicists like Kip Thorne and Stephen Hawking produced seminal work on models related to time machines.

The general conclusion that has emerged from previous research, including Thorne's and Hawking's, is that nature forbids time loops. This is perhaps best explained in Hawking's "Chronology Protection Conjecture," which essentially says that nature doesn't allow for changes to its past history, thus sparing us from the paradoxes that can emerge if time travel were possible.

Perhaps the most well-known amongst these paradoxes that emerge due to time travel into the past is the so-called "grandfather paradox" in which a traveler goes back into the past and murders his own grandfather. This alters the course of history in a way that a contradiction emerges: The traveler was never born and therefore cannot exist. There have been many movie and novel plots based on the paradoxes that result from time travel – perhaps some of the most popular ones being the "Back to the Future" movies and "Groundhog Day."

Exotic matter

Depending on the details, different physical phenomena may intervene to prevent closed time-like curves from developing in physical systems. The most common is the requirement for a particular type of "exotic" matter that must be present in order for a time loop to exist. Loosely speaking, exotic matter is matter that has negative mass. The problem is negative mass is not known to exist in nature.

An animation shows how Mallary’s time loop works. As the spacecraft enters the time loop, its future self appears as well, and one can trace back the positions of both at every moment afterwards. This animation is from the perspective of an external …more

Caroline Mallary, a doctoral student at the University of Massachusetts Dartmouth has published a new model for a time machine in the journal Classical & Quantum Gravity. This new model does not require any negative mass exotic material and offers a very simple design.

Mallary's model consists of two super long cars – built of material that is not exotic, and have positive mass – parked in parallel. One car moves forward rapidly, leaving the other parked. Mallary was able to show that in such a setup, a time loop can be found in the space between the cars.

So can you build this in your backyard?

If you suspect there is a catch, you are correct. Mallary's model requires that the center of each car has infinite density. That means they contain objects – called singularities – with an infinite density, temperature and pressure. Moreover, unlike singularities that are present in the interior of black holes, which makes them totally inaccessible from the outside, the singularities in Mallary's model are completely bare and observable, and therefore have true physical effects.

Physicists don't expect such peculiar objects to exist in nature either. So, unfortunately a time machine is not going to be available anytime soon. However, this work shows that physicists may have to refine their ideas about why closed time-like curves are forbidden.

Explore further: Stephen Hawking's final book suggests time travel may one day be possible – here's what to make of it

[guido911]

Infinite Mass? So Rosie O’Donnell and Hillary Clinton can time travel? “Goodnight everyone, tip your waitresses and bartenders. And order the soup.”

[dartuser]

There's a reason only light travels at the speed of light.

Our bodies would radiate into electromagnetic energy like we were an antenna. Had a physics professor outline the equations in answer to this question about 40 years ago ... but after 40 years I have forgotten his development.

[blueunicorn6]

I’ll have some soup.

[RedMonqey]

Infinite mass?

Michael Moore is a “time lord” aka Doctor Who(dat)?

[blueunicorn6]

I’ll have some soup.

[blueunicorn6]

Give me some crackers the next time I come by.

[blueunicorn6]

What am I doing with this spoon?

[Red Badger]

Time travel is impossible, if for no other reason than everything in the universe is MOVING.

Let’s say that you actually have a working ‘Time Machine’.

You step in, turn it on and go back or forward in time to some point.

You exit the time machine and find that you are in empty space, far from the earth or even the solar system or possibly the entire galaxy. You immediately die from lack of oxygen and freeze solid as rock within a few minutes.

Because the earth and the sun and the solar system and the galaxy are moving constantly, but you did not, you just traversed TIME and not SPACE.....................

[faithhopecharity]

an object with infinite mass?

1. my last date
2. my weight loss doctor
3. SorozNazi’s bank account (and Mein Kamph book library)
4. Moslem terrorists’ weapons arsenal
5. Mueller’s “investigation” crap
6. Pelousy/Gore/FakeInjunSquaw/Obama/Kasick/Flake lies
7. ?

[ETL]

Relativistic effects aside, as I understand it, if time travel requires an object of infinite mass...

I actually haven't had time to read the article yet. Posted then ran off to eat dinner. But time travel, at least to the future, doesn't require infinite mass. I can't imagine what they mean by that. Will read now and see. And, as I mentioned at the top, it happens everyday, all around us, to an almost imperceptible degree (only high accuracy atomic clocks can detect it).

[KarlInOhio]

All the inventors of time machines would be fighting on the doorstep of the US Patent Office on the day it opened to get patent #1. First to file would be the rule because no one can sort out first to invent when dealing with a time machine.

[Songcraft]

"I'm going back to when I was skinny, then I'm staying there."

[blueunicorn6]

Aha!

But I went to the 9th Circuit Court and they just overturned all the laws of physics.

Just you try and get around those black robed magicians.

[Lonesome in Massachussets]

You can only remember the past, not the future.

Entropy determines the arrow of time. Watch someone making the opening shot in a game of pool, breaking up the original triangle. No law of physics is violated by running the tape backwards, except that going backwards, entropy decreases and you can tell immediately that the tape is running backwards.

Same thing if you watch a plane crash. You can immediately recognize when the tape is going backwards.

[blueunicorn6]

I’ve given that waitress like three hundred bucks in tips now.

[Getready]

Quantum and new physics mean...”we dont know anything very well.” Publish all this hogwash on the back of theoretical constructs...infinite mass...(can never be achieved by definition...there is always one size bigger}....shut up and supersize my fries.

[KarlInOhio]

You exit the time machine and find that you are in empty space, far from the earth or even the solar system or possibly the entire galaxy. You immediately die from lack of oxygen and freeze solid as rock within a few minutes.

And that's why you need the "And Relative Dimension In Space" part of the TARDIS.

[ETL]

Hafele–Keating experiment

The Hafele–Keating experiment was a test of the theory of relativity.

In October 1971, Joseph C. Hafele, a physicist, and Richard E. Keating, an astronomer, took four cesium-beam atomic clocks aboard commercial airliners.

They flew twice around the world, first eastward, then westward, and compared the clocks against others that remained at the United States Naval Observatory.

When reunited, the three sets of clocks were found to disagree with one another, and their differences were consistent with the predictions of special and general relativity.

Kinematic time dilation

According to special relativity, the rate of a clock is greatest according to an observer who is at rest with respect to the clock.

In a frame of reference in which the clock is not at rest, the clock runs more slowly, as expressed by the Lorentz factor.

This effect, called time dilation, has been confirmed in many tests of special relativity, such as the Ives–Stilwell experiment and experimental testing of time dilation.[1]

Considering the Hafele–Keating experiment in a frame of reference at rest with respect to the center of the earth, a clock aboard the plane moving eastward, in the direction of the Earth’s rotation, had a greater velocity (resulting in a relative time loss) than one that remained on the ground, while a clock aboard the plane moving westward, against the Earth’s rotation, had a lower velocity than one on the ground.[2]

Gravitational time dilation

General relativity predicts an additional effect, in which an increase in gravitational potential due to altitude speeds the clocks up.

That is, clocks at higher altitude tick faster than clocks on Earth’s surface.

This effect has been confirmed in many tests of general relativity, such as the Pound–Rebka experiment and Gravity Probe A.

In the Hafele–Keating experiment, there was a slight increase in gravitational potential due to altitude that tended to speed the clocks back up.

Since the aircraft flew at roughly the same altitude in both directions, this effect was approximately the same for the two planes, but nevertheless it caused a difference in comparison to the clocks on the ground.[2]

https://en.wikipedia.org/wiki/Hafele%E2%80%93Keating_experiment

[kaehurowing]

Supersize me!

[glennaro]

When I was very young my mom took us to Holy Thursday high mass. The experience opened my eyes to many fine things ... including the concept of “infinite”.