Physics

Expanding universe may render time travel impossible

Expanding universe may render ...
Professor Richard Muller has put forward a theory that the progression of time is a direct result of the expansion of space
Professor Richard Muller has put forward a theory that the progression of time is a direct result of the expansion of space
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Professor Richard Muller has put forward a theory that the progression of time is a direct result of the expansion of space
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Professor Richard Muller has put forward a theory that the progression of time is a direct result of the expansion of space

In day-to-day human experience, the march of time is constant. Outside the adventures of Marty McFly or Bill and Ted, most people wouldn't normally wonder how time works, but the question of why it moves forwards, has long been on the minds of physicists and philosophers. Now, a professor at UC Berkeley has a new theory: as the universe expands, it drives the expansion of time, which creates a constant series of new "now" moments.

The idea of space and time being intrinsically linked forms the basis of Professor Richard Muller's new theory. Since the moment of the Big Bang approximately 13.8 billion years ago, the universe has been constantly expanding. This doesn't mean that objects in space are drifting apart, but rather, the fabric of spacetime itself, in which objects are embedded, is expanding. Muller's idea is that as new space is created, so is new time, and this constant expansion is what we experience as the progression of time.

"Every moment, the universe gets a little bigger, and there is a little more time, and it is this leading edge of time that we refer to as 'now'," says Muller. "The future does not yet exist … it is being created. 'Now' is at the boundary, the shock front, the new time that is coming from nothing, the leading edge of time."

That's bad news for time travel hopefuls. In practical terms, Muller says that we couldn't travel into the future (except at our current rate of one second per second) because it simply doesn't exist yet, and going backwards would require an associated decrease in the amount of space – it is possible for the amount of space in the universe to decrease due to cataclysmic cosmic events like a black hole disappearing, but only on an immeasurably small scale.

Accepted thinking for the one-way "arrow of time" goes back to Arthur Eddington, who worked closely with Einstein. He suggested in 1927 that time flows in the direction of increasing disorder, or entropy. But Muller argues that human activity is actually decreasing entropy on a local scale, and yet time continues to march forward.

"The idea that the arrow of time is set by entropy does not make any predictions, it is simply a statement of a correlation," says Muller. "And to claim it is causation makes no sense."

Muller believes that in future, his theory could be tested with LIGO, the observatory that detected gravitational waves for the first time back in February. These waves were caused by two black holes merging into one. In doing so, they created new space and, according to Muller's calculations, the event should also have produced about one millisecond of new time. If LIGO observes another event, occurring at around a third of the distance of the previous one, the discovery of a potential one-millisecond delay could support his theory.

So what does the idea mean for us? Not a lot, in practical terms, since the observable effects are likely to be so tiny that only instruments like LIGO could detect them.

"I think my theory is going to have an impact on calculations of the very early universe," says Muller. "I don't see any way that it affects our everyday lives. But it is fascinating."

Muller has just published a book on the theory, titled Now: The Physics of Time. He explains the idea in the video below.

Source: UC Berkeley

Why does time advance?: Richard Muller's new theory

Video by Stephen McNally, courtesy of UC Berkeley under a CC BY 3.0 licence

23 comments
FelixAtkinson
This makes no sense. How can time be created "all the time"? To visualize space expanding we can imagine an animation of a chart axis growing and the notches on it getting further apart OVER TIME. We cannot imagine TIME expanding because the concept of EXPANDING means getting bigger OVER TIME. i.e. an object that is bigger at one point in time than at another. How can TIME be bigger at one point IN TIME than another? Time does not exist IN TIME.
olavn
Each space dimension has expansion in both directions, so shouldn't this also happen for the time dimension? What could be happening in the newly created other end of time? An alternate universe? Does it go along with us as antimatter or dark matter?
GaneshSubramaniam
Makes sense. Time is not 'tangible' - if we accept the concept of 'spacetime' continuum, then time too, is stretching along with space. We talk about the 'past' only because we have 'memory' but what we have is only the 'present' through which we are constantly moving towards the unknown future - one second per second - by our time. We cannot measure time. We have designed clocks to measure the numerical order of material change (frequency, speed) that we observe in space, which is a fundamental entity. The concept of time is exclusively 'human' and our concept of 'time' is only valid for the planet Earth, our home. Our clocks are useless even on the Moon.
Augure
Time-travel has never been possible, because all time is unfolding at the same instants. By that I mean the particles that make-up your body and the universe co-exists at all times, it's just your consciousness that can only perceive one instant. Saying you can travel in time, would mean displacing particles from one instant to a previous one, which is a quantum physics paradox, OR having your consciousness experience a previous instant but then what would that even mean?
MikeHädrich
Overall this is not good news. Find a way out.
Bob
We may not be able to go back in time but we can look back in time with astronomical observations. This brings up other questions. If the universe is expanding, is the speed of light the same if traveling toward the center of expansion or away from it? Has this been distorted by gravitational effects? If so, the 13.8 billion year estimate for the big bang may be totally in error. I have always thought that the age of the universe is closer to 50-100 billion years. This would explain the expansion and many generations of now cold stars which would now make up 90% of the mass of the universe rather than the dark matter and dark energy theories they are using to prop up their original theories. But then, that's my theory.
fb36
"The idea that the arrow of time is set by entropy does not make any predictions, it is simply a statement of a correlation," says Muller. "And to claim it is causation makes no sense." That I agree completely. I think if it was true, speed of local times would vary greatly everywhere. There would be past here and future there all around. But the rest I don't agree. Special Relativity makes clear "now" is relative and past and future coexist.
VincentWolf
The only thing we have to defeat time is immortality. Not there yet.
mscottveach
I don't understand what this means for time dilation. If I was to travel at the near the speed of light around the Earth for a few years then when I land much longer than a few years will have passed for Earth. Either I'm experiencing time faster than everyone else or somehow they're experiencing slower. Either way, how does that fit with this?
Jonathan Colvin
Not sure how with this works with special relativity, although presumably it does. Does a moving observer travelling close to the speed of light create space relative to a stationary observer?