The universe is expanding at an ever-accelerating rate. At least, that’s what the vast majority of scientists would have you believe. But according to a team of Spanish physicists, it may not be the expansion of the universe that’s changing rate, but time itself. Time might be slowing down, and that means that it could eventually stop altogether.
Tick … Tick … Tick …
To illustrate what José Senovilla at the University of the Basque Country in Bilbao, Spain, and his team are getting at, think about what it sounds like when an ambulance passes you on the street, sirens blazing. As it drives away from you, the siren begins to drop in pitch. This is known as the Doppler effect, and it happens because the sound waves ever so slightly stretch as the ambulance drives away from you, meaning they reach you at a slower rate (i.e. a lower frequency).
But what if the laws of physics changed when that ambulance passed, and instead of its speed causing that drop in frequency, it was the passage of time? If time were slowing down, that would also make the sound waves reach you at a lower frequency. That’s essentially what Senovilla’s team is suggesting. We “know” the universe is expanding at an accelerating rate because galaxies further away from us have a greater redshift — light’s version of that ambulance Doppler effect — than galaxies closer to us, meaning they’re moving faster. But if time were slowing down, the light would just reach us at a lower frequency. We’d see the redshift, but it would be for a different reason.
The universe is not actually “expanding”. You see, if there is an object with a certain mass, and if you add more mass to it, then we say the object is expanding. The meaning of the word “expand” in this context, is to “become larger”. That is not what is happening to the universe. The right word may be “stretching”. The question of “what the universe is expanding into” arises when we imagine that there are billions of galaxies – which we know as the universe – floating in space, having started at some center point and are now moving at high speed away from that point and from each other. This is not what is happening.
This theory sounds outlandish, but it fixes some nagging problems. For the universe’s expansion to be accelerating, you need to come up with something to cause it. That’s where so-called “dark energy” comes in. This mysterious force is supposed to make up 68 percent of the universe, but we’ve never actually observed it. If time is slowing down instead, you don’t need dark energy at all. The mystery of dark energy is fixed since it never existed in the first place.
Slow Down, Your String’s Too Fast
But this theory gets weirder. That’s because it’s based on a principle in string theory that says our universe exists on the surface of a membrane — a “brane,” in string-theory speak — that itself exists inside a higher-dimensional space called the “bulk,” aka hyperspace. All branes can have different numbers of dimensions; ours happens to have three spatial dimensions and one time dimension, but others could have no time dimensions or multiple time dimensions. Dimensions in those other branes could even swing between different versions: space could become time, and vice versa. That’s what the researchers think might be happening to our time dimension: it’s slowly turning into a space dimension. If it succeeded, our universe would be frozen in time and exist in four-dimensional space.
We’d experience this as a gradual slowing of time — so gradual, in fact, that for the first billion years or so, we’d only see its evidence in grand scales, like the movement of faraway galaxies. “Our calculations show that we would think that the expansion of the universe is accelerating,” Senovilla told New Scientist. “[Any] observation of dark energy could be evidence that our brane is changing signature and that time is disappearing.”
But if this sounds alarming, don’t worry: this won’t happen for billions of years. In the meantime, buck up! Life is longer than you thought.