17 minutes ago, Wildblue said:

O was the Grandfather paradox not about when you kill your grandfather he can't have made your father and your father can't have made you so you immediately cease to 

 

Or, when you go back in time and kill your grandfather, it creates an alternate time line where you don't exist in the future. But then you return to your own time line where your grandfather wasn't killed and you do exist.

That way there is no paradox, it's about alternate time lines, like the branches of a tree.

Hawking argued that there would be an aspect of nature that prevents time travel, his chronological protection  conjecture. But we simply don't know. We don't understand time.

Edited March 6, 20233 yr by martin-w

5 hours ago, martin-w said:

The crisis exists, but its in terns of physics that deals with fundamental particles and fields. Its a subset of physics.

In another subset of physics, there's a bit of "tension" over the Hubble Constant:

https://bigthink.com/hard-science/hubble-tension-cosmology-crisis/ 

Edited March 6, 20233 yr by dmwalker

I don't consider "time" to be a concrete thing.  It is an abstract concept.  We self-aware, conscious beings have created the concept of time to measure velocities, and as a measurement for when things occur relative to one another, IE this happened so many units of time before or after that.

The illusion of time dilation at high velocities or in a strong gravitational field is actually relative velocities being slower so processes occur at a relatively slower rate.

I do not see time as an actual dimension.

Time travel is not possible because time doesn't actually exist.

Dave

Edited March 6, 20233 yr by dave2013

2 hours ago, dmwalker said:

In another subset of physics, there's a bit of "tension" over the Hubble Constant:

https://bigthink.com/hard-science/hubble-tension-cosmology-crisis/ 

 

Tension here, tension there, puzzles here puzzles there... but physics as a whole is not in crisis. 

https://www.forbes.com/sites/chadorzel/2019/01/15/physics-is-not-in-crisis/?sh=ffb8837174cc

23 hours ago, martin-w said:

Thing is, we don't understand then true nature of time, why it flows. There are scientists like Carlo Rovelli that believe time, as we perceive it, is an illusion.

Time is a man-made invention.  Like a yardstick.  It is measurement agreed upon by everyone as a convenient way to measure the period of earth's rotation about its axis and its rotation around the sun in its orbit.  And why Jupiter days are different from Earth days,

Like distance and weight measurements.  Pounds or grams.  Inches or millimeters.  Miles or kilometers.

We humans who suspect ourselves as being intelligent beings debate the aspects of time.  But what about beings not as intelligent as ourselves?

Do dogs and cats have a concept of time?  Do they know how old they are?  Do they know the time of day aside from it being light or dark outside?  Do they think about what they are going to do tomorrow?  Do they think about the future or about the past?  And how would we know if our pets could tell time?

Someone is going to reply that their pet knows when it's feeding time.  Is that cat or dog conscious of time or is it just hungry?  My cat's bowls are always filled so they feed all day long.  Are they conscious if time?

We are conscious of time because we invented devices to measure it. 

Noel

But there must be something like time because living beings, and even things, are indisputably getting older. What do physicists say about that?

And why is time always going forward and never backward? Could there be a universe where you start old and end young?

Questions from a layman, i know, but just curious.

 

47 minutes ago, birdguy said:

1. Do dogs and cats have a concept of time?  2. Do they know how old they are?  3. Do they know the time of day aside from it being light or dark outside?  4. Do they think about what they are going to do tomorrow?  5. Do they think about the future or about the past?

 

Depends on the animal. Some lower life forms are probably just biological machines with no consciousness. Whereas other animals are as conscious as we are. I would imagine there is a threshold in terms of neurological development where consciousness arises. 

So given the above, I'll just refer to cats, as they are awesome. 😺

1. A study from Northwestern University said yes. 

2. Precisely, I wouldn't think so. 

3. Yes, they have a natural body clock.

4. We don't know because we can't read their minds. But increasingly we are learning that humans aren't as special as we thought, and animals are more capable than we thought.

5. Yes, cats have excellent long terms memories according to research.

 

59 minutes ago, birdguy said:

We are conscious of time because we invented devices to measure it. 

 

We were conscious of time before we invented devices to measure it. 

2 minutes ago, Wildblue said:

But there must be something like time because living beings, and even things, are indisputably getting older. What do physicists say about that?

 

Getting older is an example of "entropy" the tendency for things to become more disordered. It has been suggested that time is precisely that, entropy.

As I said before, we don't understand time. Not much can be said that is definitive. If the "Block Universe" is true then the past, present and future all exist, and we humans are stuck travelling along the time dimension, without being able to see the bigger picture. So time is certainly real for us, from our perspective, but the bigger picture may be that all time is real, the past, the present and the future.

Another suggestion is the Growing Block Universe. It suggest that the past and present are real, and the future isn't yet.

 

 

1 hour ago, birdguy said:

Time is a man-made invention

Time exists whether we exist or not. The measurement of time is the man-made invention.

1 hour ago, birdguy said:

We are conscious of time because we invented devices to measure it. 

It's the other way round. We are conscious of time so we invented devices to measure it.

What I am after here are animals aware of time?  Are they aware of any dimensions?

A squirrel buries a nut and a month later he remembers where the nut is and goes back and digs it up but does he remember when he buried it?

A gazelle runs 100 yards in X number of minutes.  Is that gazelle aware of the distance it ran or how long it took him?

Or are we humans the only creatures who are aware of and create measurements of time and distance?

Noel

15 hours ago, birdguy said:

What I am after here are animals aware of time?

 

As I mentioned. Yes, research says yes. But it depends on the species. 

 

Quote

A squirrel buries a nut and a month later he remembers where the nut is and goes back and digs it up but does he remember when he buried it?

 

Yes, they bury them near landmarks, like oak trees etc. They remember the tree where they buried them.

 

Quote

A gazelle runs 100 yards in X number of minutes.  Is that gazelle aware of the distance it ran or how long it took him?

 

Probably not, no evolutionary reason to sense and remember such data. 

Edited March 7, 20233 yr by martin-w

20 hours ago, birdguy said:

A squirrel buries a nut and a month later he remembers where the nut is and goes back and digs it up but does he remember when he buried it?

There was a 3M commercial once, showing a squirrel burying nuts. The end of the commercial showed the inside of its nest lined with Post It Notes showing the locations.

On 3/5/2023 at 2:15 AM, birdguy said:

Interesting article but I don't believe a word of it.  Traveling back in time means resurrecting people who are long dead.  How do you do that?  Maybe resurrecting vision of the past from light waves that are still travelling through the universe might be theoretically possible actually walking through a city like San Francisco in 1906 and experiencing the earthquake and shaking hands with people who have turned to dust is inconceivable to me.  It means more than just travelling to the past.  It means reconstructing the past.  The people...the infrastructure...the geography...the events and their causes.

It can mean whatever the person describing time travel wants it to be. However, time travel to the past seems impossible per one of Stephen Hawking's conjectures on time travel.
Watch this video podcast by Neil deGrasse Tyson and Brian Greene referencing this point, here: https://youtu.be/siX1pLhRXuM?t=1386

 

On 3/5/2023 at 10:15 AM, Wildblue said:

The "Grandfather paradox" is on this.

Same video podcast by Neil deGrasse Tyson and Brian Greene discussing the constraints of time travel to the past, here: https://youtu.be/siX1pLhRXuM?t=745

There is, however, a theory for the Grandfather paradox to exist. It involves quantum physics and the multiverse model.

Quote

[A] second approach to traveling back in time invokes quantum physics, where an event may have several possible outcomes with different likelihoods of occurring.

As described by the Stanford Encyclopedia of Philosophy, the "many worlds" interpretation of quantum theory sees all these various outcomes as occurring in different, "parallel" timelines. In this view, the grandfather paradox could be resolved if the time traveler starts out in a timeline where their grandfather lived long enough to have children, and then — after going back and killing their forebear — continue along a parallel time track in which they will never be born.

More in this article: https://www.livescience.com/grandfather-paradox

 

On 3/5/2023 at 3:34 PM, martin-w said:

Thing is, we don't understand then true nature of time, why it flows. There are scientists like Carlo Rovelli that believe time, as we perceive it, is an illusion.

Albert wrote... 

There as a concept called "Block Time".

https://plus.maths.org/content/why-block-time#:~:text=Block time is all of,mathematical artefact of the physics".

https://plus.maths.org/content/what-block-time

Imagine a layer cake. The cake has three dimensions, but we need to pretend that the fourth dimension of time is the layers, all of space and time are present within the cake. The past, the future, the present, all exist, just not where you are now, now is just the present.

Interesing.

Another theory suggests that there are two arrows of time, fowards and backwards, and that they are asymmetrical. This can be seen by the way certain subatomic particles behave.
More in this article: https://www.sciencealert.com/a-physicist-has-a-new-explanation-for-why-time-moves-forwards-not-backwards