Newbie question.... The Big Bang & The Observable Universe (and time)

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Discussion Overview

The discussion revolves around the concepts of the Big Bang, the observable universe, and the nature of time as it relates to light travel and observation. Participants explore the implications of observing distant galaxies and the understanding of time in the context of cosmological events.

Discussion Character

  • Exploratory
  • Debate/contested
  • Conceptual clarification

Main Points Raised

  • Some participants express confusion about the idea that observing distant galaxies means seeing the past and question whether it implies the possibility of seeing the future by pointing telescopes in specific directions.
  • It is noted that light travels at a finite speed, which means that observations of celestial objects are always of their past states, and this does not allow for future observations.
  • There is a contention regarding whether the Big Bang represents a discernible point of origin, with some arguing that it does not predict a point of origin and others questioning this assertion.
  • One participant proposes a thought experiment involving sending spaceships in all directions and asks whether they would be considered to be in the past or the future, leading to discussions about time lag due to the finite speed of light.
  • An analogy is presented comparing the universe to a medieval empire with couriers delivering outdated news, illustrating the delay in receiving information from distant galaxies.
  • Concerns are raised about the nature of time during the Big Bang and whether time was a fixed law at that moment, with some suggesting that time may not have been fixed before the expansion.
  • Participants discuss the meaning of time intervals in the context of inflationary theory, questioning whether time measurements hold significance if they are uniform across the universe.

Areas of Agreement / Disagreement

Participants express a variety of views on the nature of the Big Bang and the implications of observing the universe. There is no consensus on whether the Big Bang represents a point of origin, and discussions about the nature of time and light travel reveal differing interpretations and uncertainties.

Contextual Notes

Some statements rely on assumptions about the nature of time and the Big Bang that are not universally accepted. The discussion includes unresolved questions about the implications of light travel time and the interpretation of cosmological models.

revv
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I am trying to understand some things but I seem to be confused a little...

I was watching a video and it said when you look with hubbles telescope you see the past universe but I seem to have trouble understanding this, does that mean we could see the future if we knew which direction to point the telescope at?

I don't know if this makes any sense... hopefully it does :/
 
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Well, remember that light doesn't travel from one place to another instantly. It has a velocity of about 180,000 miles per second. So when you look at the Moon, which is about 200,000 miles away, it has taken light a little over 1 second to travel from the Moon to your eye. So whatever happens on the Moon "now" will be seen one second from now. For galaxies that are billions of light years away, we are literally seeing the ancient past because it has taken billions of years for the light to reach us.

revv said:
does that mean we could see the future if we knew which direction to point the telescope at?

It does not.
 
You appear to assume the universe has a discernable point of origin - it does not.
 
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Chronos said:
You appear to assume the universe has a discernable point of origin - it does not.

Isn't the big bang a point of origin?
 
revv said:
Isn't the big bang a point of origin?

It is not. The big bang theory doesn't even predict a point of origin. All it says is that the universe was originally in a very hot, very dense state and expanded and cooled from there. At no point is the size of the universe ever predicted to be zero.
 
Lets say you where to send space ships in EVERY direction from Earth into outer space... would they all be considered to be in the past or would some be going into the future?

If not what exactly would happen if we where to do just that?

Sorry if this doesn't make sense I am just really trying to understand but I have trouble...
 
The departing space ships would suffer from time lag compared to time measured on Earth due to the finite speed of light. So, you could say they will all journey into our future past
 
revv said:
Lets say you where to send space ships in EVERY direction from Earth into outer space... would they all be considered to be in the past or would some be going into the future?

If not what exactly would happen if we where to do just that?
Consider an analogy:

The universe is represented by some large medieval or ancient country, say the Roman empire at its peak. Instead of light signals we have couriers traveling by horse with missives.

Say, there is a system, where each province of the empire sends a courier each day with the most up-to-date news about local state of affairs to the capital.
The couriers need several days to get to the destination - those from nearby as little as one day, those from farther reaches many days.

So, assuming this has been going on long enough for at least one courier from each province to get there, each day, an official (observer) in Rome receives a courier from every province. All couriers carry news that are outdated at the time of reception. The report from a one-day-away province is one day old, the report from a 9-day-away province is 9 days old.

The scenario in your question is analogous with the official sending back some information to all provinces, and order to muster troops for example.
Some couriers will start their return journey on more outdated information than others (maybe the province has been overrun by barbarians in the five or so days it took the latest courier to get to Rome), those also will get there later than others, and the information they eventually send back will be also delayed more.

It's all in the delay caused by signal travel time, but nobody is doing any time traveling here, apart from the mundane sense of traveling into the future one second at a time like we all do.
 
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Bandersnatch said:
Say, there is a system, where each province of the empire sends a courier each day with the most up-to-date news about local state of affairs to the capital.

If I understand correctly "Local state of affairs" would be the matter in the universe?
 
  • #10
revv said:
If I understand correctly "Local state of affairs" would be the matter in the universe?
The state of that matter. The courier is analogous to the light beam carrying information about that state, i.e. how the province/galaxy looked at the time the courier/light was leaving/was being emitted.

When you receive a courier, you only get to know how about the state in the province at the time he was leaving. When you receive (see) light from a distant galaxy, you only get to know what it tells you about the state the galaxy was when it was leaving.
 
  • #11
Newbie alert..

I thought this would be a good thread to jump into because of the (and time) bit in the topic.
I have always been trouble by the hyperinflation part of the big bang, something conjured up to explain the expansion faster than it should have.
Could it be that at the time of the "Big bang" before any laws of the universe existed, time was not a fixed law, and that time was only "fixed" like all the other laws after the initial expansion. Therefore the initial expansion could have taken its time, so to speak.
 
  • #12
toadoftoadhall said:
Could it be that at the time of the "Big bang" before any laws of the universe existed, time was not a fixed law

Time is not a "law"; it's a coordinate (or a parameter along timelike worldlines). The inflationary scenario includes the time coordinate/parameter; so when cosmologists talk about the era of inflation taking only ##10^{-32}## seconds (or whatever the time is), that's not adjustable, it's part of the model.
 
  • #13
but couldn't 10−32 seconds be meaningless, I mean if time, was stretched at the BB.
 
  • #14
toadoftoadhall said:
but couldn't 10−32 seconds be meaningless, I mean if time, was stretched at the BB.

It only matters if there was a difference in the rate of time between different parts of the universe. If the change in time is the same everywhere, then there's no way to measure it and it has no real meaning.
 
  • #15
revv said:
I was watching a video and it said when you look with hubbles telescope you see the past universe...

As noted, that's because light takes time to get here.

It also means that light carrying the information from an earlier time is coming towards us, no matter which way we look. Light comes TOWARDS us for every direction. If light were only passing us by, we could see nothing in some directions...where the light is receding from us.

That's a huge clue that the origin of that light was not a point in space;Not like a light bulb, for example. Like looking away from the direction of the light bulb...then you can't 'see' it.
 
  • #16
revv said:
I am trying to understand some things but I seem to be confused a little...

I was watching a video and it said when you look with hubbles telescope you see the past universe but I seem to have trouble understanding this, does that mean we could see the future if we knew which direction to point the telescope at?

I don't know if this makes any sense... hopefully it does :/

Another way to put this is that, while all of the universe is basically at the same point in time but because information in the form of light takes time to arrive the observer "you" don't know what happened until the information arrives and because this delay is greater at farther distances the older the information is when it arrives, It is the same principle as the lightning-thunder delay in the way that the sound of the thunder travels "slowly" thus the sound doesn't arrive for several seconds.
 

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