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# Astrophysics/Expanding Universe

Question
I have had no training in physics but after years of watching all the science programs and searching the net I find I have a problem with "the expansion of the universe is accelerating" theory. All the calculation are based on measuring light that has been in transit for billions of years. Consider, the universe is estimated to be 13.77 billion years old and gravity travels at the speed of light.  If  I measure an object (Type 1a supernova) 10 billion light years away, I am measuring it when the universe was only 3.77 billion years old, and only objects within 3.77 billion ly of the observed object could have exerted any gravitational pull on it at the time of the nova. The problem I have is that I see no way to calculate the current velocities of objects at various distances as gravity is not a constant. Since the effects of gravity are cumulative and distance equals time, the more distant objects should, from our perspective, be moving faster as gravity has had less time to slow them.

Hello,

First, it is risky to use TV science programs as a basis to parse cosmology details, especially when one lacks a physics background. Second, even those with physics - astrophysics backgrounds have to be aware that much of their data is still uncertain, so that no final assessments may be made - or those which are (and often emphasized the most in science programs) may be exaggerated.

This forum is perhaps not the best place to fill in all the details, and I don't have the time to do so, which would mean basically delivering a short physics course on gravitation, basic kinematics, Newtonian dynamics and correcting other misperceptions. For example, gravity does not "travel at the speed of light".  Gravity occurs (and varies)  with deformations of space-time in the vicinty of gravitating masses. (As per Einstein's General Theory of Relativity). The notion of gravitation being "instantaneous" was part of the old Newtonian action-at a distance theory, which has since been displaced by general relativity.

Re: velocities at different distances, one does not need to know anything other than the basic Hubble law: v= Hd

where v is the velocity of the object (say distant quasar), H is the Hubble constant, and d is its distance.

Thus, since the new H = 67.15 kilometers per second per million parsecs, it leads to a slightly different result - say for velocities- than the older value of 70 km/sec/ Mpc

Anyway, these are some sources which you can access at a good library,  to clarify many of the issues you bring up:

1- Chapter 5 of Lawrence Krausse 'A Universe from Nothing'. In this chapter ('The Runaway Universe') Krausse clearly explains the difficulty in ascertaining acceleration of the cosmos, and also argues that one group's results may have been prematurely adopted.

Indeed, the most recent results from the European Space Agency's Planck Satellite (actually Space Telescope), disclose the cosmos may not be accelerating - or at least to the same extent as believed and is somewhat older at 13.82b years.

2- 'Will Dark Energy Tear The Universe Apart?' in ASTRONOMY (Feb., 2009). This article explains clearly the role of dark energy in cosmic acceleration and ties it to a negative pressure. Specifically the term (rho + 3p) acts as a source of gravity in general relativity, (where rho = energy density, p is gas pressure).

Again, the above sources can help fill in the blanks.

Your question highlights a common dilemma in that intelligent and curious people - but without adequate physics backgrounds- can become engrossed with science TV programs but which often elicit more questions than they can answer. The problem is that the combination of lack of physics background and lack of details in the programs themselves engenders misconceptions.

Hopefully, you will find this answer useful and also be able to obtain the sources shown.

Astrophysics

Volunteer

#### Philip A. Stahl

##### Expertise

I specialize in stellar and solar astrophysics. Can answer questions pertaining to these areas, including: stellar structure and evolution, HR diagrams, binary systems, collapsars (black holes, neutron stars) stellar atmospheres and the spectroscopic analysis of stars – as well as the magnetohydrodynamics of sunspots and solar flares. Sorry – No homework problems done or research projects! I will provide hints on solutions. No nonsense questions accepted, i.e. pertaining to astrology, or 'UFOs' or overly speculative questions: 'traveling through or near black holes, worm holes, time travel etc. Absolutely NO questions based on the twaddle at this Canadian site: http://members.shaw.ca/warmbeach/FAQ.htm purporting to show a "new physics". Do not waste my time or yours by wasting bandwidith with reference to such bunkum.

##### Experience

Have constructed computerized stellar models; MHD research. Gave workshops in astrophysics (stellar spectroscopy, analysis) at Harry Bayley Observatory, Barbados. More than twenty years spent in solar physics research, including discovery of SID flares. Developed first ever consistent magnetic arcade model for solar flares incorporating energy dissipation and accumulation. Developed first ever loop-based solar flare model using double layers and incorporating cavity resonators. (Paper presented at Joint AGU/AAS Meeting in Baltimore, MD, May 1994)

Organizations
American Astronomical Society (Solar physics and Dynamical astronomy divisions), American Geophysical Union, American Mathematical Society, Intertel.

Publications
Papers appearing in Solar Physics, Journal of the Royal Astronomical Society of Canada, Journal of the Barbados Astronomical Society, Meudon Solar Flare Proceedings (Meudon, France). Books: 'Fundamentals of Solar Physics', 'Selected Analyses in Solar Flare Plasma Dynamics', 'Physics Notes for Advanced Level', 'Astronomy & Astrophysics: Notes, Problems and Solutions', 'Modern Physics: Notes, Problems and Solutions'

Education/Credentials
B.A. degree in Astronomy; M.Phil. degree in Physics - specializing in solar physics.

Awards and Honors
Postgraduate research award- Barbados government; Studentship Award in Solar Physics - American Astronomical Society. Barbados Astronomical Society award for service (1977-91) as Journal editor.

Past/Present Clients
Caribbean Examinations Council (as advisor, examiner), Barbados Astronomical Society (as Journal Editor 1977-91), Trinidad & Tobago Astronomical Society (as consultant on courses, methods of instruction, and guest speaker).