Time ran slower in the past, study finds
Image: Thomas Quine via Flickr
Physicists from the University of Queensland in Australia have found evidence that time ran slower in the past. This may sound like they climbed into the attic and excavated a dial-up modem, but it’s actually to do with supernovae. Let’s have a look.
You have probably heard of cosmological redshift, which means that light from faraway galaxies is shifted to the red as it travels towards us. This happens because the universe expands as the light travels and that stretches the wave-length of light. So it becomes more red.
This cosmological redshift is how we know that the expansion of the universe is actually speeding up. A Nobel Prize was awarded for this in 2011. You’ve probably heard of this, but what’s far less well known is that shifting light to the red is not the only thing the expansion of the universe does.
Another effect is that when we look back in time, everything seems to happen slower. It’s called “Time Dilation” in general, or “cosmological time dilation” in this particular case. Indeed, the two things, redshift and time dilation, necessarily go together.
Think about it this way, if you have a wave you could use each crest of the wave as a tick of a clock. Now if the wave shifts to the red, it stretches, and those time markers move apart. It’s a direct consequence of Einstein’s theory of general relativity.
And yes, this time-dilation is the same effect that slows down time near a black hole. You see, if you are near a black hole and you want to send a signal to someone far away, then the signal needs to escape, so it has to work against the pull of gravity. But it can’t slow down because light always moves with, well, the speed of light.
So rather than slowing down, the light instead loses energy, and that means that its frequency becomes smaller and the wavelength longer. It gets redshifted.
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