What's happening in the universe right now?

January 30, 2015 by Fraser Cain, Universe Today
Betelgeuse, as seen by the Hubble Space Telescope.

There are some topics that get a little frustrating in their pedantry, but can really draw attention to the grand scope and mechanics in our Universe. This is definitely one of them.

We know looking through a telescope is like looking into the past, both out from and towards our Earth. We know if alien ships were looking at the Earth right this moment from distant star systems they'd could well be watching dinosaurs chomping on each other's adorable little faces.

So how do we know what's actually going on right now in other parts of the Universe? No matter how close together, the real challenge of defining "now" simultaneously for two different spots in the Universe is that these points are always separated by a bit of distance. Since nothing can travel faster than light, it will always take a some time for an indicator that an event has "happened" to reach you.

So, on the small scale. If your friend 3 meters away from you says "Enterprise was a terrible show" right "now", it will still take about 10 nanoseconds for the light of your friend to reach you. It will take about 8 milliseconds for the sound of your friend's voice to reach you. Shortly thereafter you'll decide to slap your friend, because seriously who needs that kind of negativity. You might say that is close enough to be the same "now". As in "I slapped my friend just now, because he said something stupid".

If Dr. Who has taught us anything, it’s that time is kind of crazy. And we’re not just talking about time travel here, we’re talking about regular old “now”. Well, what “now” means depends on where you are and how fast you’re moving.

For how our brains perceive time, and the relative length of our lifespans, you probably can get away with it, because sure, that's "now". We can consider a moment to occupy a span to encompass all these events. Although, you shouldn't slap your friends. Even if they say mean things, and really didn't give it a chance. You're lucky your friend won't have to wait too long to hear an apology from you as milliseconds after you say you're sorry, they'll hear you. Which, for our purposes, would be "right now".

Over larger distances this doesn't quite work as well. If you looked up in the sky and saw Betelgeuse become a , would you argue that it is happening now? Some people might say yes. Until you know about an event, you can't say it is happening. So, "Hey look, that star is going supernova right now" is what your brain might think. You received an indicator the event is beginning to happen, which for our purposes indicates it just started "now".

Except, as one of our viewers, you're way too smart for that. You would argue that since Betelgeuse is 640 light years away, the supernova actually happened 640 years ago, and it's just taken that long for the light to reach us. We're all good so far, as soon as I started talking about light years, you knew what was going on. It looks like it just happened now, but we're aware that's not the case. It happened before, we're only aware it's happening now.

Here is where it gets weird. The most yet discovered is z8 GND 5296. It's 3.4 billion light years away. If we happened to observe a supernova in that distant galaxy, when would we say it happened? Obviously it's not "just now".

Galaxy z8_GND_5296 (seen in the inset) is the earliest galaxy that astronomers have measured the distance to accurately. It formed approximately 700 million years after the Big Bang, and is forming stars at an incredibly rapid rate. Credit: V. Tilvi (Texas A&M), S. Finkelstein (UT Austin), the CANDELS team, and HST/NASA

When the light we currently observe left that galaxy, it was about 3.4 billion away. So should we say it happened 3.4 billion years ago?Sure sounds reasonable based on our Betegeuse example. However, since our Universe has been expanding, it actually took the light 13.1 billion years to reach us. So we could say it happened 13.1 billion years ago.

Which one do we use? The real catch is that there is no cosmic definition of "now" in the Universe. Because of special relativity, the rate at which time flows for a particular object depends upon your point of view and your velocity. For a rocket travelling near the speed of , a journey to Alpha Centauri might take a week. For us it would seem like 4 years. As a result of relativity, even the meaning of "simultaneous" is relative to your point of view.

The answer to what is happening now, is "it depends". It depends on your frame of reference, and how flexible your attitudes about "now" are, what constitutes a moment, and quite probably how long lived your species is. I'm sure Jack Harkness and the nigh eternal Face Of Boe would give very different answers, well at least, depending on when you asked them.

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14 comments

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cantdrive85
2.3 / 5 (6) Jan 30, 2015
Fraser Cain needs to be slapped for saying something stupid, continuously.
Mark Thomas
3 / 5 (4) Jan 30, 2015
"nothing can travel faster than light" is inaccurate shorthand. Perhaps more accurately one might say nothing can travel faster than light in a vacuum, that is not just a pattern, that didn't start off traveling faster than the speed of light (tachyon), without relying on quantum mechanical effects (tunneling, entanglement collapse), that is not in a portion of space that is itself traveling (Alcubierre Warp Drive), that is not in a wormhole (Einstein-Rosen Bridge), and anything else we haven't figured out just yet.

Urgelt
3 / 5 (2) Jan 30, 2015
Lorentz wasn't so sure that 'now' couldn't exist for the entire universe. And that's why he offered the Absolute Lorentz Transformation, which treats the entire universe as a single frame of reference.

In this frame, the rate of flowing time can vary in specific locations, so the length of the past can vary by location. But it can all be lined up on a timeline 'now.' This frame ignores the crawling of light between different objects. That's happening, but it doesn't invalidate the 'now' of the universe.

SR establishes the relationship between moving objects; GR grinds in gravity; both rely on Lorentz Transformations. Neither one looks at the entire universe as a single frame. But neither SR nor GR rules it out, either.

It should be possible to determine experimentally if the Absolute Lorentz Transformation is valid; it has specific, if subtle, implications for how time dilation works, and that could be tested. Alas, thus far, no-one has bothered to look.
the-truth-seeker
3 / 5 (2) Jan 30, 2015
Good explanation. But there is also the problem of what is, and what is not, an inertial frame of reference! Relativity only works if you know what is an inertial frame of reference. Not everything in the universe can be one.
Urgelt
1 / 5 (1) Jan 31, 2015
Truth Seeker, that's certainly true for either SR or GR. They aren't set up for a universal frame.

The principle objection to Lorentz's ALT is that it supposedly puts Earth at the center of the universe - which neither SR or GR permits.

But that objection isn't true. Lorentz's absolute frame works for any observer at any location. The caveat is that it requires time dilation to be directional and not reciprocal. ALT contradicts SR.

Edward Kipreos pointed out in a recent paper that there is no experimental proof for SR's reciprocal time dilation. All of the time dilation experiments conducted to date either prove time dilation exists (without commenting on reciprocity or direction), or proves time dilation works in one direction (GPS).

That doesn't mean ALT is proven. It only means it hasn't been ruled out.

Reference frames are the mushiest part of relativity theory. Defining them has always been awkward and questionable. Lorentz sought to solve it. Maybe he did.
Mr Som-o
3 / 5 (2) Feb 01, 2015
Food for thought alright. What we see as happening 3.4 BY ago, but taking 13.1 BY to get here.
Whydening Gyre
3 / 5 (2) Feb 01, 2015
It should be possible to determine experimentally if the Absolute Lorentz Transformation is valid; it has specific, if subtle, implications for how time dilation works, and that could be tested. Alas, thus far, no-one has bothered to look.


Your mission, should you choose to accept it...
Urgelt
3.7 / 5 (3) Feb 01, 2015
"Your mission, should you choose to accept it...:"

Heh! I'm a crank without credentials, a laboratory or funds- just like almost all of the posters here. ALT appeals to the crank in me, though I do not pretend to know if Lorentz was correct or not. (I'm crankish, but I don't take it to extremes!)

If he was correct, though...

Cosmology will require a vast overhaul. ALL cosmological measurements rely on red shift. If we *should* be compensating for time dilation in red shift, then all of our measurements require correction. Every single one. Dark Energy, Dark Matter, Cosmic Inlfation, the age of the universe, all of our conclusions and deductions are wrong.

That's definitely crank territory! But then, to defend contemporary cosmology without bothering to investigate SR's reciprocal time dilation, we have to dismiss Lorentz himself as a crank, too.

That might not be the wisest course. Lorentz's importance to modern physics can't be overstated.
Whydening Gyre
3 / 5 (2) Feb 01, 2015
Food for thought alright. What we see as happening 3.4 BY ago, but taking 13.1 BY to get here.

Definitely taking the scenic route...
big_hairy_jimbo
5 / 5 (1) Feb 01, 2015
Food for thought alright. What we see as happening 3.4 BY ago, but taking 13.1 BY to get here.

Definitely taking the scenic route...


I think the light is hitching a ride with my local pizza delivery driver.
Whydening Gyre
3 / 5 (2) Feb 01, 2015
Food for thought alright. What we see as happening 3.4 BY ago, but taking 13.1 BY to get here.

Definitely taking the scenic route...


I think the light is hitching a ride with my local pizza delivery driver.

Just an interesting note. A real ruff calculation indicates that the "Big Bang" light is moving away at ruffly 3.425 times the speed of light...
Just an artist, so math skills may be a little off... Anybody else have input on this?
Urgelt
3.7 / 5 (3) Feb 02, 2015
"Just an interesting note. A real ruff calculation indicates that the "Big Bang" light is moving away at ruffly 3.425 times the speed of light..."

If we should be adjusting red shift to account for time dilation, it'll be a lot less.

We can't know if we should adjust for time dilation until SR's reciprocal time dilation is proved or falsified. Lorentz is in one corner, Einstein is in the other. One of them is right.
vidyunmaya
5 / 5 (1) Feb 02, 2015
Many thanks for the post. Good education . Please keep-up -Awakening
Whydening Gyre
3 / 5 (2) Feb 02, 2015
We can't know if we should adjust for time dilation until SR's reciprocal time dilation is proved or falsified. Lorentz is in one corner, Einstein is in the other. One of them is right.

Not sure, but at this particular juncture, I am inclined towards Lorentz?...

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