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When we look at very distant objects in the universe we're looking at how they were many millions of years ago.
Therefore they're appearing younger than they are now, and many of them probably no longer exist.
In the first few 100s of milllions of years after the big bang happened everything was much closer together, and the universe is still expanding, as everything is getting further away than everything else.
That much I get.
So when we look VERY far into the distance, we're looking at objects that, when the photons we are seeing were given off, were closer to us than they are now. So is it true that, the further away we look, the closer to us we look? And, if so, could we ultimately see ourselves in the distance, theoretically?
Also, the galaxy HD1 appears (!) to be the farthest known object, as it's 13.1 billion light years away. But surely it WAS when the light we see was given off. It can't still be there now, as it's had 13.1 BLY to move further away? So if we were to see 13.7 BLY away we'd be seeing the big bang, of which we are a primordial part.
Stuff makes no sense. What's your take on this?
It's because, simply put, the galaxies are moving away from us very fast, so the photons have taken a long time to reach us even though they were 'close' when they set off.
Complicatedly put involves maths with which I am not familiar, I didn't do general relativity at uni. And if I had, I wouldn't have been listening and I'd have forgotten it by now anyway.
we’d be seeing the big bang
We can see the big bang, or what's left of it - it's called Cosmic Background Radiation and it's everywhere.
Your question raises an interesting thing.
Time slows down the faster you go, apparently. So where does the universe age of 13.7 billion years come from?
If you asked one of the photons released from the big bang (which was still travelling unhindered today) how old it was it would look at it's watch and say "it's still on zero, mate".
Time slows down the faster you go, apparently.
Not for you, no. For other people. Your photon's watch would say 13.7bn years, same as yours. It's because information, even cause and effect cannot go faster than light. So you can't actually ask it. Your watch and its watch would say the same but you could never see its watch. You can only see its watch as it was 13.7bn years ago.
Time slows down the faster you go, apparently. So where does the universe age of 13.7 billion years come from?
Relativity explains how to correct for time dilation from your perspective. So it’s not too difficult to unwind it back to the beginning. If you subscribe to the inflation theory it all happened in the first few seconds, so the 13.7 billion years bit is the easy bit.
The true age of the universe is measured by cutting it in half and counting the rings.
Time does not exist for photons, as they travel at the speed of light.
The cosmic background radiation that we observe was actually produced 380,000 years after the big bang so the universe was smaller but still very big.
The universe also expanded faster than the speed of light, so there's large parts we will never see or interact with in any way.
Also, I got all this from chatgpt.
Time slows down the faster you go, apparently.
Unless you're speeding out of Trumpton with a cargo of cocaine. Then it positively flies by.
IMO the question as posed in the OP doesn't make any sense, because that's not how "looking" works - you don't "look" further into the distance, you just stay where you are and wait for the light/whatever to get to you!
There's a podcast I listen to called "Daniel and Jorge Explain the Universe" which explains all this kind of stuff really well to the layman (although often I need to listen to it a few times before something clicks!)
But you are all wrong if Kang (from the latest Ant-Man film) is to be believed. 🤣
So is it true that, the further away we look, the closer to us we look?
Not really, the further away you look the further into the past you look.
And, if so, could we ultimately see ourselves in the distance, theoretically?
No. The speed of light is essentially the maximum speed at which information can travel.
Not really, the further away you look the further into the past you look.
But the further into the past you look the closer to us (and everything else) the observed things 'were'. If you take that to its extreme we'd see the moment of the big bang when everything was compressed into one small space, not the CB radiation remnant but the actual moment.
Early on the Universe was so dense that photons couldn't travel about freely, they bumped into things and got absorbed.
Also, I got all this from chatgpt.
Impressive. I wonder if it scanned my PhD.
A former professional cosmologists writes (and I’m very rusty!)…
it’s not that they are really closer. It’s that space-time is expanding. A “ruler” used to measure the “distance” between objects would also have stretched. And the light travelling between them runs at the same speed in that frame of reference.
We like the surface of the balloon analogy because the universe is like that (but in three not two dimensions). The balloon is expanding and on the surface things appear to move further apart. In fact if you graded the distance between two objects, the marker lines would be getting further apart too. That’s the distance part of space time. So in the reference point of being on the ballon surface, things aren’t getting further apart because the measurement tool is also getting longer.
The “volume” of the balloon is also increasing and would have been smaller, and zero, at the big band of about 14bn years ago. What we observe unidirectionally in the background radiation is an after flow of a transition in state. It’s smoothness likely disproved one of the hypotheses I worked on and led to the notion of inflation-driven formation of those blobs on the ballon surface.
Hope that’s relatively clear. I did study General Relativity and Riemann geometry. It’s one reason why I now do biology 😉
The YouTube video at the top is by Fermilab. If you follow that back to YouTube, their channel has a lot of videos that answer the main questions in this thread.
In fact if you graded the distance between two objects, the marker lines would be getting further apart too.
I don't like that explanation. If spacetime is simply expanding, then the ruler I use to measure the wavelength of light from distant objects is also expanding. So how does expanding space account for the red shift? I feel there's another relativistic explanation that is just out of reach of my current state of mind.
I did study General Relativity and Riemann geometry. It’s one reason why I now do biology
When I read this, there are two possibilities that spring to mind:
1) Astrophysics is too hard for TiRed's tiny* brain
2) There's something translational about Riemann geoemtries that lends itself to understanding biology
Unfortunately I'm too dim to work out whether he's being smart or self-effacing.
* I hear those prizewinning MABs basically invent themselves on ChatGPT these days.
it isn't AFAIK. It's only the less-dense areas that are expanding like that, Areas such as our solar system are held together by forces - gravity (and maybe quantum forces? been a long time since I did physics)If spacetime is simply expanding, then the ruler I use to measure the wavelength of light from distant objects is also expanding.
In fact I think ultimately our galaxy will mash together with our closest neighbours due to these attractive forces?
So how does expanding space account for the red shift?
The speed of light is invariant. If space expands, the wavelength of light is stretched and the frequency reduced.
It’s only the less-dense areas that are expanding like that,
The entire universe is expanding. This is happening over distances and timescales beyond our everyday experience. It won't make any measurable difference within our lifetimes, but over untold billions of years, the universe will just become a cold, dark void. Particles of matter will eventually be so far apart that they will almost never interact.
1) Astrophysics is too hard for TiRed’s tiny* brain
I enjoyed it, but the half-life in theoretical physics is about two years. I did secure a post-doc in the subject though. Hence “professional”. But then I moved to Mathematical Biology and eventually Clinical Pharmacology. I don’t miss the physics, but by heck it’s hard maths. And I much prefer the alternative to the one most of my colleagues took, which was financial engineering. BTW Neil Ferguson received the same physics to biology fellowship as myself, just a year later. We shared an office.
If space expands, the wavelength of light is stretched
Hmm. If there are three gradations between dots on the balloon, and you inflate the balloon, there are still three gradations between the two dots. Wavelength is measured in metres, but the meter is also expanding.
I think I have been through this in my head before and there is a relativistic explanation but it's eluding me currently.
no, that’s not right AFAIKParticles of matter will eventually be so far apart that they will almost never interact.
I have no comprehension, or the brain facility to comprehend, the topic discussed above. No matter how simplified etc. My brain doesn't function in a way for any of this to make any sense whatsoever. I've tried. What I do often wonder, however, as I marvel at the night sky, is, if the universe is expanding, what the hell is it expanding into, and what heck is on the 'other side' of its outer edge???? 🤯🤯🤯🤯 (no answers required - I won't understand them anyway😁)
It’s the constant speed of light that pulls together the dissonance. Without that law, since verified multiple times, relativity and general relativity fall apart. That was Einstein’s single greatest contribution to the understanding of the universe. It’s very counter intuitive.
Son2 is going to be an airline pilot. A life at speed means time WILL go slower for him (a little bit but detectable by an atomic clock over a lifetime). That sounds utterly crazy. But… bindun
https://en.wikipedia.org/wiki/Hafele%E2%80%93Keating_experiment
Particles of matter will eventually be so far apart that they will almost never interact.
no, that’s not right AFAIK
We're talking about a timescale of untold trillions of years.
https://en.wikipedia.org/wiki/Future_of_an_expanding_universe
@thols2 if you’ve managed to prove that theory then you should probably go and pick up your Nobel prize immediately 😂
if you’ve managed to prove that theory then you should probably go and pick up your Nobel prize immediately
If you think that the universe is expanding at different rates depending on the density, you don't understand the basic concept of an expanding universe.
There are three basic possibilities for the topology of the universe: the expansion is slowing down; the expansion is steady; the expansion is accelerating. For the first, the universe will eventually collapse back into a "big crunch", but that doesn't seem to match with the observed evidence. If the expansion doesn't eventually reverse, over unimaginably long timescales, the universe will simply go dark and matter will eventually decay into photons.
No it’s that the atoms in the dense bits are being held together, hence molgrip’s ruler not getting any longer!
thols2
The entire universe is expanding. This is happening over distances and timescales beyond our everyday experience. It won’t make any measurable difference within our lifetimes, but over untold billions of years, the universe will just become a cold, dark void. Particles of matter will eventually be so far apart that they will almost never interact.
As it stands, the fundamental forces still hold particles together. And on a larger scale, gravity holds galaxies together.
It could reach a point where the expansive force (dark energy) is greater than those though. 😵
There's a great PBS Spacetime vid exaplining that once everything decays to photons, the universe will be in the same state it was at the big bang. The universes size will be irrelevant, since the only thing in existence is photons, and photons don't experience time as they travel at the speed of light, which makes distane irrelevant. THen there will be another big bang at the whole thing starts again.
EDIT here it is
So if velocity = distance/time, but the quicker you go the slower time 'ticks', does that mean as your velocity increases it decreases, as if you cover a given distance in double the time you're going slower? Or is the slowing of time only relevant and discernible to the time itself, and nothing else?
'If' at the speed of light time stops, does velocity (v=d/t) = zero, as any number (d) divided by an infinitely large number (t) is infinitely small (or zero?).
And is this science, or philosophy?
And why does it keep me awake in the wee small hours?
So if velocity = distance/time, but the quicker you go the slower time ‘ticks’, does that mean as your velocity increases it decreases, as if you cover a given distance in double the time you’re going slower? Or is the slowing of time only relevant and discernible to the time itself, and nothing else?
Edit- sorry I misread your post.
Let's say you have two twins. One on earth. One travelling in a fast space ship.
Time really is passing slower for the fast moving twin and they will have aged less than their earth based twin when they return!
However both twins each separately perceive time to be running at normal speed.
if velocity = distance/time
That's the Newtonian model.
‘If’ at the speed of light time stops
It doesn't stop for you. To someone watching you it would look like time had stopped. How come? Well, if I were looking at your watch through binoculars as you accelerated away, I would see it slow down because the light you see would be taking longer and longer to get to you. But this isn't just an illusion. Nothing at all can move faster than light, not even information. But if you were to look back at my watch, you'd see the same thing. You'd see time going slower for me.
I think a lot of the confusion here is because people misunderstand what relativity is about. As I recall, Einstein started with the assumptions that the laws of physics are invariant, regardless of your frame of reference (i.e. where you are and how fast you are moving relative to other things), and that the speed of light is invariant. Motion is relative, there is no stationary "ether" that things in the universe more through.
The result of those assumptions is that time and distance are not invariant in the Newtonian sense. Clocks that are in a different frame of reference (i.e. moving relative to us) will appear to us to run at a different speed, but to observers in that frame of reference, it will appear that our clocks are running at a different speed. Everything in our own frame of reference seems to comply with Newtonian laws, but things in other frames of reference do not.
There are mathematical transformations that allow us to translate between different frames of reference, so we can predict the differences between measured time (i.e. how much atomic clocks will differ) if a spaceship is accelerated to high speed and then returned to earth. The astronauts in that spaceship will not notice anything different about themselves or their clock, but they will notice that clocks back on earth run at a different speed and that people on earth age at a different rate.
These differences can be measured. For example, the half-life of cosmic particles appears longer than they should be because they are travelling at very high speeds relative to earth, and atomic clocks in satellites orbiting earth will drift slightly, so GPS systems have to adjust for this.
All of this is just the logical result of the laws of physics being invariant between different frames of reference and the speed of light being invariant. Those constraint mean that time, distance, mass, etc. cannot be invariant in the way that Newtonian physics assumes.
if I were looking at your watch through binoculars as you accelerated away, I would see it slow down because the light you see would be taking longer and longer to get to you
The light equivalent of ambulance sirens changing pitch due to the Doppler Effect?
so GPS systems have to adjust for this
I learnt that just last week from Neil deGrasse Tyson's podcast.
I'm going to find some time to watch all of the above YT vids.
STW never fails to astound me with its knowledge base.
The light equivalent of ambulance sirens changing pitch due to the Doppler Effect?
Exactly.
The light equivalent of ambulance sirens changing pitch due to the Doppler Effect?
No, that happens as well. I can't decide if it's the same thing or not though.
I am not sure my earlier example is actually very good. The fundamental problem as thols2 says is that in a traditional world, lets say I fire a gun and the bullet flies out at 1000m/s - if I get in a car and drive at 30m/s then shoot the gun forwards again, the bullet will now travel at 1030m/s. But if I shine a torch foward, the photons cannot travel any faster. This is the fundamental issue, and all the features of special relativity can be deduced from this. I did have a good mental handle on all this once and I understood Einstein's reasoning, but it seems to have evaporated. If the speed of light really cannot be exceeded then the only possible conclusion from that is that time isn't the same for everyone. There's a Wikipedia page on time dilation which is quite good.
This is the fundamental issue, and all the features of special relativity can be deduced from this.
Anyone got any links to explain why the speed of light is constant? I'm an avid cosmology/physics geek but have seen very little on this subject. It just seems to be one of those things that is accepted as 'it just is'. 🤔
Physics can’t always answer the “why” questions.
Anyone got any links to explain why the speed of light is constant?
Because it's an electromagnetic wave, its speed is derived from electromagnetic constants, which are fundamental properties of the universe and they don't change, therefore the speed does not change.
PS that only applies in a pure vacuum - the constants are different for different materials and hence the speed of light does vary in different media.
Because it’s an electromagnetic wave, its speed is derived from electromagnetic constants, which are fundamental properties of the universe and they don’t change, therefore the speed does not change.
That seems like a bit of a 'it just is' answer though. Is the simple answer that 'we don't know yet'? Or is it 'you can't understand if you don't know the maths'? Both are fine, I was just wondering about what underlying mechanisms makes it constant. Some digging on the internet simply suggests that it's a fundamental constant of the universe and so the question is the same as why any of the fundamental constants are as they are?
dazh
Anyone got any links to explain why the speed of light is constant? I’m an avid cosmology/physics geek but have seen very little on this subject. It just seems to be one of those things that is accepted as ‘it just is’. 🤔
It's not just the speed of light, there is an underlying fundamental constant as feature of spacetime, which is like the speed of causality really.
Light moves at this speed but it is also the speed that massless particles and gravity propagate.
https://www.space.com/speed-of-light-properties-explained.html
The light equivalent of ambulance sirens changing pitch due to the Doppler Effect?
No, that happens as well. I can’t decide if it’s the same thing or not though.
It's fundamentally the same thing. If a light source is moving away from us, the wavelength must increase if the speed is constant. This is called "redshifting". Because the universe is expanding, distant objects are moving away from us, so light from very distant stars is redshifted. Also, space is distorted near massive objects, so light from stars very close to a black hole will be redshifted.
the question is the same as why any of the fundamental constants are as they are?
That's one of the thorniest questions in physics and philosophy. The question is basically whether universes are possible where those values are different from our universe. Those have to be very carefully balanced or the universe will not be stable, so life could not exist. We could only evolve in a stable universe. If they can take other arbitrary values, it could be that we just happened by chance to be in one that took values that can support life. Physicists have modeled conditions to very shortly after the Big Bang, but not close enough to it to understand the parameter setting that determines those constants. In other words, they don't know for sure.
I’m going to find some time to watch all of the above YT vids.
You'd better stay perfectly still then. Or go really really fast. I can't decide which one gets you all that time.
That seems like a bit of a ‘it just is’ answer though.
A small number of things about the universe are intrinsic to it. They just are, in the same way that the universe just is. Because if it weren't, we wouldn't be here to think about it.
I think this is the singularity where Physics, Theology and Philosophy combine into one 🙂
I think this is the singularity where Physics, Theology and Philosophy combine into one 🙂
Yup. I have often wondered about the mindbending question of whether the universe would exist if we weren't here to observe it. By that I mean our observation and understanding of the universe is simply the result of processed signals from our senses, so how can we know if any of it is actually real? I guess it's a fundamental question about the nature of information and intelligence. Trouble is there's not a lot of accessible info out there before you collide with daft hippy shit and stuff like simulation theory. 😀
Another one I struggle with is Quantum Field Theory. The idea that fundamental particles are really only fluctuations in interacting quantum fields (which is my no doubt incorrect limited understanding of it). It essentially boils the whole universerve down to insanely complex mathematical interactions, but doesn't really answer the question of what 'stuff' actually is? And don't get me started on stuff like quantum entanglement. Basically despite all our ridiculously detailed knowledge, it feels like there's much more that we don't know than we do.
I think of it like this: Particles are just probabilities - the closer you are to a point in space the more chance there is of finding an interaction. It's like when you try to push two magnets together at the same pole - you can feel a force pushing them apart. Now imagine that the magnet wasn't there, just the field, and your fingers were the other magnet. You'd be able to feel a squishiness in space. That's what particles are a bit like.
None of it makes any intuitive sense, but it's not meant to. That's not how physicists work. Your intuition about the physical world is the wrong language - the right language is maths. It all makes sense if you speak maths.
Actually, it's more like the language is the formulae, the maths itself is more like your mouth and vocal chords.
Basically despite all our ridiculously detailed knowledge, it feels like there’s much more that we don’t know than we do.
All we do is describe what we see and try to model it so we can predict it.